WO2011137168A1 - Medical device with self-adjusting power supply - Google Patents

Abstract

Techniques are described for dynamically adjusting a power supply voltage such that the power supply voltage is slightly higher than a required power supply voltage. In one example, a method includes detecting a first voltage at an output of a stimulation generator of a medical device, comparing the detected first voltage and a second voltage, and adjusting a supply voltage of the stimulation generator based on the comparison.

Description

MEDICAL DEVICE WITH SELF-ADJUSTING POWER SUPPLY

TECHNICAL FIELD

[0001] The disclosure relates to medical devices and, more particularly, to power supplies for medical devices.

BACKGROUND

[0002] Many electronic devices are powered by fixed power supply voltages. The output signals produced by these devices, however, are often time-varying voltages. The output circuitry of the device generates the time-varying output voltage by introducing a variable resistor, e.g., a transistor, between the power supply and the output load. The variable resistor causes a voltage drop across its terminals, and the remaining voltage is delivered to the output load. Some examples of output loads for various electronic devices include loudspeakers in the case of an audio amplifier, human tissue in the case of an implantable electrical stimulator, a motor in the case of a motor drive circuit, and a cable or antenna in the case of telecommunication transmitters.

[0003] When the voltage of the output signal is at or near the fixed voltage of the power supply, the voltage drop and the resulting power dissipated by the output circuit are minimal. However, when the voltage of the output signal is lower than the fixed voltage of the power supply, a significant portion of the power supply voltage may be absorbed by the output circuitry, e.g., the variable resistor. In other words, a significant portion of the power drawn from the power supply may be wasted by the output circuitry when there is a large difference between the voltage of the output signal and the fixed voltage of the power supply.

SUMMARY

[0004] In general, this disclosure describes techniques for dynamically adjusting a power supply voltage such that the power supply voltage is slightly greater than a power supply voltage required by output circuitry. Rather than apply a fixed voltage supply to a variable resistor as a power supply voltage, various techniques of this disclosure utilize electronic circuitry that dynamically adjusts the power supply voltage. The electronic circuitry may include a voltage converter and a peak detector. The voltage converter adjusts a power supply voltage such that the power supply voltage is slightly greater than a peak output voltage detected across a load. By adjusting the power supply voltage provided to the output circuitry in this manner, less power may be wasted by the output circuitry.

[0005] In one example, the disclosure is directed to a method comprising detecting a first voltage at an output of a stimulation generator of a medical device, comparing the detected first voltage and a second voltage, and adjusting a supply voltage of the stimulation generator based on the comparison.

[0006] In another example, the disclosure is directed to a device comprising a detector configured to detect a first voltage at an output of a stimulation generator of a medical device, a comparator configured to compare the detected first voltage and a second voltage, and a voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison.

[0007] In another example, the disclosure is directed to an implantable medical device comprising an electronic circuit. The electronic circuit comprises a detector configured to detect a first voltage at an output of a stimulation generator of a medical device, a comparator configured to compare the detected first voltage and a second voltage, and a voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison.

[0008] In another example, the disclosure is directed to an electronic circuit comprising means for detecting a first voltage at an output of a stimulation generator of a medical device, means for comparing the detected first voltage and a second voltage, and means for adjusting a supply voltage of the stimulation generator based on the comparison.

[0009] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0010] FIG. 1 is a block diagram illustrating an example PRIOR ART electronic circuit utilizing a fixed power supply.

[0011] FIG. 2 is a block diagram illustrating an example electronic circuit that may be used to implement the techniques of this disclosure.

[0012] FIG. 3 is a conceptual diagram illustrating an example peak detector.

[0013] FIG. 4 is a block diagram illustrating an example electronic circuit that may be used to implement the techniques of this disclosure.

[0014] FIG. 5 is a circuit diagram illustrating an example circuit for providing a self-adjusting power supply in accordance with techniques of this disclosure.

[0015] FIG. 6 is a circuit diagram illustrating another example circuit for providing a self-adjusting power supply in accordance with techniques of this disclosure.

[0016] FIG. 7 is a block diagram illustrating another example electronic circuit that may be used to implement various techniques of this disclosure.

[0017] FIG. 8 is a circuit diagram illustrating another example circuit for providing a self-adjusting power supply in accordance with various techniques of this disclosure.

[0018] FIG. 9 is a block diagram illustrating another example electronic circuit that may be used to implement the techniques of this disclosure.

[0019] FIG. 10 is a circuit diagram illustrating another example circuit for providing a self-adjusting power supply in accordance with various techniques of this disclosure.

[0020] FIG. 11 is a block diagram illustrating another example electronic circuit that may be used to implement certain techniques of this disclosure.

[0021] FIG. 12 is a flow diagram illustrating an example method for providing a self-adjusting power supply, in accordance with various techniques of this disclosure.

[0022] FIG. 13 is a schematic diagram illustrating a system including an implantable medical device in the form of an implantable electrical stimulation system.

[0023] FIG. 14 is a functional block diagram illustrating various example components of an implantable electrical stimulation system. DETAILED DESCRIPTION

[0024] FIG. 1 is a block diagram illustrating an example prior art electronic circuit utilizing a fixed power supply voltage to produce a power supply voltage.

Electronic circuit 20 depicts amplifier/controller 22 receiving an input signal that when amplified, is used to control variable resistor 24. One terminal of variable resistor 24, e.g., a transistor, is connected to a fixed power supply voltage, e.g., a battery. For conceptual purposes, the fixed power supply voltage in FIG. 1 is shown as a fixed + 5 volts (V), but may be any fixed voltage. The other terminal of variable resistor 24 is connected to a terminal of load 26. The input signal adjusts variable resistor 24 in order to produce a time-varying output voltage even though the circuit is powered by a fixed power supply voltage. It should be noted that FIG. 1 is a simplistic illustration presented to enhance the reader's

understanding of a fixed power supply voltage to produce a power supply voltage.

[0025] In this conceptual diagram, load 26 requires a + 3 V output across its terminals. In order to achieve a +3 V drop across the terminals of load 26 when load 26 is driven by a +5 V power supply voltage, +2V must be dropped across variable resistor 24. Amplifier/controller 22 receives an input signal and varies the resistance of variable resistor 24 in order to produce a +2V drop across its terminals. The power resulting from the +2V drop across variable resistor 24 is dissipated as heat, which may need to be removed from the circuit, thereby limiting the minimum size of the circuitry. For example, larger printed circuit boards, heat sinks, and/or fans may be required in the circuit design in order to prevent excess heat from building up. In addition to limiting the minimum size of the circuit, the power resulting from the +2V drop across variable resistor 24 (power equals (voltage)² divided by resistance) is simply wasted power. Such wasted power may reduce the overall performance of the battery or require increased battery capacity, e.g., a larger battery. A larger battery may increase the cost and size of the circuit or device.

