Software Technology for “Implantable medical device that can be used with a single coil for multi-function”

Medical Device – Jordi Parramon, Matthew I. Haller, Boston Scientific Neuromodulation Corp

Abstract for “Implantable medical device that can be used with a single coil for multi-function”

A combination charging/telemetry circuit that can be used within an implantable device such as a microstimulator uses one coil to provide both charging and data telemetry. One aspect of the invention states that one or more capacitors can be used to tune the single coil’s frequency to various frequencies. The coil can then be used for both receiving power from external sources and for telemetry information.

Background for “Implantable medical device that can be used with a single coil for multi-function”

The present invention is related to implantable medical devices and, more specifically, to a voltage converter that can be used within an implantable microstimulator or similar implantable device. It uses an RF powering coil instead capacitors to provide voltage step-up/step-down functions. The invention also covers an implantable medical device that uses a single coil for both charging and telemetry, possibly at two different frequencies.

Many implantable medical devices such as sensors and neural stimulators use a battery to provide primary operating power. Others, like cochlear stimulators rely on an alternating magnetic force to induce an ac current into the implantable device. The induced voltage is then rectified and filtered to provide primary operating power to the device. There is a need to draw other operating voltages from the primary power source for both RF-powered and battery-powered devices. This means that there is often a need to increase the voltage from the primary power source to higher levels in order to generate high stimulation currents or other purposes. In some cases, it is also necessary to reduce the voltage of the primary source to a lower level for certain types of circuits, to conserve power.

A charge-pump voltage conversion circuit is used to perform the voltage step up or down function. In order to step up or down a primary voltage source, charge pump circuits usually rely on a network capacitors and switches. A network of four capacitors may be connected parallel through a switching network to increase the primary voltage source. Each capacitor will then charge to the voltage of its primary power source. If a battery is used to power the primary power source, then the voltage of that source is the voltage of the capacitors. After being charged, the capacitors can be switched to create a voltage across their series connections that is four times that of the primary voltage source. This higher voltage charge can then be transferred to another capacitor (e.g., to a holding cap), and the process of charging parallel-connected capacitors and switching them in series and then transferring charge to a holding cap is repeated until the capacitor’s charge is four times greater than the primary power source.

While charge-pump circuits are effective in performing step up/step down functions, they require large numbers of capacitors. These capacitors can be very large and bulky. Large numbers of capacitors in charge pump circuits can be too bulky for small implantable medical devices. Inefficient and slow in operation, charge pump circuits are also a problem. A voltage converter circuit is required that can perform the step-up or down function efficiently and quickly without the need for large quantities of bulky capacitors.

The present invention addresses these and other needs by providing a voltage conversion for small implantable electric devices such as microstimulators. This converter uses a coil instead of capacitors to provide voltage step up/step down functions. This converter can be controlled or adjusted by duty-cycle and/or ON/OFF moderation. This allows for high efficiency at virtually any voltage in the compliance range.

One aspect of the invention is applicable to implantable devices that have an existing RF-coil through which primary or charging energy is received. The existing RF-coil is used in a time multiplexing scheme to receive the RF signal as well as the voltage conversion function. This reduces the number and complexity of the components within the device. It also allows for the device to be packaged in smaller housings or provides additional space for other circuit components. This results in an implantable device with a voltage converter that is smaller and/or denser than other implantable devices.

According to another aspect of the invention, the voltage-up/down converter circuit can be controlled by pulse width modulation and/or ON/OFF modulation (OOM). Low power control circuits are also possible. This operation allows for high efficiency across a wide range output voltages and current loads.

According to another aspect, the invention provides an implantable device that contains a coil. The coil can be used for multiple purposes such as receiving power from external sources and part of a voltage converter circuit. Alternately, or together, the coil can be used to receive command information from an outside source as well as part of a voltage converter circuit.

“The present invention provides a voltage converter circuit that can be used within an implantable device. It is, for example, an implantable microstimulator (or similar type of neural stimulator) that is compact and efficient and offers a wide range output voltages and currents.

“It is another feature of the invention that a voltage converter circuit can be provided that does not require the use of a network capacitors switched between parallel or series configurations to provide step up and fall voltage conversion functions.

“Accordingly to another aspect, the invention provides an implantable device that contains a single coil and one or more capacitors. These capacitors are used to tune the coil at different frequencies. The different frequencies can be used for receiving power from external sources and for telemetry information to and from external sources.

The following description is the best way to carry out the invention. This description should not be taken as a limitation, but it is intended to describe the general principles of invention. It is important to refer to the claims when determining the scope of the invention.

The present invention is a type of voltage converter that can be used in an implantable medical device. It may include an implantable sensor, pump, or other medical device performing a desired medical function. Although the invention is described herein in relation to an implantable stimulator it should be understood that the invention can be used with many other types of implantable devices.

“A typical implantable stimulation device is helpful in understanding the context in which the invention will be used. Referring to FIG. 1, a block diagram of a representative implantable stimulation system 10 is illustrated. FIG. 1 illustrates a block diagram for an implantable stimulator system 10. The system 10 includes an implant device 20 that is placed under the skin 18 and connected to an external control 12 via an implanted coil 22 or external coil 15. The external coil 15 is usually carried in a housing 14. It is connected via flexible cable to the external control 12 unit 12. The external control unit is powered by an external power source 16. This could be a rechargeable or replacement battery. Through the link between the coils 15-22, the external power source 16 can also provide operating power to the implant device 20. This may be either continuous or intermittent. Intermittent power can be provided, for example, when an implant device has a rechargeable power source and the battery is periodically recharged.

The implant device 20, which acts as a stimulator, contains a plurality electrodes 24a and 24b that are connected to the implant 20 via conductive wires 23a and 23b. The electrodes 24a and 24b are usually placed near the body or nerves 26 to stimulate.

“In operation, system 10 works as follows: Implant device 20 and electrodes 24a and 24b are placed in the desired place under patient’s skin. In FIG. 1, the implant coil 22 can be seen separately from the device 20. The coil 22 is usually mounted to or housed in the same hermetically sealed case that houses the electronic circuitry of the implant device 20. The external control unit 12 transfers power and/or control data to the implant device via electromagnetic coupling between external coil 15 and implant coil 22. Once the control signals have been received or steered by program data, the implant device 20 will operate as directed to produce electrical stimulation pulses to deliver to the tissue 26 via electrodes 24a and 24b.

“Some implant devices 20 don’t have an embedded power source. These devices must receive their operating power from an external control unit. Others implant devices 20 contain an implanted source of power, such as a rechargeable battery. These devices receive their operating power from this source. These devices should be charged with the implanted power source on a regular basis or periodically. This is done via a link to the external control unit 12 or an equivalent device through the coils 22, and 15.

“FIG. “FIG. The microstimulator device 30, which includes electrical circuitry 32, is enclosed in a hermetically sealed case 34. The case 34 has electrodes 36a and 36b at each end. These 36 a-36 b electrodes are electrically connected with the 32 electrical circuitry via conductors, such as wires 37 a-37 b and wires 37 a-37 b. The appropriate feed-through conductors 38a-38 b pass through the wall of hermetically sealed case 34.

The advantage of microstimulator 30 is its small size and ease of use. It can be easily inserted at the desired location using the lumen of a hypodermic or other cannula. U.S. Pat. 103,237 discloses one embodiment of a microstimulator. No. No. 5,324,316 is incorporated herein as a reference. U.S. Pat. 103,316 discloses one method for making such a microstimulator. No. No.

FIG. 3 is a reference to the invention’s advantages. 3. Here is a functional block diagram showing a typical implantable stimulator 40. FIG. FIG. 3 shows the electronic circuitry of the stimulator 40. It includes an energy receiver 42 and a data receiver 44. A power source 46 is also included. A control circuit 48, voltage converter 50, pulse generator 52, and back telemetry circuit 54 are all functions of the stimulator. The stimulator 40 may receive power and data signals through an implanted coil 56. This coil is connected to the data receiver 44 as well as the energy receiver 42. A second coil 58, which may contain the same or part of the coil 56 in certain embodiments, is connected to both the energy receiver 42 and the data receiver 44. It provides a means by which back telemetry data can be sent to an outside receiver. This external receiver could be found in the external control unit 12 (FIG. 1). The stimulator 40’s components are contained in a sealed housing, or case 60. This allows the stimulator to be implanted into body tissue.

A plurality of electrodes (62 a,62 b) are located externally to the housing 60. They can still be implanted in body tissue. An electrical connection is made with the plurality electrodes 62a,62b through a plurality wire conductors (63a,63b) that are connected to a plurality feed-through connectors 64a,64b through the hermetically sealed wall of the case 60. The pulse generator 52 is electrically connected to the plurality 64 a- 64 b feed-through connectors on the interior of the case 60.