[0026] FIG. 2 is a block diagram illustrating an example electronic circuit that may be used to implement various techniques of this disclosure. Like electronic circuit 20 of FIG. 1, electronic circuit 30 of FIG. 2 is connected to a fixed power supply voltage, e.g., a battery. For conceptual purposes, the fixed power supply voltage in FIG. 2 is shown as a fixed +5V, but may be any fixed voltage. In contrast to electronic circuit 20 of FIG. 1, and in accordance with various techniques of this disclosure, electronic circuit 30 of FIG. 2 includes peak detector 32 and voltage converter 34, collectively forming dynamic power adjustment unit 35. Fixed power supply voltage 36, peak detector 32, and voltage converter 34 form dynamic adjustment circuitry that may be used to reduce the amount of power wasted in circuit 30.

[0027] As seen in FIG. 2, the output voltage at load 38 is applied to peak detector 32. In some examples, the output voltage is continuously sampled and peak detector 32 detects its peak value. For example, in FIG. 2, the peak output voltage across load 38 is shown as +3V. Peak detector 32 outputs the peak voltage, e.g., +3V, to voltage converter 34. Voltage converter 34 converts the voltage supplied via fixed power supply 36, e.g., +5V, to a lower voltage, e.g., +4V, based on the peak voltage detected at output load 38 by peak detector 32, e.g., +3V. In other words, voltage converter 34 generates a power supply voltage, e.g., +4V, from the fixed power supply voltage, e.g., +5V, that is slightly higher than the required supply voltage, e.g., +3V. As compared to circuit 20 in FIG. 1, which employs fixed power supply circuitry, the dynamically adjusting power supply circuitry employed in FIG. 2, in accordance with certain techniques described in this disclosure, reduces the voltage drop across variable resistor 24 from +2V to +1V. As indicated above, the reduction in the voltage drop across variable resistor 24 reduces the amount of power wasted in the circuit.

[0028] The load impedance in FIG. 2 may represent an electrode/tissue interface at the output of a stimulation generator of a medical device. As such, in one example implementation, the circuit may be used to detect a voltage at an output of a stimulation generator of a medical device. An example system including an implantable medical device in the form of an implantable electrical stimulation system that may utilize various techniques of this disclosure is shown and described in more detail below with respect to FIG. 13. Also, example

components of such a system are shown and described in more detail below with respect to FIG. 14. [0029] In another example implementation, techniques described in this disclosure may be used for applications in which the electrical load is a motor, such as a DC Brushless Permanent Magnet Motor. DC motors may require different voltage and currents, depending on their operation. Once a mechanical load is increased, the current and the corresponding voltage applied to the motor may be increased, at least temporarily, to prevent the rotor from slowing down (which may lead to "commutation failure"). A high voltage demand may also occur during the start-up of the motor, especially for motors with heavier loads, such as compressors. Using various techniques of this disclosure, the voltage at the mechanical load may be detected using a peak voltage detector and a voltage converter may adjust the output power supply voltage to be slightly above the detected peak voltage.

[0030] Various techniques of this disclosure may also be utilized in

implementations in which it is desirable to fix the load voltage and vary the supply voltage. Such an implementation may be desirable when the supply voltage is derived from a time -varying source, e.g., wind or solar power systems, and the load is a battery to be charged. Because the techniques of this disclosure extract the necessary power from the source, e.g., a wind turbine or a photo-voltaic cell, and deliver the desired output voltage to the load, e.g., a fixed voltage battery, one or more circuits of this disclosure may act as a voltage regulator to assure that substantially the same amount of charge would be added to the battery even if the wind is blowing slowly on the fans of the turbine or if the sun is not shining very brightly on the photovoltaic cells.

[0031] FIG. 3 depicts a conceptual diagram illustrating an example peak detector. Peak detector 40 includes operational amplifier (op-amp) 42, diode 44, capacitor 46, and feedback circuit 48. Input signal Vi_N is applied to the anode of diode 44. Assuming that input signal V_IN is sufficient to forward bias (and thus turn on) diode 44, capacitor 46 charges to voltage V_IN - V-m (where V_TH is the threshold voltage of the diode, e.g., about 0.6 V). Diode 44 may prevent capacitor 46 from discharging if input signal Vi_N falls below the voltage on capacitor 46. Op-amp 42 may have a high input impedance and, as such, may prevent capacitor 46 from discharging. As seen in FIG. 3, the voltage at the non-inverting terminal (denoted by +) of op-amp 42, V+, is equal to the voltage stored on capacitor 46, or V_IN -

[0032] In the negative feedback configuration depicted in FIG. 3, the voltage at the non-inverting terminal (denoted by +) of op-amp 42, V+, is equal to the voltage at the inverting terminal (denoted by -) of op-amp 42, V-. In addition, as shown in FIG. 3, the inverting terminal is coupled to the output of op-amp 42 and hence the output voltage, VOU_T, of op-amp 42 equals the voltage at the inverting terminal, V-. Thus, the output voltage, VOU_T, of op-amp 42 equals voltage V+ at the non- inverting terminal of op-amp 42, which is equal to the voltage stored on capacitor 46, or V_IN - V_TH. In this manner, the peak detector of FIG. 3 outputs the peak voltage of input signal V_IN - V_TH

[0033] Numerous peak detectors may be used to perform the techniques described in this disclosure. For example, it may be desirable to add reset circuitry that would allow periodic discharge of capacitor 46 in order to detect an input signal V_IN with decreasing peak voltages. In other examples, it may be desirable to design a peak detector without an op-amp, thereby saving power and space. Again, the peak detector depicted in FIG. 3 is provided for conceptual purposes only and is not meant to limit the scope of this disclosure.

[0034] FIG. 4 is a block diagram illustrating an example electronic circuit that may be used to implement various techniques of this disclosure. FIG. 4 depicts an example circuit 50 that generates a feedback signal using a peak voltage and an output power supply voltage having opposite polarities. Comparator 52 generates the feedback signal (ON/OFF) by comparing negative peak voltage -V_PEA_K to positive output power supply voltage +V_PS. Voltage converter 54A uses the resulting signal to determine when to turn ON and OFF, similar to pulse width modulation techniques. In this manner, voltage converter 54A cycles power to the positive output power supply +V_PS so that it is only slightly above what is required by the load and rarely, if ever, is the positive output power supply +V_PS at full power. The circuit described in this disclosure shuts off voltage converter 54A (and voltage converter 54B) when a desired positive output power supply level is reached and turns on voltage converter 54A (and voltage converter 54B) when the positive output power supply level falls below a threshold. [0035] As seen in FIG. 4, fixed 5V voltage supply 56, e.g., a battery, supplies a single voltage converter, comprising voltage converter 54A and voltage converter 54B. It should be noted that a "fixed" voltage is fixed in the sense that it is not adjustable. However, a fixed voltage may sag under load such that its value may vary slightly. The single voltage converter generates the output power to both output power supplies, i.e., VPS and -VPS. Voltage converter 54A generates positive output supply voltage VPS and voltage converter 54B generates negative output supply voltage -Vps. Amplifier 58 amplifies an input signal that controls variable resistors 60 and 62 to produce a time-varying voltage at the load impedance. The output voltage at RLOAD- is applied to negative peak detector 64. In other words, negative peak detector 64 detects a first voltage, e.g., a peak voltage, at the load impedance. It should be noted that the techniques of this disclosure control operation of a voltage converter based on a voltage detected at the load and not at the output of the voltage converter.

[0036] Load impedance RLOAD- and RLOAD+ may be the electrode and the tissue impedance seen at the output of a stimulation generator of a medical device, such as an external or implantable neurostimulator, muscle stimulator, or cardiac stimulator, but may be any load impedance. In such an implementation, the voltage at the load impedance may be determined by measuring between one of the electrodes of a selected electrode combination and a reference potential, e.g., electrodes on one or more leads or an electrode on a lead and an electrode on the housing of the medical device.

[0037] Negative peak detector 64 outputs negative peak voltage -VPEAK to comparator 52. Comparator 52 compares negative peak voltage -VPEAK, e.g., the detected first voltage, and positive output power supply voltage V_Ps, e.g., a second voltage, and generates a feedback signal that, when applied to voltage converter 54A, determines when to turn both positive voltage converter 54A and negative voltage converter 54B ON and OFF. That is, when the difference between negative peak voltage -V_PEAK and positive output power supply voltage V_Ps is above a threshold value, comparator 52 turns ON positive voltage converter 54A and negative voltage converter 54B, which in turn, restores positive output power supply voltage VPS and negative output power supply voltage -VPS. In this manner, voltage converter 54A adjusts the supply voltage based on the comparison of the detected first voltage and the second voltage. It should be noted that the amount of time that the voltage converter is ON or OFF, i.e., the duty cycle of the voltage converter, is variable and depends on the voltage detected at the load.

[0038] As described above, FIG. 4 generates a feedback signal from the comparison of negative peak voltage -V_PEA_K to positive output voltage +V_PS. FIG. 5 illustrates an example circuit which may be used to implement the techniques shown in FIG. 4. An alternate example circuit, such as shown and described below with respect to FIG. 6, may generate the feedback signal from the comparison of a positive peak voltage +V_PEA_K to the negative output voltage -V_PS, and the resulting comparison signal may be used to determine when to turn the voltage converter ON and OFF. In both cases, once turned ON, the same voltage converter generates the output power to both supplies, i.e., +V_PS and -V_PS. One advantage of being able to select either a positive peak voltage +V_PEA_K or a negative peak voltage - V_PEA_K may be robust operation because regulation based on the supply side with the greatest demand (positive or negative) ensures that sufficient supply voltage is present for both sides of the supply.

[0039] FIG. 5 depicts an example circuit for providing a self-adjusting power supply in accordance with techniques of this disclosure. The circuitry depicted in FIG. 5 may be used to implement the block diagram shown in FIG. 4. The example circuitry of FIG. 5 utilizes a boost voltage converter in order to generate a power supply that is slightly higher than the required supply voltage. As will be described in more detail below, negative peak voltage -V_PEA_K is compared to the positive output power supply voltage V_PS and a voltage converter uses the resulting comparison signal in order to determine when to turn ON and OFF. Once turned on, the same voltage converter generates the output power to both supplies, i.e.,

[0040] Integrated circuit (IC) 70, a micropower step-up DC/DC converter, may be, for example, an LT^® 1615, available from Linear Technologies of Milpitas, California. IC 70 attempts to maintain a voltage (V_X) of 1.23 V on its feedback (FB) pin (pin 3). When the power supply voltage decreases on input supply (V_IN) pin 5 of IC 70, it causes V_X to also decrease. Once voltage V_X decreases below a threshold value on pin 3, IC 70 closes its internal power switch (SW) coupled to pin 1. Closing the switch coupled to pin 1 draws current from power source, e.g., battery, labeled "5 V" in FIG. 5, to inductor LI . After a period of time (determined by the internal circuitry of IC 70), IC 70 opens the internal power switch and current flowing into inductor LI is forced on the output capacitor C2 via diode Dl . The current flowing through inductor LI decreases, which then turns the power switch on once again, thereby causing the current flowing through inductor LI to increase. IC 70 then opens the internal power switch, thereby forcing the current flowing into inductor LI onto output capacitor C2. This process continues until the voltage stored on output capacitor C2 reaches Vx.

[0041] In accordance with certain techniques of this disclosure, resistor R₃, diode Dp, and capacitor Cp are added in order to build a peak detector that will regulate the output voltage Vps. In contrast to the conceptual peak detector shown in FIG. 3, voltage VLOAD is applied to the cathode of diode D_P. Thus, when voltage VLOAD is sufficiently below the voltage at the anode of diode D_P (about 0.6-0.7 V), diode Dp turns on, allowing capacitor Cp to charge. In this manner, D_P turns on and charges capacitor Cp to the peak negative voltage, -VPEAK, of voltage VLOAD, thereby forming a peak negative voltage detector. Diode Dp prevents capacitor Cp from discharging. Peak negative voltage -VPEAK is applied to the feedback pin (pin 3) of IC 70 via resistor R₃, which provides the operation described above with respect to FIG. 2.

[0042] In some examples, the values of the resistors Ri, R₂ and R₃ should be selected in order to provide for the desired headroom voltage left on the power supply for any given output voltage. Headroom voltage refers to the minimum voltage difference between the supply voltage generated by the voltage converter and the output voltage to ensure proper operation of the voltage converter and, hence, reliable regulation of the output voltage level. Determining the values of resistor R_{l s} R₂ and R₃ may be achieved by imposing the following requirement:

(1) VpSExp ⁼ VpEAK + VHEADROOM,

where VPSE_XP is the expected power supply voltage, VPEAK is the peak output voltage, and VHEADROOM is the desired headroom. [0043] Using Ohm's Law and Kirchhoff's Current Law, the following equations may be obtained from FIG. 5 :

(2) I₃ = ( 1.23 + VPEAK ) / R3

(3) h = ( +5.0 - 1.23 ) / R₂

(4) Ii = - h

where Ii is the current through resistor R_ls I₂ is the current through resistor R₂, and L is the current through resistor R₃.