“In operation, an radio frequency signal (represented in FIG. 3, represented by the wavy-arrow 66), is received via coil 56. The RF signal is typically a modulated carrier signals. The energy receiver 42 rectifies the carrier signal and supplies power to the power source 46. The data receiver 44 demodulates the carrier signal and retrieves control and/or programming data for the control circuit 48. The control circuit 48 is typically a microprocessor and includes memory circuitry (not illustrated) that may store programming or control data. The control circuit 48 is based on the programming and/or control data and drives the pulse generator circuit 52 to generate and deliver electrical stimulation pulses for the patient through selected groups of the plurality electrodes 62a, 62b.

The compliance voltage is the difference between the supply voltage Vc and the output voltage Vo. The ideal pulse generator circuit 52 has a compliance voltage of 0.2V. This is because the power dissipated by the pulse generator circuit (which is not power delivered to the tissue) equals the square of its compliance voltage. The compliance voltage can’t always be reduced because the current delivered to the tissue by the electrodes 62a and 62b is variable over time. Therefore, the compliance must also fluctuate over time.

In some implantable stimulators 40 the voltage converter circuit 50 adjusts the supply voltage Vc to preserve power. It is typically used to supply a limited number of discrete levels as a function the current that will be delivered to the tissue. A typical voltage converter circuit 50 could provide one of four supply voltages VC for the pulse generator circuit 52. This is a function the amplitude of stimulation pulse to be delivered to tissue. U.S. Patent No. 626933 describes an implantable stimulator with such a feature. No. No.

It is evident that the voltage converter circuit 50 plays an important role in the implantable stimulator forty. The voltage converter circuit 50 is an additional circuitry, which requires large circuit components. This takes up valuable space in the case 60 and also consumes more power. Inefficient voltage converter circuits 50 are another problem. A capacitor charge pump circuit may, for instance, operate at efficiencies below 50%. For most stimulators (e.g., the one shown in FIG. 2 Space and power considerations are crucial to the design of the stimulator.

The present invention provides circuitry that can be used in an implantable stimulator device. It does the voltage conversion function with fewer and smaller components. This allows for more space in the case, which can be used to perform other functions or makes the case smaller. It also consumes less power. The present invention also allows for fewer circuit components in the stimulator design. This makes it smaller and more compact.

“Turning next, FIG. 4. A fly back converter circuit can be used to increase the voltage from a power source without using a switched capacitor network. FIG. 4 shows the flyback circuit. 4. The inductor or coil, L1, is connected at one end to the power source 70. The coil’s other end is connected to the first circuit node 72. Between the first node 72, ground, is connected a switching transistor M1. The transistor M1 is equipped with a gate terminal (73) and a duty cycle control circuit (74). The transistor M1 can be turned ON by applying a signal at its gate terminal 73. Node 72 will then be switched to ground potential via a low impedance path. Transistor M1 is turned off by not applying a signal to its gate terminal. This creates a very high impedance pathway and keeps node 72 isolated from ground.

“Also connected with node 72 in the fly back circuit illustrated in FIG. 4. is the cathode end of diode 1. An output node 75 is connected to the anode side. Between the output node 75, ground, and an output capacitor C1, a connection is made for an output capacitor. FIG. 4. A phantom resistor RL is connected between ground and the output node75.”

“Still with regard to FIG. “Still with reference to FIG. A high voltage applied at the gate of M1 could turn M1 ON (provide low impedance between node 72, ground) and a lower voltage may turn M1 off (provide high impedance between node 72, ground). The duty cycle control circuit (74) can generate a pulsed signal that 81, which applies a sequence of high- and low voltages to transistor M1. The transistor M1 turns ON when a pulse is present. If a pulse is absent, the voltage drops and the transistor M1 turns OFF.

The?duty cycle’ is the ratio of the time the pulse is high to total cycle time. FIG. 5. FIG. FIG. 5 shows that a pulsed signal (81) consists of a series of pulses 80. Each pulse 80 consists of a high voltage over a time period T2 and a lower voltage over a time period T3. T2 + T3 is the total cycle time. The duty cycle is usually expressed as a percentage. It is calculated as T2/T1 (or T2/(T2+T3)). Therefore, the duty cycle can vary from 0% when you have T1=0 to 100% when you have T1=T2.

“The operation and maintenance of FIG. 4. is well-known in the art. The basic idea is that when transistor M1 turns ON, circuit node 72 is connected with ground. This connects one end of the coil L1 and ground. The connection of one end of the coil L1 with ground causes an electric current to begin flowing from the power source 70 through inductor coil C1. After T2 is over, however, node 72 becomes float (is not connected with ground) and the voltage at node72 rises to a high level (higher than the power source voltage VS). As electrical current flows through coil L1, through diode A1, to charge capacitor, C1. During time T2, current begins to flow through coil L1, which causes the coil to store electromagnetic energy. This energy is then transferred to capacitor C1 during time T3. Thus, C1 is charged. C1 eventually charges to a voltage higher than the power source voltage Vs. This happens over many cycles. Thus, the stored charge on capacitor C1 provides an output voltage VOUT that is greater than VS and causes an output current IO through load resistor RL.

Adjusting the duty cycle of the signal 81 can be used to control the output voltage VOUT or IO. VOUT and IO will increase with a higher duty cycle, while VOUT and IO will decrease with a lower duty. The duty cycle control circuit (74) can also be called a pulse width modulator circuit, as it adjusts the pulse width (T2) from the pulses 80.

“Still with regard to FIG. 4. It should be noted that feedback can optionally be used to control and regulate VOUT’s output voltage. A sensing circuit (76A) may be used to measure the output voltage VOUT and compare it to a reference voltage VREF or a programed reference signal PROG. This is typically presented to the sensing device 76A as digital signals. On signal line 76C, the sensing circuit generates a difference sign. This signal represents the difference between the sensed out voltage VOUT and the reference or PROG voltages. This difference signal controls the gate control circuit (76B), which modulates transistor M1’s gate to drive the difference signal zero.”

“Turning next, FIGS. 6A-6E are additional simplified schematic diagrams of circuits that can be used in accordance to the present invention to achieve desired function. The circuit in FIG. 6A may be used to achieve a voltage step-up function. 6A: The circuit in FIG. may be used to achieve a voltage-step down function. 6B: The circuit of FIG. may be used to achieve an energy reception function. 6C; the circuit of FIG. may be used to achieve a data reception function. 6D; the circuit of FIG. may be used to achieve a data transmission function. 6E. Many of the components in FIGS. 6E are advantageously. 6A-6E could be identical. Common reference numbers are used to denote components that may be identical. Next, we will give a brief description of each function.

“FIG. 6A shows a circuit performing a voltage step-up function. The circuit in FIG. 6A is essentially the same as that described previously. The load resistance RL is not illustrated in this circuit. It is possible that a load resistance might be present. FIG. FIG. 4 shows the duty cycle control circuit controlling switch M1, FIG. 6A is a PWM (pulse-width modulation) control circuit. Controlling switch M1. These circuits serve the same purpose (turning switch 1 ON or OFF), and are, for the purposes of the present invention, substantially the same.

“FIG. 6B shows a circuit that performs an voltage step down function. FIG. FIG. 6B shows that a coil L1 connects between circuit nodes 75 & 76. Node 75 is the output node, where the output voltage VOUT can be found. Between node 75, ground, is connected capacitor C1. The node 76 is the anode end of a diode, while ground is the cathode. The anode side of a transistor switch is connected at node 75, and the other leg is connected to power source 70 at node 7. The pulse-width modulation control circuit 74 is connected to the gate terminal 78.

“FIG. 6C is a circuit that receives electricity from an external source. FIG. 6C shows the energy receive circuit. 6C shows a coil with a capacitor C2 attached in parallel to the coil L1. One side of this parallel connection is grounded. An?LC? is formed by the capacitor C2 and coil L1. Circuit that is tuned to an incoming radio frequency 83 (represented in FIG. 6C is represented by a wavy-arrow. Diode C1 is connected between output node 775 and the other side L1-C2 parallel connections, while the cathode for D1 is connected to node 7. Capacitor C1 connects between output node 75, ground.”

The circuit in FIG. 6C receives the incoming radio signal 83 via coil L1, and is tuned to the frequency 83 by capacitor. The signal is rectified by diode D1, which stores the positive half cycles on capacitor C1. The voltage that is generated on capacitor C1 acts as an output voltage VOUT to be used within the implant device.