[0044] For a given range of the output voltage and a set headroom requirement, the values of Rl, R2 and R3 may be determined either by a multi-dimensional optimization algorithm or by trial and error. Optimization may be carried out by minimizing the following function in order to determine the values of Rl, R2 and

R3:

(6) Min f(R_b R₂, R₃) =∑ [\_PSExp - V_PS] ²

[0045] For example, for a headroom voltage of V_HEA_DROO_M = 2 V and a power supply voltage range of 0 < V_PEA_K≤ 10 Volts, the following resistors values were determined using the optimization algorithm described above: Ri = 61 kQ, R₂ = 500 kQ, and R₃ = 61 kQ.

[0046] FIG. 6 depicts another example circuit for providing a self-adjusting power supply in accordance with techniques of this disclosure. The example circuitry of FIG. 6 utilizes charge pump voltage converter circuitry in order to generate a power supply that is slightly higher than the required supply voltage. As will be described in more detail below, positive peak voltage V_PEA_K is compared to the negative output power supply voltage -V_PS and the resulting comparison signal is used to determine when to turn the voltage converter ON and OFF. Once turned on, the same voltage converter generates the output power to both supplies, i.e., V_Ps and -

[0047] The charge pump based voltage converter is shown to the left of the dashed line in FIG. 6. In this example, operation of the voltage converter is controller by integrated circuit U19. IC U19, a switched capacitor voltage converter, may be for example, an LTC® 1044, available from Linear Technologies of Milpitas,

California. An internal oscillator of IC U19 produces timing signals that open and close two pairs of internal switches to force the input voltage from pin 8 (VCC) of IC U19 onto capacitors C21 , C22, C24, C32, and C23 for the positive supply voltage, VPS, and onto the capacitors C30, C26, C25, C27 and C28 for the negative supply voltage, -VPS. Because the positive supply voltage on holding capacitor C31 is the sum of the voltages on capacitors C21 , C22, and C32, the positive supply voltage VPS is approximately equal to three times the input voltage at pin 8 (VCC) of IC U19. Similarly, because the negative supply voltage on holding capacitor C29 is the sum of the voltages on capacitors C25, C28, and C30, the negative supply voltage is approximately equal to negative three times that of the input voltage at pin 8 (VCC) of IC U19.

[0048] In accordance with certain techniques of this disclosure, diode D_P and capacitor Cp are added to the circuitry on the right of the dashed line in FIG. 6 in order to build a peak detector that will regulate the power supply voltage V_Ps. The peak detector formed by diode D_P and capacitor Cp measures the peak voltage, VPEAK, of the output voltage, VLOAD- Peak voltage VPEAK is fed back to pin 4 of comparator 80, e.g., a LMC7211BIM CMOS comparator, through resistor R₄i. Once the absolute value of the negative power supply voltage, |-VPS|, falls below a threshold value equal to V_PEAK + VREADROOM, comparator 80 turns on transistor Q₃, thereby energizing the switched capacitor voltage converter, IC U19. Once energized, IC U19 increases the voltage on holding capacitors C31 and C29, thereby restoring both the negative and the positive power supply voltages.

[0049] In order to function most effectively, the circuitry of FIG. 6 incorporates feedback. The feedback voltage is controlled by the values of resistors R₅₃, R₅₄, R52 and R29, R₄i, and R₄₂. Resistors R₅₃ and R₅₄ form a voltage divider and provide a voltage reference, Vx, for comparator 80. The values of resistors R₅₃ and R₅₄ can be determined using the equation below:

(7) Vx = -V_B * R54 / ( R54 + R₅₃)

where Vx is a reference voltage for comparator 80, and -VB is a battery voltage, e.g., -5V. [0050] Values of resistors R52, R41, and R42 should be selected in order to provide for the desired headroom voltage left on the power supply for any given output voltage. Again, this can be achieved by imposing the following requirement:

(8) VpsExp ⁼ pEAK + VREADROOM

where V_PS_EXP is the expected power supply voltage, V_PEA_K is the positive peak output voltage, and V_HEA_DROO_M is the desired headroom.

[0051] Using Ohm's Law and Kirchhoff's Current Law, the following equations may be obtained:

(9) I₅2_//29 = ( V_B - Vx ) / R₅₂

(10) I₄1 = (VPEAK - Vx ) / R41

(11) I42 = I41 + I52

(12) VPS = - (Vx - R42 * I42)

where I₄₁ is the current through R4i, I₄₂ is the current through R42, and I52//29 is the current through R52//29.

[0052] For a given range of the output voltage and a set headroom requirement, the values of R₅₂, R41, R42 may be determined, for example, by a multi-dimensional optimization algorithm or by trial and error. Optimization may be carried by minimizing the following function:

(13) Min f (R₅₂//29, R41, R42) =∑ [VPSEX_P - VPS]²

For example, for a headroom of V_HEA_DROO_M = 4.2 V and a power supply voltage range of 0 < V_PEA_K≤ 10 V, the following resistors values were determined using the optimization algorithm described above:

R52//29 = 500 kQ (formed by a parallel connection of two 1 ΜΩ resistors, R₅₂ and R₂₉)

R4i = 320 kQ (standard resistor value of 330 kQ was used instead) R42 = 320 kQ (standard resistor value of 330 kQ was used instead)

[0053] FIG. 7 is a block diagram illustrating another example electronic circuit that may be used to implement various techniques of this disclosure. In contrast to the circuit described above with respect to FIGS. 5 and 6, FIG. 7 depicts circuit 90 that generates a feedback signal using a peak voltage and an output power supply voltage having the same polarity. In FIG. 7, comparator 92 generates a feedback signal (ON/OFF) by comparing positive peak voltage +V_PEA_K to positive output voltage +Vps. Voltage converter 94 A uses the resulting comparison signal in order to determine when to turn ON and OFF.

[0054] As seen in FIG. 7, fixed 5 V voltage 96, e.g., a battery or output of a voltage regulator, supplies a single voltage converter, comprising voltage converter 94A and voltage converter 94B. The single voltage converter generates the output power to both supplies. Voltage converter 94A generates positive output supply voltage V_PS and voltage converter 94B generates negative output supply voltage - Vps. Amplifier 98 amplifies an input signal in order to control variable resistors 100 and 102 and thus produce a time -varying output voltage.

[0055] In the example circuit of FIG. 7, the output voltage at R_LOA_D+ is applied to positive peak detector 104. In other words, positive peak detector 104 detects a first voltage, e.g., a peak voltage. Positive peak detector 104 outputs positive peak voltage +V_PEA_K to comparator 92. Comparator 92 compares positive peak voltage +V_PEA_K, e.g., the detected first voltage, and positive output power supply voltage V_PS and generates a feedback signal that, when applied to voltage converter 94A, determines when to turn voltage converter 94A (and voltage converter 94B) ON and OFF. That is, when the difference between positive peak voltage +V_PEA_K and positive output power supply voltage V_PS is above a threshold value, comparator 92 turns on voltage converter 94A (and voltage converter 94B), which in turn, restores positive output power supply voltage V_Ps. In this manner, voltage converter 94A adjusts the supply voltage based on the comparison of the detected first voltage and the second voltage.

[0056] A single comparator is used in the block diagram depicted in FIG. 7. As such, when the difference between positive peak voltage +V_PEA_K and positive output power supply voltage V_PS is above a threshold value, comparator 92 not only turns on voltage converter 94 A, but also voltage converter 94B. Turning on voltage converter 94B boosts negative output power supply voltage -V_PS.

[0057] As described above, FIG. 7 generates a feedback signal from the comparison of positive peak voltage V_PEA_K to positive output voltage +V_PS.

Although not depicted, an alternate example circuit may generate the feedback signal from the comparison of a negative peak voltage -V_PEA_K to the negative output voltage -VPS, and the resulting comparison signal may be used to determine when to turn the voltage converter ON and OFF. In both cases, once turned ON, the same voltage converter generates the output power to both supplies, i.e., +VPS and -Vps. One advantage of such a circuit may be a robust operation, given that the measurement of the supply and the demand (peak voltage) are made from the same side of the output supply. When the electrical load draws equal current from both supplies, such as a loudspeaker driven by a sinusoidal signal, the regulation of the power supply can be done using either the positive or the negative supply, since both supplies would be depleted at roughly the same rate. However, when the load draws uneven amounts of current from the supplies, such as a servo motor, then regulation may be improved if the feedback signal is obtained from the same supply side as the output voltage is measured from. The circuitry shown on FIG. 7 may accomplish this goal by monitoring the load and regulating the supply on the positive side, with the assumption that the load is generally heavier on the positive side.

[0058] FIG. 8 depicts another example circuit for providing a self-adjusting power supply in accordance with various techniques of this disclosure. FIG. 8 is a schematic diagram of one example circuit that may be used to implement the techniques depicted and described above with respect to the block diagram shown in FIG. 7. The circuit shown in FIG. 8 is similar to the circuit shown and described above with respect to FIG. 5. Unlike the circuit shown in FIG. 5, however, the example circuit of FIG. 8 generates a feedback signal using the peak voltage and the output power supply voltage having the same polarity (both are positive in FIG. 8).

[0059] The circuit of FIG. 8 includes a peak detector, formed by diode D_P and capacitor Cp, which measures the positive peak voltage, VPEAK, of the output voltage, VLOAD- Positive peak voltage VPEAK is applied to comparator 110 via a voltage divider formed by resistor Rl 12 (100 kQ) and resistor Rl 14 (680 kQ). Comparator 110 compares the positive peak voltage VPEAK to a reference voltage determined by a voltage divider comprising resistor R116 (100 kQ) and resistor Rl 18 (680 kQ). Once the positive power supply voltage, VPS, falls below a threshold value equal to VPEAK + VHEADROOM, comparator 110 turns on transistor Q₃, thereby energizing the switched capacitor voltage converter, IC U19. Once energized, IC U19 increases the voltage on the holding capacitors (not shown), thereby restoring the power supply voltages +VPS and -VPS.

[0060] FIG. 9 is a block diagram illustrating another example electronic circuit that may be used to implement various techniques of this disclosure. In FIG. 9, unlike the circuit shown in FIG. 6, for example, the positive and negative supply circuits in circuit 130 of FIG. 9 are completely separate. Circuit 130 of FIG. 9 includes two peak voltage detectors, namely peak voltage detector 132 and peak voltage detector 134, for separately detecting peak voltages for the positive and negative sides, respectively. Further, the circuit of FIG. 9 includes two separate voltage converters, namely voltage converter 136 and voltage converter 138, for generating an output voltage for the positive and negative sides, respectively. Fixed DC voltage supply 140, e.g., a 5V battery or the output of a voltage regulator, supplies both positive voltage converter 136 and negative voltage converter 138. Voltage converter 136 generates positive output supply voltage VPS and voltage converter 138 generates negative output supply voltage -Vps.

[0061] Amplifier 142 amplifies an input signal in order to control variable resistors 144 and 146 and thus produce a time -varying output voltage. For the positive side, the output voltage at RLOAD+ is applied to positive peak detector 132. In other words, positive peak detector 132 detects a first voltage, e.g., a peak voltage.

Positive peak detector 132 outputs positive peak voltage +V_PEAK to comparator 148. Comparator 148 generates the feedback signal for the positive side by comparing positive peak voltage +VPEAK, e.g., the detected first voltage, to positive output voltage +VPS, e.g., a second voltage. Voltage converter 136 uses the resulting signal from comparator 148 in order to determine when voltage converter 136 for the positive side should turn ON and OFF. When the difference between positive peak voltage +VPEAK and positive output power supply voltage VPS is above a threshold value, comparator 148 turns on positive voltage converter 136, which in turn, restores positive output power supply voltage V_Ps. In this manner, voltage converter 136 adjusts the supply voltage based on the comparison of the detected first voltage and the second voltage. [0062] Similarly, for the negative side, the output voltage at R_LOA_D- is applied to negative peak detector 134. Negative peak detector 134 outputs negative peak voltage -V_PEA_K to comparator 150. Comparator 150 generates the feedback signal for the negative side by comparing negative peak voltage -V_PEA_K to negative output voltage -V_PS. Voltage converter 138 uses the resulting signal from comparator 150 in order to determine when voltage converter 138 for the negative side should turn ON and OFF. When the difference between negative peak voltage -V_PEA_K and negative output power supply voltage -V_Ps is above a threshold value, comparator 150 turns on negative voltage converter 138, which in turn, restores negative output power supply voltage -V_PS. Thus, like the positive side, the negative side of FIG. 9 also detects a voltage, e.g., negative peak voltage -V_PEA_K, at load

impedance, e.g., an output of a stimulation generator of a medical device, compares the detected voltage and another second voltage, e.g., negative output voltage -V_PS, and adjusts a supply voltage based on the comparison.