“Next, in FIG. A data receiver circuit is shown in FIG. 6D. This data receiver circuit features coil L1 connected in parallel to variable capacitor C3. Modulated RF signal 88 The coil L1 receives the modulated RF signal 88? The value of C3 can be adjusted as needed so that the L1?C3 circuit tunes to the frequency of the modulation applied to incoming RF signals 88?. Node 72 is an output node in the L1-C3 circuit and is connected to an amplifier U1. The amplifier U1 provides an output signal. It includes a Data Out signal, which reflects the modulation applied on the incoming modulated radio signal 88?.

“Turning towards FIG. 6E is a simplified data transmitter circuit. A coil L1 is connected in parallel to an adjustable variable capacitor (C3). The power source 70 is connected to one side of the L1?C3 parallel connection. The other side, known as node 72, is connected to a power source 70. FIG. FIG. 6E is connected to anode D3. The switch transistor M3 connects the cathode to ground. A?Data Mod? drives the gate terminal of switch 3 (data modulation) signal. In operation, switch M3 closes and a current is drawn from the parallel circuit L1-C3. If switch M3 is opened, no current is drawn through L1-C3 parallel connections. As controlled by the Data Mod signal’s on-off pattern, the on-off current flows through the L1?C3 parallel connection. This causes a varying current through coil L1. As is well known, this current flows through the L1-C3 parallel connection, causing a varying magnetic force, which causes an RF signal (89) to be transmitted from coil L1.

“It is evident that the circuits shown in FIGS. 6A-6E perform the functions of voltage step down (FIG. 6A), Voltage step down (FIG. 6A), voltage step down (FIG. 6B), energy reception (FIG. 6C), data reception (FIG. 6E). These functions are usually required in an implantable stimulator device. 3).”

“In order perform the functions provided in FIGS. The present invention advantageously blends all functions of each circuit in FIGS. 6A-6E. This allows for a reduction in the number of circuit components required to perform the functions. 6A-6E are combined into one circuit, as shown in FIG. 7. This combination circuit is sometimes referred to by the term “voltage converter using an R-powering coil”, and it is especially suitable for implantable medical devices such as an implantable neural stimulationator.

“The combined circuit of the present invention (shown in FIG. 7. The circuit, which is shown in FIG. 7, uses an RF-powering coil and other elements to receive RF power from external sources. To transmit control data to the circuit, modulation may be done to the received RF power. This RF-powering coil can also be used to transmit data from the circuit. The RF-coil that is used to receive power, transmit power and data may also be used to convert received power (i.e. voltage) up or down to optimize the operation of the circuit.

“The circuit shown in FIG. 7 (i.e., the voltage converter circuit using an RF-powering coil provided by the present invention) includes a receiving/transmitting coil L1?. The coil L1? The coil L1? includes the ends that are attached to circuit nodes 72 and 85? respective 85 and 72? Node 85 is then connected via transistor switch M1. Source voltage VS. The coil L1? The coil L1? also includes a tap-point 85?, where N2 turns of this coil are between tap point 85 and tap point 85? Node 85 and N1 turns between tap points 85 and 85. Node 72? The coil L1? The total number of turns for coil L1? is N, where N=N1+N2. Representative values for N1 range from 10 to 100 turns to N2 between 10 and 100 turns. For N2, there are also 10 to 100 turning. Whereas the inductance of coil 1? is between 10 and 100 microhenries. In some embodiments however, N1 or N2 can vary between 1 and 1000 turns and L1? can vary from 1 to 1000 pH.”

“Still with regard to FIG. 7 is a series of capacitors C3 and M4. Circuit node 72 is connected to the transistor switch M4. Tap point 85?. A second transistor switch M5 connects to tap point 85 What is coil L1? to ground (node 85). Another transistor switch M2 connects tap point 85. “To the source voltage VS.”

“The tap point 85 is connected to the cathode end D2 of a diode. What is the coil L1? ; the ground is connected to the anode end diode D2

“The anode end of another diode, D3, is connected to node 72?” The anode of diode 3 is connected to ground via transistor switch M3. (node 85). The signal amplifier U1’s input is also connected to the anode end diode 3″.

“The anode end of another diode D1 is also connected with node 72?” Circuit node 75 is connected to the anode end diode D1. Between node 75? and capacitor C1, Ground (node 85) and a capacitor C1. Circuit node 75? This is where the output voltage VOUT is available when the circuit is in a voltage step-up or step-down mode. A suitable voltage clamp circuit (91) may be connected between node 75 and the output node 75. To prevent voltage at output node 75 from exceeding a predetermined value, a suitable voltage clamp circuit 91 may be connected between node 75 and ground. “From exceeding a predetermined value.”

“It can be seen that FIG. 7 contains five transistor switches M1?,M2 and M3, M3,M4 and M5. These five transistor switches determine which circuit function is performed, depending on whether they are ON, OFF or modulated using signal data or PWM data. 8. As shown in FIG. 8 To enable the circuit in FIG. 8 to enable the circuit of FIG. switch M1 is turned ON, and M2 is turned off. M3 is modulated using a PWM signal generated by a suitable duty cycle controller circuit (see FIGS. 4, 5, and M4 and M5 can be turned OFF. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6A is reduced by adding diode D3 in series to switch M3 (which does not affect the operation of the circuit). As explained above, this configuration and mode determines the output voltage VOUT in large part based on the duty cycle of the signal applied at the gate of transistor switchM3.

“Similarly, as described in FIG. 8 for the circuit in FIG. Switch M1 is used to switch the voltage step down mode. Switch M1 is turned off, and switch M2 is modulated by a PWM signal from an appropriate duty cycle control circuit. (FIG. 6B), and the switches M3,M4 and M5 are all OFF. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6B with diode D1 connecting between nodes 72 and 75. 75? (which diode doesn’t significantly alter circuit operation) and only a small portion of coil L1? Only the N1 turns are used. The circuit performs a voltage-step down function in such configuration and mode as previously described in connection to FIG. 6B.”

“As defined by FIG. 8 The circuit in FIG. 7 can also be selectedly operated in both an energy receive and data receive mode by turning switches OFF M1?, M2 or M3 and turning ON M4 and M5. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6C and FIG. 6D with only a small portion (N1 turn) of the coil. as part of the circuit. The circuit of FIG. The circuit of FIG. 7 performs the energy receive function described in connection to FIG. 6C and a data receiving function as described in FIG. 6D.”

“As further described in FIG. 8 The circuit in FIG. 7. The circuit of FIG. ON. Depending on whether capacitor C3 is present, switch M4 can be switched OFF or ON. If coil L1 is not being tuned properly, it may be necessary to adjust the switch M4. Data transmission is efficient. Capacitor C3 is required for many data transmissions. It is not necessary. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6E. 6E. 6E.”

“It is evident that the circuit in FIG. 1 can be controlled by selectively controlling the states of the switches M1′, M2?, and M3?. 7, may be used in any of the five modes. These modes may be used simultaneously, such as the energy receive mode or the data receive mode. Other modes can be invoked in time-multiplexed fashion, such as a first mode followed by a second and then a third, depending on the application. For example, an energy-and-data receive mode could be used to enable the device to receive operating powers (e.g., to recharge a battery), and/or initial programming control signals. The first mode can then be followed by a second one, e.g., the voltage step up mode. This mode is initiated by changing M1?,M2 and M3 states as shown in FIG. 8 during which the voltage from the primary power source is increased to the voltage that the device requires to function properly. A third mode, such as a data transmitting mode, can be used if necessary to enable the implant device’s data transmission to an external receiver.

“The component values, i.e. the transistor switches, capacitors, and coil used in the circuit shown in FIG. 7. may be easily determined by those skilled in the art for a specific application and desired frequency.

FIG. 9. The single-coil circuitry in FIG. 9 can transmit and receive data and receive power to charge the implantable medical device. Similar to earlier circuitry, the tunable nature is also present. It can be tuned to one frequency to transmit data and another to receive power. FIG. 9 shows the circuitry. FIG. 9 may also be used to perform the step-up and step-down features discussed previously, but those aspects are not shown.”

“The circuit of FIG. The circuit of FIG. 9 includes coil M2. The coil L2 is connected to one end by transistor switch M6 to supply power source voltage Vs and the other end via transistor switch M7, to ground. Parallel to coil L2, C4 is also connected. Parallel to coil L2 is also connected a series combination of a transistor switch M8 and a capacitor C5. Parallel to coil L2 is also connected the full bridge rectifier, represented by diodes 5, D6 and D7 that produces DC voltage VOUT. A full bridge rectifier is expected to have a transfer efficiency of about 15% more than a single diode or half-wave rectifier. These other options could be used to produce VOUT. The ground and rectifier circuitry are also connected by a transistor switch M9.

“DC voltage VOUT” is received at storage capacitor CC6, which smoothes out the voltage before it is passed to charging circuitry 92. The charging circuitry 92 is used for controlling the charge of battery source 93. To prevent VOUT exceeding a predetermined value, a Zener diode or another suitable voltage clamp circuit can be connected to capacitor C6.

“FIG. 10. shows the status of the transistor switches M6, M7, and M8 for energy receive, data transmit, and data receive modes. FIG. FIG. 10. The circuit in FIG. 9 will operate in energy receive mode. The circuit will turn switches M6 and M7 OFF and switch M8 ON. To turn M8 ON, capacitor C5 is connected with capacitor C4, which together with the inductance created by coil L2, form a resonant loop that tunes to the frequency of the RF signal (83) sent from the external control unit 12. For example, f1 could be around 80 kHz.

“The circuit shown in FIG. 9 can also be used in data transmit mode while charging, by using back telemetry known Load Shift Keying. U.S. Application Ser. No. No. 12/354,406, filed January 15, 2009 during LSK. The impedance of FIG. 9 can be modulated by controlling transistor switch M9 with the transistor’s off-resistance providing necessary modulation. The change in impedance of the coil is reflected back into the external control 12 unit 12, which generates the RF signal 83. This reflection is then demodulated at 12 unit external to recover the transmitted data. This method of transmitting data can be used to communicate information relevant during charging of battery 93 in microstimulator. It includes the capacity of the battery and whether the external charger should be stopped.

“For FIG. 9 will operate in data receive mode. The circuit will turn switches M6 and M8 OFF and switch M7 ON. The resonant circuit’s tuning is governed by capacitor C4 and coil L2. The resonant circuit tunes to a higher frequency, f2 with capacitor C5 removed. This corresponds to the modulated radio signal 88? The external control unit 12 receives the RF data signal. (The external control device 12 that sends RF data signal number 88 to the microstimulator. The external control unit 12 that sends RF data signal 88 to the microstimulator can be either the same device or separate. Although the external control units 12 may include multiple devices, FIG. 12 shows the external control module 12 as a single device. 9 for ease of reference). For example, f2 could be approximately 125kHz. This can be a center frequency for the modulated data in RF signal 88′. If the RF signal number 88?, for example, A logic?0 might be generated when the RF signal 88? is modulated according to a Frequency Shift Keying protocol. A logic?1 might contain a frequency that is slightly lower than the center frequency (e.g. 121 kHz). A logic?1 might contain a frequency slightly lower than the center frequency (e.g. 121 kHz), while a logic?1 could contain a frequency slightly above the center frequency (e.g. 129 kHz). Despite the slight differences, this band or range of frequencies can still be considered a single frequency. Turning M7 ON grounded the resonant circuit. This provides an input to receiver that demodulates the received data. A differential input, as shown in FIG. 9, can be used to build the receiver. 9 or a single-ended, non-differential input.

“As further illustrated in FIG. The circuit in FIG. 10 is also shown. 9, the circuit of FIG. The resonant circuit will be tuned to the higher frequency of f2 by turning transistor M8 off. It will also broadcast an RF signal to the external control units 12 according to these conditions. The power source voltage Vs is supplied via transistor M6. A transmitter will modulate the data at transistor M7 in accordance to the tuning of its resonant circuit. The center of the data will be around 125 KHz. The data signal that is presented to transistor M7 when transmitting logic?0 might include a 121kHz signal or a signal of 129kHz when transmitting logic?1. A transmitter could also be coupled to transistor M6.”

“It is evident that the circuit of FIG. can be controlled by selectively controlling the states of the switches M6,M7,M8 and M9. 9 can operate in different modes. These modes can be invoked in a time-multiplexed fashion, e.g. a first mode may be followed by a second, depending on the application. Tuning allows for charging at a frequency f1 and data transmission at a frequency f2. The circuitry in FIG. 9 has been optimized for charging at lower frequencies (e.g. 80 kHz) than higher frequencies due to heat concerns. Higher frequencies, such as 125 kHz have been shown to allow for higher bandwidth and higher data rates. Like other tunable circuits described herein, FIG. 9 provides an optimized design for charging and telemetry that uses only one coil. Variable capacitors could be substituted for capacitors C4 or C5 in order to achieve similar tuning.

“It can be seen that the invention described in this document provides a voltage conversion circuit for use in an implantable device. It is, for example, an implantable microstimulator (or similar type of neural stimulationator), that is compact and efficient and offers a wide range output voltages or currents.

“It can also be seen that the invention provides a voltage convert circuit that eliminates the need for a network capacitors switched between parallel or series configurations, or any other configurations, in order to provide step up and drop voltage conversion functions.”

“It can also be seen that the invention contains an implantable device that has a single coil that can be tunable at different frequencies for charging or telemetry.”

“While the invention disclosed herein has been described using specific embodiments and their applications, many modifications and variations could still be made by those skilled in art without departing form the scope of the invention as set forth in its claims.”

Summary for “Implantable medical device that can be used with a single coil for multi-function”

The present invention is related to implantable medical devices and, more specifically, to a voltage converter that can be used within an implantable microstimulator or similar implantable device. It uses an RF powering coil instead capacitors to provide voltage step-up/step-down functions. The invention also covers an implantable medical device that uses a single coil for both charging and telemetry, possibly at two different frequencies.

Many implantable medical devices such as sensors and neural stimulators use a battery to provide primary operating power. Others, like cochlear stimulators rely on an alternating magnetic force to induce an ac current into the implantable device. The induced voltage is then rectified and filtered to provide primary operating power to the device. There is a need to draw other operating voltages from the primary power source for both RF-powered and battery-powered devices. This means that there is often a need to increase the voltage from the primary power source to higher levels in order to generate high stimulation currents or other purposes. In some cases, it is also necessary to reduce the voltage of the primary source to a lower level for certain types of circuits, to conserve power.

A charge-pump voltage conversion circuit is used to perform the voltage step up or down function. In order to step up or down a primary voltage source, charge pump circuits usually rely on a network capacitors and switches. A network of four capacitors may be connected parallel through a switching network to increase the primary voltage source. Each capacitor will then charge to the voltage of its primary power source. If a battery is used to power the primary power source, then the voltage of that source is the voltage of the capacitors. After being charged, the capacitors can be switched to create a voltage across their series connections that is four times that of the primary voltage source. This higher voltage charge can then be transferred to another capacitor (e.g., to a holding cap), and the process of charging parallel-connected capacitors and switching them in series and then transferring charge to a holding cap is repeated until the capacitor’s charge is four times greater than the primary power source.

While charge-pump circuits are effective in performing step up/step down functions, they require large numbers of capacitors. These capacitors can be very large and bulky. Large numbers of capacitors in charge pump circuits can be too bulky for small implantable medical devices. Inefficient and slow in operation, charge pump circuits are also a problem. A voltage converter circuit is required that can perform the step-up or down function efficiently and quickly without the need for large quantities of bulky capacitors.

The present invention addresses these and other needs by providing a voltage conversion for small implantable electric devices such as microstimulators. This converter uses a coil instead of capacitors to provide voltage step up/step down functions. This converter can be controlled or adjusted by duty-cycle and/or ON/OFF moderation. This allows for high efficiency at virtually any voltage in the compliance range.

One aspect of the invention is applicable to implantable devices that have an existing RF-coil through which primary or charging energy is received. The existing RF-coil is used in a time multiplexing scheme to receive the RF signal as well as the voltage conversion function. This reduces the number and complexity of the components within the device. It also allows for the device to be packaged in smaller housings or provides additional space for other circuit components. This results in an implantable device with a voltage converter that is smaller and/or denser than other implantable devices.

According to another aspect of the invention, the voltage-up/down converter circuit can be controlled by pulse width modulation and/or ON/OFF modulation (OOM). Low power control circuits are also possible. This operation allows for high efficiency across a wide range output voltages and current loads.

According to another aspect, the invention provides an implantable device that contains a coil. The coil can be used for multiple purposes such as receiving power from external sources and part of a voltage converter circuit. Alternately, or together, the coil can be used to receive command information from an outside source as well as part of a voltage converter circuit.

“The present invention provides a voltage converter circuit that can be used within an implantable device. It is, for example, an implantable microstimulator (or similar type of neural stimulator) that is compact and efficient and offers a wide range output voltages and currents.

“It is another feature of the invention that a voltage converter circuit can be provided that does not require the use of a network capacitors switched between parallel or series configurations to provide step up and fall voltage conversion functions.

“Accordingly to another aspect, the invention provides an implantable device that contains a single coil and one or more capacitors. These capacitors are used to tune the coil at different frequencies. The different frequencies can be used for receiving power from external sources and for telemetry information to and from external sources.