[0063] The example circuit shown in FIG. 9 may provide several advantages. For example, the circuit in FIG. 9 may be useful in applications in which a load draws uneven power from two supplies, e.g., a higher power draw from the positive side then the negative side. Such an application may benefit from separate adjustment of the positive and negative sides. In addition, the circuit in FIG. 9 may preserve battery power by operating both the positive side and the negative side under optimal conditions.

[0064] FIG. 10 depicts another example circuit for providing a self-adjusting power supply in accordance with various techniques of this disclosure. The circuit depicted in FIG. 10 may be used to implement the block diagram shown in FIG. 9. FIG. 10 includes two peak voltage detectors for separately detecting peak voltages for the positive and negative sides. A first peak detector is formed by diode D33 and capacitor ClOl, which measures the positive peak voltage, V_PEA_K, of the output voltage, V_LOA_D- A second peak detector is formed by diode D38 and CI 02, which measures the negative peak voltage, -V_PEA_K, of the output voltage, V_LOA_D- [0065] Comparator 153 compares the positive peak voltage V_PEA_K to a reference voltage determined by a voltage divider comprising resistor R75 (390 kQ) and resistor R8 (100 kQ). Once the positive power supply voltage, V_PS, falls below a threshold value equal to V_PEA_K + V_HEA_DROO_M, comparator 153 turns on transistor Q₇, thereby energizing the switched capacitor voltage converter, IC U20. Once energized, IC U20 increases the voltage on holding capacitor C43, thereby restoring the positive power supply voltage +V_Ps.

[0066] Similarly, comparator 154 compares the negative peak voltage -V_PEA_K to a reference voltage determined by a voltage divider comprising resistor R81 (100 kQ) and resistor R82 (100 kQ). Once the negative power supply voltage, -V_PS, falls below a threshold value equal to -V_PEA_K + V_HEA_DROO_M, comparator 154 turns on transistor Qg, thereby energizing the switched capacitor voltage converter, IC U21. Once energized, IC U21 increases the voltage on holding capacitor C74, thereby restoring the negative power supply voltages -V_PS.

[0067] FIG. 11 is a block diagram illustrating another example electronic circuit that may be used to implement certain techniques of this disclosure. Circuit 160 in FIG. 11 may be used to construct a constant current source over a load impedance. The load impedance may be, for example, an electrode and the tissue impedance seen at the output of a stimulation generator of a medical device. In other examples, the load impedance may be a motor.

[0068] FIG. 11 depicts fixed DC voltage supply 161, e.g., a battery, providing power to voltage converter 162. In order to maintain a constant current over load impedance R_LOA_D, voltage converter 162 turns ON and OFF based on a signal from comparator 164. In some example configurations, comparator 164 may be an op- amp that does not utilize negative feedback. A sense resistor, RS_ENS_E, is included in circuit 160 and when the voltage drop across the sense resistor exceeds the value of input signal V_IN, comparator 164 signals voltage converter 162 to turn OFF. In other words, voltage converter 162 turns OFF if current I_LOA_D through load impedance R_LOA_D is greater than V_IN / RS_ENS_E- In this manner, the circuit of FIG. 11 maintains a constant current over load impedance R_LOA_D- Sense resistor RS_ENS_E may have a value of about 0.1 Ω to about 1 Ω, although higher values may be used if the load current is very low, and smaller resistor values may be used if the load current is high. One advantage of the configuration of FIG. 11 is that it may use less power than other op-amp based designs. [0069] In some example implementations, the circuit of FIG. 1 1 may be utilized by a stimulation generator of a medical device to produce a controlled current pulse. In other implementations, the circuit of FIG. 1 1 may be utilized by a stimulation generator of a medical device to produce a controlled voltage pulse.

[0070] FIG. 12 is a flow diagram illustrating an example method for providing a self-adjusting power supply, in accordance with various techniques of this disclosure. A peak detector detects a first voltage, e.g., a peak voltage or a voltage across a sense resistor, at a load impedance (200). The load impedance may be, for example, an output of a stimulation generator of a medical device. In other example implementations, the load impedance may be a motor, such as a DC brushless permanent magnet motor. After detecting the first voltage, a comparator compares the detected first voltage and a second voltage (205). The second voltage may be, for example, positive output supply voltage V_PS, negative output supply voltage -V_PS, or an input voltage, e.g., V_IN of FIG. 10. Based on the comparison of the first and second voltages, a voltage converter adjusts the supply voltage in order to restore the output power supply voltage, e.g., V_Ps or -V_Ps (210).

[0071] In some examples, detecting a first voltage at an output of a stimulation generator of a medical device comprises detecting a peak output voltage, wherein the second voltage is the supply voltage, and wherein adjusting a supply voltage based on the comparison comprises turning on a voltage converter.

[0072] In one example, the peak output voltage is a negative peak output voltage and the supply voltage is a positive output voltage. In another example, the peak output voltage is a positive peak output voltage, and the supply voltage is a negative output voltage. In another example, the peak output voltage is a negative peak output voltage, and the supply voltage is a negative output voltage. In another example, the peak output voltage is a positive peak output voltage, and the supply voltage is a positive output voltage.

[0073] In some examples, the supply voltage is a first supply voltage, and the voltage converter is a first voltage converter. In such examples, the method may further include detecting a negative peak output voltage, comparing the detected negative peak output voltage and a second supply voltage, and adjusting the second supply voltage from a second voltage converter based on the comparison. In some examples, the second supply voltage is a negative output voltage.

[0074] FIG. 13 is a schematic diagram illustrating a system 310 including an implantable medical device in the form of an implantable electrical stimulation system that may utilize the various dynamically adjusting power supply techniques described in this disclosure. FIG. 13 illustrates an example patient 312 having an IMD 314 (e.g., a stimulator) implanted in his or her body. While patient 312 is depicted as a human being in FIG. 13, patient 312 is not necessarily a human being. For example, patient 312 may be another animal. IMD 314 forms one part of a medical device system 310, which also includes an external programmer 320. As shown in FIG. 13, system 310 further includes a pair of stimulation leads 316A, 316B implanted within a patient 312 and coupled to IMD 314. Stimulation leads 316 A, 316B may carry one or more electrodes through which IMD 314 delivers stimulation to a target tissue site within patient 312.