The following description is the best way to carry out the invention. This description should not be taken as a limitation, but it is intended to describe the general principles of invention. It is important to refer to the claims when determining the scope of the invention.

The present invention is a type of voltage converter that can be used in an implantable medical device. It may include an implantable sensor, pump, or other medical device performing a desired medical function. Although the invention is described herein in relation to an implantable stimulator it should be understood that the invention can be used with many other types of implantable devices.

“A typical implantable stimulation device is helpful in understanding the context in which the invention will be used. Referring to FIG. 1, a block diagram of a representative implantable stimulation system 10 is illustrated. FIG. 1 illustrates a block diagram for an implantable stimulator system 10. The system 10 includes an implant device 20 that is placed under the skin 18 and connected to an external control 12 via an implanted coil 22 or external coil 15. The external coil 15 is usually carried in a housing 14. It is connected via flexible cable to the external control 12 unit 12. The external control unit is powered by an external power source 16. This could be a rechargeable or replacement battery. Through the link between the coils 15-22, the external power source 16 can also provide operating power to the implant device 20. This may be either continuous or intermittent. Intermittent power can be provided, for example, when an implant device has a rechargeable power source and the battery is periodically recharged.

The implant device 20, which acts as a stimulator, contains a plurality electrodes 24a and 24b that are connected to the implant 20 via conductive wires 23a and 23b. The electrodes 24a and 24b are usually placed near the body or nerves 26 to stimulate.

“In operation, system 10 works as follows: Implant device 20 and electrodes 24a and 24b are placed in the desired place under patient’s skin. In FIG. 1, the implant coil 22 can be seen separately from the device 20. The coil 22 is usually mounted to or housed in the same hermetically sealed case that houses the electronic circuitry of the implant device 20. The external control unit 12 transfers power and/or control data to the implant device via electromagnetic coupling between external coil 15 and implant coil 22. Once the control signals have been received or steered by program data, the implant device 20 will operate as directed to produce electrical stimulation pulses to deliver to the tissue 26 via electrodes 24a and 24b.

“Some implant devices 20 don’t have an embedded power source. These devices must receive their operating power from an external control unit. Others implant devices 20 contain an implanted source of power, such as a rechargeable battery. These devices receive their operating power from this source. These devices should be charged with the implanted power source on a regular basis or periodically. This is done via a link to the external control unit 12 or an equivalent device through the coils 22, and 15.

“FIG. “FIG. The microstimulator device 30, which includes electrical circuitry 32, is enclosed in a hermetically sealed case 34. The case 34 has electrodes 36a and 36b at each end. These 36 a-36 b electrodes are electrically connected with the 32 electrical circuitry via conductors, such as wires 37 a-37 b and wires 37 a-37 b. The appropriate feed-through conductors 38a-38 b pass through the wall of hermetically sealed case 34.

The advantage of microstimulator 30 is its small size and ease of use. It can be easily inserted at the desired location using the lumen of a hypodermic or other cannula. U.S. Pat. 103,237 discloses one embodiment of a microstimulator. No. No. 5,324,316 is incorporated herein as a reference. U.S. Pat. 103,316 discloses one method for making such a microstimulator. No. No.

FIG. 3 is a reference to the invention’s advantages. 3. Here is a functional block diagram showing a typical implantable stimulator 40. FIG. FIG. 3 shows the electronic circuitry of the stimulator 40. It includes an energy receiver 42 and a data receiver 44. A power source 46 is also included. A control circuit 48, voltage converter 50, pulse generator 52, and back telemetry circuit 54 are all functions of the stimulator. The stimulator 40 may receive power and data signals through an implanted coil 56. This coil is connected to the data receiver 44 as well as the energy receiver 42. A second coil 58, which may contain the same or part of the coil 56 in certain embodiments, is connected to both the energy receiver 42 and the data receiver 44. It provides a means by which back telemetry data can be sent to an outside receiver. This external receiver could be found in the external control unit 12 (FIG. 1). The stimulator 40’s components are contained in a sealed housing, or case 60. This allows the stimulator to be implanted into body tissue.

A plurality of electrodes (62 a,62 b) are located externally to the housing 60. They can still be implanted in body tissue. An electrical connection is made with the plurality electrodes 62a,62b through a plurality wire conductors (63a,63b) that are connected to a plurality feed-through connectors 64a,64b through the hermetically sealed wall of the case 60. The pulse generator 52 is electrically connected to the plurality 64 a- 64 b feed-through connectors on the interior of the case 60.

“In operation, an radio frequency signal (represented in FIG. 3, represented by the wavy-arrow 66), is received via coil 56. The RF signal is typically a modulated carrier signals. The energy receiver 42 rectifies the carrier signal and supplies power to the power source 46. The data receiver 44 demodulates the carrier signal and retrieves control and/or programming data for the control circuit 48. The control circuit 48 is typically a microprocessor and includes memory circuitry (not illustrated) that may store programming or control data. The control circuit 48 is based on the programming and/or control data and drives the pulse generator circuit 52 to generate and deliver electrical stimulation pulses for the patient through selected groups of the plurality electrodes 62a, 62b.

The compliance voltage is the difference between the supply voltage Vc and the output voltage Vo. The ideal pulse generator circuit 52 has a compliance voltage of 0.2V. This is because the power dissipated by the pulse generator circuit (which is not power delivered to the tissue) equals the square of its compliance voltage. The compliance voltage can’t always be reduced because the current delivered to the tissue by the electrodes 62a and 62b is variable over time. Therefore, the compliance must also fluctuate over time.

In some implantable stimulators 40 the voltage converter circuit 50 adjusts the supply voltage Vc to preserve power. It is typically used to supply a limited number of discrete levels as a function the current that will be delivered to the tissue. A typical voltage converter circuit 50 could provide one of four supply voltages VC for the pulse generator circuit 52. This is a function the amplitude of stimulation pulse to be delivered to tissue. U.S. Patent No. 626933 describes an implantable stimulator with such a feature. No. No.

It is evident that the voltage converter circuit 50 plays an important role in the implantable stimulator forty. The voltage converter circuit 50 is an additional circuitry, which requires large circuit components. This takes up valuable space in the case 60 and also consumes more power. Inefficient voltage converter circuits 50 are another problem. A capacitor charge pump circuit may, for instance, operate at efficiencies below 50%. For most stimulators (e.g., the one shown in FIG. 2 Space and power considerations are crucial to the design of the stimulator.

The present invention provides circuitry that can be used in an implantable stimulator device. It does the voltage conversion function with fewer and smaller components. This allows for more space in the case, which can be used to perform other functions or makes the case smaller. It also consumes less power. The present invention also allows for fewer circuit components in the stimulator design. This makes it smaller and more compact.

“Turning next, FIG. 4. A fly back converter circuit can be used to increase the voltage from a power source without using a switched capacitor network. FIG. 4 shows the flyback circuit. 4. The inductor or coil, L1, is connected at one end to the power source 70. The coil’s other end is connected to the first circuit node 72. Between the first node 72, ground, is connected a switching transistor M1. The transistor M1 is equipped with a gate terminal (73) and a duty cycle control circuit (74). The transistor M1 can be turned ON by applying a signal at its gate terminal 73. Node 72 will then be switched to ground potential via a low impedance path. Transistor M1 is turned off by not applying a signal to its gate terminal. This creates a very high impedance pathway and keeps node 72 isolated from ground.

“Also connected with node 72 in the fly back circuit illustrated in FIG. 4. is the cathode end of diode 1. An output node 75 is connected to the anode side. Between the output node 75, ground, and an output capacitor C1, a connection is made for an output capacitor. FIG. 4. A phantom resistor RL is connected between ground and the output node75.”

“Still with regard to FIG. “Still with reference to FIG. A high voltage applied at the gate of M1 could turn M1 ON (provide low impedance between node 72, ground) and a lower voltage may turn M1 off (provide high impedance between node 72, ground). The duty cycle control circuit (74) can generate a pulsed signal that 81, which applies a sequence of high- and low voltages to transistor M1. The transistor M1 turns ON when a pulse is present. If a pulse is absent, the voltage drops and the transistor M1 turns OFF.

The?duty cycle’ is the ratio of the time the pulse is high to total cycle time. FIG. 5. FIG. FIG. 5 shows that a pulsed signal (81) consists of a series of pulses 80. Each pulse 80 consists of a high voltage over a time period T2 and a lower voltage over a time period T3. T2 + T3 is the total cycle time. The duty cycle is usually expressed as a percentage. It is calculated as T2/T1 (or T2/(T2+T3)). Therefore, the duty cycle can vary from 0% when you have T1=0 to 100% when you have T1=T2.