[0075] External programmer 320 may be a patient programmer or a clinician programmer, for example. A patient programmer may permit a patient to select particular neurostimulation therapy programs specifying parameters for delivery of neurostimulation, such as electrical stimulation voltage or current amplitude, pulse width, pulse rate, electrode configuration, duty cycle, or the like. The patient programmer may permit a patient to select individual programs, or groups of programs, or possibly adjust some of the parameters associated with the programs.

[0076] The patient programmer may be configured to permit the patient to control or adjust only a limited subset of the therapy parameters, rather than all of such therapy parameters, e.g., for safety reasons or simplicity in patient programmer operation. For example, the patient programmer may be configured to permit the patient amplitude, pulse width, or pulse rate adjustments to be made only within a limited range, or to permit only particular sets of electrode configurations to be selected by the patient. In contrast, a clinician programmer may be configured for use by a clinician or other caregiver, and permit a clinician to control or adjust a larger, and perhaps complete, set of therapy parameters, relative to the limited set of parameters adjustable via the patient programmer. [0077] As shown in FIG. 13, leads 316A, 316B (collectively "leads 316") are implanted adjacent a spinal cord 318 of patient 312, e.g., for spinal cord stimulation (SCS) to alleviate pain. However, the various techniques described in this disclosure are applicable to systems including an IMD 314 coupled to leads implanted to target any of a variety of target locations within patient 312, such as leads carrying electrodes located proximate to spinal cord 318, pelvic nerves, peripheral nerves, the stomach or other gastrointestinal organs, or within the brain of a patient. In some examples, leads 316 may be coupled to lead extensions or lead adaptors.

[0078] In the example of FIG. 13, stimulation energy is delivered from IMD 314 via a stimulation generator (shown and described below with respect to FIG. 14) to spinal cord 318 of patient 312 via one or more electrodes carried by axial leads 316A and 316B implanted within the patient. The load impedances described above, e.g., load impedance R_LOA_D- and R_LOA_D+, may be the electrode and the tissue impedance seen at the output of the stimulation generator of IMD 314. In one example implementation, the various circuits described above may be used to detect a voltage at the output of the stimulation generator.

[0079] In various applications, such as spinal cord stimulation (SCS), the adjacent implantable leads 316 may have longitudinal axes that are substantially parallel to one another. Various combinations of electrodes carried by the leads 316 may be used to deliver electrical stimulation, including combinations of electrodes on a single lead or combinations of electrodes on both leads. Also, in some examples, electrodes may be carried by paddle leads in which an array of electrodes may be arranged in a two-dimensional pattern, e.g., as columns or rows of electrodes, on a common planar lead surface.

[0080] For leads or other electrode arrays, electrodes may be formed as any of a variety of electrodes such as ring electrodes, segmented electrodes, needle electrodes, pad electrodes, or the like. In general, the term "electrode array" may refer to electrodes deployed on axial leads, paddle leads, or other lead

configurations.

[0081] In the example of FIG. 13, leads 316 carry electrodes that are implanted adjacent to the target tissue of spinal cord 318. In particular, leads 316 may be implanted in the epidural space adjacent spinal cord 318, and coupled to IMD 314. In the example of FIG. 13, stimulation energy may be delivered to spinal cord 318 to eliminate or reduce pain perceived by patient 312. However, IMD 314 may be used with a variety of different therapies, such as peripheral nerve stimulation (PNS), peripheral nerve field stimulation (PNFS), deep brain stimulation (DBS), cortical stimulation (CS), pelvic floor stimulation, gastric stimulation, and the like. The stimulation may be configured to alleviate a variety of symptoms or conditions such as chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, or gastroparesis. The stimulation delivered by IMD 314 may take the form of stimulation pulses or continuous waveforms, and may be characterized by controlled voltage levels or controlled current levels, as well as pulse width and pulse rate in the case of stimulation pulses.

[0082] The stimulation energy may be delivered via selected combinations of electrodes carried by one or both of leads 316. The target tissue may be any tissue affected by electrical stimulation energy, such as electrical stimulation pulses or waveforms. Such tissue may include nerves, nerve branches, smooth muscle fiber, and skeletal muscle fiber. In the example illustrated by FIG. 13, the target tissue is spinal cord 318. Stimulation of spinal cord 318 may, for example, prevent pain signals from traveling thorough the spinal cord and to the brain of the patient. Patient 312 may perceive the interruption of pain signals as a reduction in pain and, therefore, efficacious therapy.

[0083] With reference to FIG. 13, a user, such as a clinician, physician or patient 312, may interact with a user interface of external programmer 320 to program IMD 314 or retrieve from IMD 314 information regarding operation of IMD 314. Programming of IMD 314 may refer generally to the generation and transfer of commands, programs, or other information to control the operation of the IMD 314. For example, programmer 320 may transmit programs, parameter

adjustments, program selections, group selections, or other information to control the operation of IMD 314, e.g., by wireless telemetry. Parameter adjustments may refer to initial parameter settings or adjustments to such settings. A program may specify a set of parameters that define stimulation. A group may specify a set of programs that define different types of stimulation, which may be delivered simultaneously using pulses with independent amplitudes or on a time-interleaved basis.

[0084] As indicated above, programmer 320 may be a clinician programmer or a patient programmer. An example of a commercially available clinician

programmer is the Medtronic N'Vision® Programmer Model 8840, marketed by Medtronic, Inc., of Minneapolis, Minnesota. An example of a commercially available patient programmer is the Medtronic myStim® Programmer, marketed by Medtronic, Inc. In some cases, external programmer 320 may be a physician or clinician programmer if it is primarily intended for use by a physician or clinician. In other cases, external programmer 320 may be a patient programmer if it is primarily intended for use by a patient.

[0085] In general, a physician or clinician programmer may support selection and generation of programs or parameters by a clinician for use by IMD 314. A clinician programmer may permit a clinician to control or adjust a larger set of therapy parameters than a patient programmer allows a patient to adjust. For example, a clinician programmer may allow a clinician to define new therapy programs or therapy parameter sets, or to modify parameters of an existing therapy program within a wide range. In contrast, a patient programmer may only allow a patient to select among predetermined therapy programs or to modify one or more therapy parameters within a range defined by the physician and programmed in the patient programmer. In some examples, a patient programmer may be configured to be portable and carried by patient 312 during a daily routine. In some examples, a medical device system 310 may include both a patient programmer and a clinician programmer, which may enable a clinician to program IMD 314 and/or the patient programmer and may allow patient 312 some control over his or her therapy.