“The operation and maintenance of FIG. 4. is well-known in the art. The basic idea is that when transistor M1 turns ON, circuit node 72 is connected with ground. This connects one end of the coil L1 and ground. The connection of one end of the coil L1 with ground causes an electric current to begin flowing from the power source 70 through inductor coil C1. After T2 is over, however, node 72 becomes float (is not connected with ground) and the voltage at node72 rises to a high level (higher than the power source voltage VS). As electrical current flows through coil L1, through diode A1, to charge capacitor, C1. During time T2, current begins to flow through coil L1, which causes the coil to store electromagnetic energy. This energy is then transferred to capacitor C1 during time T3. Thus, C1 is charged. C1 eventually charges to a voltage higher than the power source voltage Vs. This happens over many cycles. Thus, the stored charge on capacitor C1 provides an output voltage VOUT that is greater than VS and causes an output current IO through load resistor RL.

Adjusting the duty cycle of the signal 81 can be used to control the output voltage VOUT or IO. VOUT and IO will increase with a higher duty cycle, while VOUT and IO will decrease with a lower duty. The duty cycle control circuit (74) can also be called a pulse width modulator circuit, as it adjusts the pulse width (T2) from the pulses 80.

“Still with regard to FIG. 4. It should be noted that feedback can optionally be used to control and regulate VOUT’s output voltage. A sensing circuit (76A) may be used to measure the output voltage VOUT and compare it to a reference voltage VREF or a programed reference signal PROG. This is typically presented to the sensing device 76A as digital signals. On signal line 76C, the sensing circuit generates a difference sign. This signal represents the difference between the sensed out voltage VOUT and the reference or PROG voltages. This difference signal controls the gate control circuit (76B), which modulates transistor M1’s gate to drive the difference signal zero.”

“Turning next, FIGS. 6A-6E are additional simplified schematic diagrams of circuits that can be used in accordance to the present invention to achieve desired function. The circuit in FIG. 6A may be used to achieve a voltage step-up function. 6A: The circuit in FIG. may be used to achieve a voltage-step down function. 6B: The circuit of FIG. may be used to achieve an energy reception function. 6C; the circuit of FIG. may be used to achieve a data reception function. 6D; the circuit of FIG. may be used to achieve a data transmission function. 6E. Many of the components in FIGS. 6E are advantageously. 6A-6E could be identical. Common reference numbers are used to denote components that may be identical. Next, we will give a brief description of each function.

“FIG. 6A shows a circuit performing a voltage step-up function. The circuit in FIG. 6A is essentially the same as that described previously. The load resistance RL is not illustrated in this circuit. It is possible that a load resistance might be present. FIG. FIG. 4 shows the duty cycle control circuit controlling switch M1, FIG. 6A is a PWM (pulse-width modulation) control circuit. Controlling switch M1. These circuits serve the same purpose (turning switch 1 ON or OFF), and are, for the purposes of the present invention, substantially the same.

“FIG. 6B shows a circuit that performs an voltage step down function. FIG. FIG. 6B shows that a coil L1 connects between circuit nodes 75 & 76. Node 75 is the output node, where the output voltage VOUT can be found. Between node 75, ground, is connected capacitor C1. The node 76 is the anode end of a diode, while ground is the cathode. The anode side of a transistor switch is connected at node 75, and the other leg is connected to power source 70 at node 7. The pulse-width modulation control circuit 74 is connected to the gate terminal 78.

“FIG. 6C is a circuit that receives electricity from an external source. FIG. 6C shows the energy receive circuit. 6C shows a coil with a capacitor C2 attached in parallel to the coil L1. One side of this parallel connection is grounded. An?LC? is formed by the capacitor C2 and coil L1. Circuit that is tuned to an incoming radio frequency 83 (represented in FIG. 6C is represented by a wavy-arrow. Diode C1 is connected between output node 775 and the other side L1-C2 parallel connections, while the cathode for D1 is connected to node 7. Capacitor C1 connects between output node 75, ground.”

The circuit in FIG. 6C receives the incoming radio signal 83 via coil L1, and is tuned to the frequency 83 by capacitor. The signal is rectified by diode D1, which stores the positive half cycles on capacitor C1. The voltage that is generated on capacitor C1 acts as an output voltage VOUT to be used within the implant device.

“Next, in FIG. A data receiver circuit is shown in FIG. 6D. This data receiver circuit features coil L1 connected in parallel to variable capacitor C3. Modulated RF signal 88 The coil L1 receives the modulated RF signal 88? The value of C3 can be adjusted as needed so that the L1?C3 circuit tunes to the frequency of the modulation applied to incoming RF signals 88?. Node 72 is an output node in the L1-C3 circuit and is connected to an amplifier U1. The amplifier U1 provides an output signal. It includes a Data Out signal, which reflects the modulation applied on the incoming modulated radio signal 88?.

“Turning towards FIG. 6E is a simplified data transmitter circuit. A coil L1 is connected in parallel to an adjustable variable capacitor (C3). The power source 70 is connected to one side of the L1?C3 parallel connection. The other side, known as node 72, is connected to a power source 70. FIG. FIG. 6E is connected to anode D3. The switch transistor M3 connects the cathode to ground. A?Data Mod? drives the gate terminal of switch 3 (data modulation) signal. In operation, switch M3 closes and a current is drawn from the parallel circuit L1-C3. If switch M3 is opened, no current is drawn through L1-C3 parallel connections. As controlled by the Data Mod signal’s on-off pattern, the on-off current flows through the L1?C3 parallel connection. This causes a varying current through coil L1. As is well known, this current flows through the L1-C3 parallel connection, causing a varying magnetic force, which causes an RF signal (89) to be transmitted from coil L1.

“It is evident that the circuits shown in FIGS. 6A-6E perform the functions of voltage step down (FIG. 6A), Voltage step down (FIG. 6A), voltage step down (FIG. 6B), energy reception (FIG. 6C), data reception (FIG. 6E). These functions are usually required in an implantable stimulator device. 3).”

“In order perform the functions provided in FIGS. The present invention advantageously blends all functions of each circuit in FIGS. 6A-6E. This allows for a reduction in the number of circuit components required to perform the functions. 6A-6E are combined into one circuit, as shown in FIG. 7. This combination circuit is sometimes referred to by the term “voltage converter using an R-powering coil”, and it is especially suitable for implantable medical devices such as an implantable neural stimulationator.

“The combined circuit of the present invention (shown in FIG. 7. The circuit, which is shown in FIG. 7, uses an RF-powering coil and other elements to receive RF power from external sources. To transmit control data to the circuit, modulation may be done to the received RF power. This RF-powering coil can also be used to transmit data from the circuit. The RF-coil that is used to receive power, transmit power and data may also be used to convert received power (i.e. voltage) up or down to optimize the operation of the circuit.

“The circuit shown in FIG. 7 (i.e., the voltage converter circuit using an RF-powering coil provided by the present invention) includes a receiving/transmitting coil L1?. The coil L1? The coil L1? includes the ends that are attached to circuit nodes 72 and 85? respective 85 and 72? Node 85 is then connected via transistor switch M1. Source voltage VS. The coil L1? The coil L1? also includes a tap-point 85?, where N2 turns of this coil are between tap point 85 and tap point 85? Node 85 and N1 turns between tap points 85 and 85. Node 72? The coil L1? The total number of turns for coil L1? is N, where N=N1+N2. Representative values for N1 range from 10 to 100 turns to N2 between 10 and 100 turns. For N2, there are also 10 to 100 turning. Whereas the inductance of coil 1? is between 10 and 100 microhenries. In some embodiments however, N1 or N2 can vary between 1 and 1000 turns and L1? can vary from 1 to 1000 pH.”

“Still with regard to FIG. 7 is a series of capacitors C3 and M4. Circuit node 72 is connected to the transistor switch M4. Tap point 85?. A second transistor switch M5 connects to tap point 85 What is coil L1? to ground (node 85). Another transistor switch M2 connects tap point 85. “To the source voltage VS.”

“The tap point 85 is connected to the cathode end D2 of a diode. What is the coil L1? ; the ground is connected to the anode end diode D2

“The anode end of another diode, D3, is connected to node 72?” The anode of diode 3 is connected to ground via transistor switch M3. (node 85). The signal amplifier U1’s input is also connected to the anode end diode 3″.

“The anode end of another diode D1 is also connected with node 72?” Circuit node 75 is connected to the anode end diode D1. Between node 75? and capacitor C1, Ground (node 85) and a capacitor C1. Circuit node 75? This is where the output voltage VOUT is available when the circuit is in a voltage step-up or step-down mode. A suitable voltage clamp circuit (91) may be connected between node 75 and the output node 75. To prevent voltage at output node 75 from exceeding a predetermined value, a suitable voltage clamp circuit 91 may be connected between node 75 and ground. “From exceeding a predetermined value.”

“It can be seen that FIG. 7 contains five transistor switches M1?,M2 and M3, M3,M4 and M5. These five transistor switches determine which circuit function is performed, depending on whether they are ON, OFF or modulated using signal data or PWM data. 8. As shown in FIG. 8 To enable the circuit in FIG. 8 to enable the circuit of FIG. switch M1 is turned ON, and M2 is turned off. M3 is modulated using a PWM signal generated by a suitable duty cycle controller circuit (see FIGS. 4, 5, and M4 and M5 can be turned OFF. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6A is reduced by adding diode D3 in series to switch M3 (which does not affect the operation of the circuit). As explained above, this configuration and mode determines the output voltage VOUT in large part based on the duty cycle of the signal applied at the gate of transistor switchM3.

“Similarly, as described in FIG. 8 for the circuit in FIG. Switch M1 is used to switch the voltage step down mode. Switch M1 is turned off, and switch M2 is modulated by a PWM signal from an appropriate duty cycle control circuit. (FIG. 6B), and the switches M3,M4 and M5 are all OFF. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6B with diode D1 connecting between nodes 72 and 75. 75? (which diode doesn’t significantly alter circuit operation) and only a small portion of coil L1? Only the N1 turns are used. The circuit performs a voltage-step down function in such configuration and mode as previously described in connection to FIG. 6B.”

“As defined by FIG. 8 The circuit in FIG. 7 can also be selectedly operated in both an energy receive and data receive mode by turning switches OFF M1?, M2 or M3 and turning ON M4 and M5. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6C and FIG. 6D with only a small portion (N1 turn) of the coil. as part of the circuit. The circuit of FIG. The circuit of FIG. 7 performs the energy receive function described in connection to FIG. 6C and a data receiving function as described in FIG. 6D.”

“As further described in FIG. 8 The circuit in FIG. 7. The circuit of FIG. ON. Depending on whether capacitor C3 is present, switch M4 can be switched OFF or ON. If coil L1 is not being tuned properly, it may be necessary to adjust the switch M4. Data transmission is efficient. Capacitor C3 is required for many data transmissions. It is not necessary. The circuit shown in FIG. The circuit of FIG. 7 is effectively reduced to that shown in FIG. 6E. 6E. 6E.”

“It is evident that the circuit in FIG. 1 can be controlled by selectively controlling the states of the switches M1′, M2?, and M3?. 7, may be used in any of the five modes. These modes may be used simultaneously, such as the energy receive mode or the data receive mode. Other modes can be invoked in time-multiplexed fashion, such as a first mode followed by a second and then a third, depending on the application. For example, an energy-and-data receive mode could be used to enable the device to receive operating powers (e.g., to recharge a battery), and/or initial programming control signals. The first mode can then be followed by a second one, e.g., the voltage step up mode. This mode is initiated by changing M1?,M2 and M3 states as shown in FIG. 8 during which the voltage from the primary power source is increased to the voltage that the device requires to function properly. A third mode, such as a data transmitting mode, can be used if necessary to enable the implant device’s data transmission to an external receiver.

“The component values, i.e. the transistor switches, capacitors, and coil used in the circuit shown in FIG. 7. may be easily determined by those skilled in the art for a specific application and desired frequency.

FIG. 9. The single-coil circuitry in FIG. 9 can transmit and receive data and receive power to charge the implantable medical device. Similar to earlier circuitry, the tunable nature is also present. It can be tuned to one frequency to transmit data and another to receive power. FIG. 9 shows the circuitry. FIG. 9 may also be used to perform the step-up and step-down features discussed previously, but those aspects are not shown.”

“The circuit of FIG. The circuit of FIG. 9 includes coil M2. The coil L2 is connected to one end by transistor switch M6 to supply power source voltage Vs and the other end via transistor switch M7, to ground. Parallel to coil L2, C4 is also connected. Parallel to coil L2 is also connected a series combination of a transistor switch M8 and a capacitor C5. Parallel to coil L2 is also connected the full bridge rectifier, represented by diodes 5, D6 and D7 that produces DC voltage VOUT. A full bridge rectifier is expected to have a transfer efficiency of about 15% more than a single diode or half-wave rectifier. These other options could be used to produce VOUT. The ground and rectifier circuitry are also connected by a transistor switch M9.

“DC voltage VOUT” is received at storage capacitor CC6, which smoothes out the voltage before it is passed to charging circuitry 92. The charging circuitry 92 is used for controlling the charge of battery source 93. To prevent VOUT exceeding a predetermined value, a Zener diode or another suitable voltage clamp circuit can be connected to capacitor C6.

“FIG. 10. shows the status of the transistor switches M6, M7, and M8 for energy receive, data transmit, and data receive modes. FIG. FIG. 10. The circuit in FIG. 9 will operate in energy receive mode. The circuit will turn switches M6 and M7 OFF and switch M8 ON. To turn M8 ON, capacitor C5 is connected with capacitor C4, which together with the inductance created by coil L2, form a resonant loop that tunes to the frequency of the RF signal (83) sent from the external control unit 12. For example, f1 could be around 80 kHz.

“The circuit shown in FIG. 9 can also be used in data transmit mode while charging, by using back telemetry known Load Shift Keying. U.S. Application Ser. No. No. 12/354,406, filed January 15, 2009 during LSK. The impedance of FIG. 9 can be modulated by controlling transistor switch M9 with the transistor’s off-resistance providing necessary modulation. The change in impedance of the coil is reflected back into the external control 12 unit 12, which generates the RF signal 83. This reflection is then demodulated at 12 unit external to recover the transmitted data. This method of transmitting data can be used to communicate information relevant during charging of battery 93 in microstimulator. It includes the capacity of the battery and whether the external charger should be stopped.

“For FIG. 9 will operate in data receive mode. The circuit will turn switches M6 and M8 OFF and switch M7 ON. The resonant circuit’s tuning is governed by capacitor C4 and coil L2. The resonant circuit tunes to a higher frequency, f2 with capacitor C5 removed. This corresponds to the modulated radio signal 88? The external control unit 12 receives the RF data signal. (The external control device 12 that sends RF data signal number 88 to the microstimulator. The external control unit 12 that sends RF data signal 88 to the microstimulator can be either the same device or separate. Although the external control units 12 may include multiple devices, FIG. 12 shows the external control module 12 as a single device. 9 for ease of reference). For example, f2 could be approximately 125kHz. This can be a center frequency for the modulated data in RF signal 88′. If the RF signal number 88?, for example, A logic?0 might be generated when the RF signal 88? is modulated according to a Frequency Shift Keying protocol. A logic?1 might contain a frequency that is slightly lower than the center frequency (e.g. 121 kHz). A logic?1 might contain a frequency slightly lower than the center frequency (e.g. 121 kHz), while a logic?1 could contain a frequency slightly above the center frequency (e.g. 129 kHz). Despite the slight differences, this band or range of frequencies can still be considered a single frequency. Turning M7 ON grounded the resonant circuit. This provides an input to receiver that demodulates the received data. A differential input, as shown in FIG. 9, can be used to build the receiver. 9 or a single-ended, non-differential input.

“As further illustrated in FIG. The circuit in FIG. 10 is also shown. 9, the circuit of FIG. The resonant circuit will be tuned to the higher frequency of f2 by turning transistor M8 off. It will also broadcast an RF signal to the external control units 12 according to these conditions. The power source voltage Vs is supplied via transistor M6. A transmitter will modulate the data at transistor M7 in accordance to the tuning of its resonant circuit. The center of the data will be around 125 KHz. The data signal that is presented to transistor M7 when transmitting logic?0 might include a 121kHz signal or a signal of 129kHz when transmitting logic?1. A transmitter could also be coupled to transistor M6.”

“It is evident that the circuit of FIG. can be controlled by selectively controlling the states of the switches M6,M7,M8 and M9. 9 can operate in different modes. These modes can be invoked in a time-multiplexed fashion, e.g. a first mode may be followed by a second, depending on the application. Tuning allows for charging at a frequency f1 and data transmission at a frequency f2. The circuitry in FIG. 9 has been optimized for charging at lower frequencies (e.g. 80 kHz) than higher frequencies due to heat concerns. Higher frequencies, such as 125 kHz have been shown to allow for higher bandwidth and higher data rates. Like other tunable circuits described herein, FIG. 9 provides an optimized design for charging and telemetry that uses only one coil. Variable capacitors could be substituted for capacitors C4 or C5 in order to achieve similar tuning.

“It can be seen that the invention described in this document provides a voltage conversion circuit for use in an implantable device. It is, for example, an implantable microstimulator (or similar type of neural stimulationator), that is compact and efficient and offers a wide range output voltages or currents.

“It can also be seen that the invention provides a voltage convert circuit that eliminates the need for a network capacitors switched between parallel or series configurations, or any other configurations, in order to provide step up and drop voltage conversion functions.”

“It can also be seen that the invention contains an implantable device that has a single coil that can be tunable at different frequencies for charging or telemetry.”

“While the invention disclosed herein has been described using specific embodiments and their applications, many modifications and variations could still be made by those skilled in art without departing form the scope of the invention as set forth in its claims.”

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What is a software medical device?

The FDA can refer to software functions that include ” Software As a Medical Device” and “Software in a Medical Device(SiMD)”, which are software functions that are integral to (embedded in a) a medical device.

Section 201(h),?21 U.S.C. 321(h),(1) defines a medical device to be?an apparatus, implements, machine, contrivances, implant, in vitro regulator, or other similar or related articles, as well as a component or accessory. . . (b) is intended for diagnosis or treatment of disease or other conditions in humans or animals. (c) Is intended to alter the structure or function of human bodies or animals. To be considered a medical device, and thus subject to FDA regulation, the software must meet at least one of these criteria:

• It must be used in diagnosing and treating patients.
• It must not be designed to alter the structure or function of the body.

If your software is designed to be used by healthcare professionals to diagnose, treat, or manage patient information in hospitals, the FDA will likely consider such software to be medical devices that are subject to regulatory review.

Is Your Software a Medical Device?

FDA’s current oversight, which puts more emphasis on the functionality of the software than the platform, will ensure that FDA does not regulate medical devices with functionality that could be dangerous to patient safety. Examples of Device Software and Mobile Medical Apps FDA is focused on

• Software functions that aid patients with diagnosed mental disorders (e.g., depression, anxiety, and post-traumatic stress disorder (PTSD), etc.) by providing “Skill of the Day”, a behavioral technique, or audio messages, that the user can access when they are experiencing anxiety.
• Software functions that offer periodic reminders, motivational guidance, and educational information to patients who are recovering from addiction or smokers trying to quit;
• Software functions that use GPS location data to alert asthmatics when they are near high-risk locations (substance abusers), or to alert them of potential environmental conditions that could cause symptoms.
• Software that uses video and games to encourage patients to exercise at home.
• Software functions that prompt users to choose which herb or drug they wish to take simultaneously. They also provide information about interactions and give a summary of the type of interaction reported.
• Software functions that take into account patient characteristics, such as gender, age, and risk factors, to offer patient-specific counseling, screening, and prevention recommendations from established and well-respected authorities.
• Software functions that use a list of common symptoms and signs to give advice about when to see a doctor and what to do next.
• Software functions that help users to navigate through a questionnaire about symptoms and to make a recommendation on the best type of healthcare facility for them.
• These mobile apps allow users to make pre-specified nurse calls or emergency calls using broadband or cell phone technology.
• Apps that allow patients or caregivers to send emergency notifications to first responders via mobile phones
• Software that tracks medications and provides user-configured reminders to improve medication adherence.
• Software functions that give patients access to their health information. This includes historical trending and comparisons of vital signs (e.g. body temperature, heart rate or blood pressure).
• Software functions that display trends in personal healthcare incidents (e.g. hospitalization rates or alert notification rate)
• Software functions allow users to electronically or manually enter blood pressure data, and to share it via e-mail, track it and trend it, and upload it to an electronic or personal health record.
• Apps that offer mobile apps for tracking and reminders about oral health or tools to track users suffering from gum disease.
• Apps that offer mobile guidance and tools for prediabetes patients;
• Apps that allow users to display images and other messages on their mobile devices, which can be used by substance abusers who want to quit addictive behaviors.
• Software functions that provide drug interaction and safety information (side effects and drug interactions, active ingredient, active ingredient) in a report based upon demographic data (age and gender), current diagnosis (current medications), and clinical information (current treatment).
• Software functions that allow the surgeon to determine the best intraocular lens powers for the patient and the axis of implantation. This information is based on the surgeon’s inputs (e.g., expected surgically induced astigmatism and patient’s axial length, preoperative corneal astigmatism etc.).
• Software, usually mobile apps, converts a mobile platform into a regulated medical device.
• Software that connects with a mobile platform via a sensor or lead to measure and display electrical signals from the heart (electrocardiograph; ECG).
• Software that attaches a sensor or other tools to the mobile platform to view, record and analyze eye movements to diagnose balance disorders
• Software that collects information about potential donors and transmits it to a blood collection facility. This software determines if a donor is eligible to collect blood or other components.
• Software that connects to an existing device type in order to control its operation, function, or energy source.
• Software that alters or disables the functions of an infusion pump
• Software that controls the inflation or deflation of a blood pressure cuff
• Software that calibrates hearing aids and assesses sound intensity characteristics and electroacoustic frequency of hearing aids.

What does it mean if your software/SaaS is classified as a medical device?

SaaS founders need to be aware of the compliance risks that medical devices pose. Data breaches are one of the biggest risks. Medical devices often contain sensitive patient data, which is why they are subject to strict regulations. This data could lead to devastating consequences if it were to become unprotected. SaaS companies who develop medical devices need to take extra precautions to ensure their products are safe.

So who needs to apply for FDA clearance? The FDA defines a ?mobile medical app manufacturer? is any person or entity who initiates specifications, designs, labels, or creates a software system or application for a regulated medical device in whole or from multiple software components. This term does not include persons who exclusively distribute mobile medical apps without engaging in manufacturing functions; examples of such distributors may include the app stores.

Software As Medical Device Patenting Considerations

The good news is that investors like medical device companies which have double exclusivity obtained through FDA and US Patent and Trademark Office (USPTO) approvals. As such, the exit point for many medical device companies is an acquisition by cash rich medical public companies. This approach enables medical devices to skip the large and risky go-to-market (GTM) spend and work required to put products in the hands of consumers.

Now that we have discussed the FDA review process, we will discuss IP issues for software medical device companies. Typically, IP includes Patents, Trademarks, Copyrights, and Trade secrets. All of these topics matter and should be considered carefully. However, we will concentrate on patents to demonstrate how careless drafting and lack of planning can lead to problems, namely unplanned disclosures of your design that can then be used as prior art against your patent application.

In general, you should file patent application(s) as soon as practicable to get the earliest priority dates. This will help you when you talk to investors, FDA consultants, prototyping firms, and government agencies, among others. Compliance or other documents filed with any government agency may be considered disclosure to third parties and could make the document public. In general, disclosures to third parties or public availability of an invention trigger a one year statutory bar during which you must file your patent application. Failure to file your application within the required time frame could result in you losing your right to protect your invention.

The information from your FDA application may find its way into FDA databases, including DeNovo, PMA and 510k databases and FDA summaries of orders, decisions, and other documents on products and devices currently being evaluated by the FDA. Your detailed information may be gleaned from Freedom of Information Act requests on your application. This risk mandates that you patent your invention quickly.

When you patent your medical device invention, have a global picture of FDA regulatory framework when you draft your patent application. Be mindful of whether your software/SaaS application discusses the diagnosing and treating patients or affecting the structure or function of the body and add language to indicate that such description in the patent application relates to only one embodiment and not to other embodiments. That way you have flexibility in subsequent discussions with the FDA if you want to avoid classification of your software/SaaS/software as a medical device. In this way, if you wish to avoid FDA registration and oversight, you have the flexibility to do so.

An experienced attorney can assist you in navigating the regulatory landscape and ensure that you comply with all applicable laws. This area of law is complex and constantly changing. It is important that you seek legal advice if you have any questions about whether or not your software should be registered with FDA.

Patent PC is an intellectual property and business law firm that was built to speed startups. We have internally developed AI tools to assist our patent workflow and to guide us in navigating through government agencies. Our business and patent lawyers are experienced in software, SaaS, and medical device technology. For a flat fee, we offer legal services to startups, businesses, and intellectual property. Our lawyers do not have to track time as there is no hourly billing and no charges for calls or emails. We just focus on getting you the best legal work for your needs.

Our expertise ranges from advising established businesses on regulatory and intellectual property issues to helping startups in their early years. Our lawyers are familiar with helping entrepreneurs and fast-moving companies in need of legal advice regarding company formation, liability, equity issuing, venture financing, IP asset security, infringement resolution, litigation, and equity issuance. For a confidential consultation, contact us at 800-234-3032 or make an appointment here.