[0086] IMD 314 may be implanted in patient 312 at a location minimally noticeable to the patient. Alternatively, IMD 314 may be external to patient 312 and coupled to implanted leads via a percutaneous extension. For spinal cord stimulation (SCS), as an example, IMD 314 may be located, among other locations, in the lower abdomen, lower back, or other location to secure the stimulator. Leads 316 may be tunneled from IMD 314 through tissue to reach the target tissue adjacent to spinal cord 318 for stimulation delivery. At distal portions of leads 316 are one or more electrodes (not shown) that transfer stimulation energy from the lead to the tissue. The electrodes may be electrode pads on a paddle lead, circular (i.e., ring) electrodes, surrounding the body of leads 16, segmented electrodes arranged at different axial and rotational positions around a lead, conformable electrodes, cuff electrodes, or any other type of electrodes capable of forming unipolar, bipolar or multipolar electrode configurations. In general, segmented electrodes arranged at selected axial and rotational positions at the distal ends of leads 316 will be described for purposes of illustration.

[0087] In the example of FIG. 13, each of the electrode combinations specifies a combination of electrodes arranged along lengths of two or more leads. If each lead 316 includes four ring electrodes, then the leads can be viewed as having four axial positions or levels. For segmented electrodes, an electrode may occupy a rotational arc at a given axial position of the lead. In some cases, the rotational arc may be similar to a portion of a ring electrode. For example, instead of a ring electrode that extends 360 degrees around a lead body, three, separate ninety degree segments could be provided to form three segmented electrodes at a given axial position along the length of the lead. Hence, two or more segmented electrodes may be provided at the same axial position but at different, non- overlapping rotational positions. Alternatively, a single segmented electrode could be provided at each of multiple axial levels. In general, in each case, a segmented electrode or electrode segment may have a dimension that spans only a portion of the circumference of the lead, unlike a ring electrode which generally extends around the entire circumference.

[0088] An electrode combination may include combinations of electrodes on the same lead or multiple leads, as well as one or more electrodes on a housing of IMD 314 in some cases. In each case, some electrodes in an electrode combination may form anodes while other electrodes form cathodes, establishing paths for flow of electrical stimulation current relative to an anatomical target such as spinal cord nerve tissue at a desired position on the spinal cord. As an example, for SCS, stimulation may be delivered in the vicinity of the T7, T8 and T9 vertebrae, although other positions on the spinal cord are possible. In a current-based system, electrodes may be selected to form anodes or cathodes coupled to regulated current sources and sinks, respectively.

[0089] FIG. 14 is a functional block diagram illustrating various components of IMD 314 of FIG. 13. In the example illustrated in FIG. 14, IMD 314 includes a processor 324, memory 326, stimulation generator 330, telemetry circuit 328, power source 332, and dynamic power adjustment circuitry 334. Dynamic power adjustment circuitry 334 represents the various circuits described above which dynamically adjust a power supply voltage such that the power supply voltage is slightly greater than a power supply voltage required by output circuitry. Using various techniques of this disclosure, dynamic power adjustment circuitry 334 may detect a first voltage at an output of stimulation generator 330, compare the detected first voltage and a second voltage, and adjust a supply voltage from power supply 332 based on the comparison.

[0090] Memory 326 may store instructions for execution by processor 324, stimulation therapy program data, sensor data, operational and status data, and any other electronic information regarding therapy or patient 312. Stimulation program data may include stimulation parameters transmitted from programmer 320, as well as programs defined by such parameters, and program groups. Some data may be recorded for long-term storage and retrieval by a user. Memory 326 may include separate memories for storing different types of data.

[0091] Processor 324 controls stimulation generator 330 to deliver electrical stimulation via electrode combinations formed by electrodes in one or more electrode arrays. For example, stimulation generator 330 may deliver electrical stimulation therapy via electrodes of one or more leads 316, e.g., as stimulation pulses or continuous waveforms. Stimulation generator 330 may include stimulation generation circuitry to generate stimulation pulses or waveforms and switching circuitry to switch the stimulation across different electrode

combinations, e.g., in response to control by processor 324. In particular, processor 324 may control the switching circuitry on a selective basis to cause stimulation generator 330 to deliver electrical stimulation to selected electrode combinations and to shift the electrical stimulation to different electrode combinations. Alternatively, in some embodiments, stimulation generator 30 may include multiple current or voltage sources to control delivery of stimulation energy to selected combinations of electrodes carried by leads 316.

[0092] Electrode combinations and other parameters associated with different therapy programs may be represented by data stored in a memory location, e.g., in memory 326, of IMD 314. Processor 324 may access the memory location to determine the electrode combination for a particular program and control stimulation generator 330 to deliver electrical stimulation via the indicated electrode combination. Each program may specify a set of parameters for delivery of electrical stimulation therapy. As an example, a program may specify electrode combination, electrode polarities, current or voltage amplitude, pulse rate and pulse width. Additional parameters such as duty cycle, duration, and delivery schedule also may be specified by a therapy program.

[0093] Using an external programmer, such as programmer 320, a user may select individual programs for delivery on an individual basis, or combinations of programs for delivery on a simultaneous or interleaved basis. In addition, a user may adjust parameters associated with the programs. The programs may be stored in memory 326 of IMD 314. Alternatively, the programs may be stored in memory associated with external programmer 320. In either case, the programs may be selectable and adjustable to permit modification of therapy parameters.

[0094] In some examples, programmer 320 may be a patient programmer, which may allow patient 312 to select among programs programmed by a clinician and stored in a memory of IMD 314 or the patient programmer. Additionally or alternatively, a patient programmer may allow patient 312 to adjust therapy parameters within a range determined by a clinician and stored in memory of the patient programmer or IMD 314. In addition, a physician programmer may permit generation of new programs, which may be loaded into memory 326, and adjustment of parameters associated with existing programs.

[0095] Upon selection of a particular program or program group from memory 326, processor 24 may control stimulation generator 330 to deliver stimulation according to the programs in the groups, e.g., simultaneously or on a time- interleaved basis. A group may include a single program or multiple programs, each of which specifies an electrode combination. Again, the electrode

combination may specify particular electrodes in a single array or multiple arrays, e.g., on a single lead or among multiple leads.

[0096] IMD 314 may be responsive to adjustments of programming parameters and electrode configurations by a user via programmer 320. In particular, processor 324 may receive adjustments to program parameters from programmer 320 via telemetry circuit 328. Telemetry circuit 328 may support wireless telemetry with external programmer 320 or another device by radio frequency (RF) communication, proximal inductive interaction of IMD 314 with external programmer 320, or other techniques. Telemetry circuit 328 may send information to and receive information from external programmer 320 on a continuous basis, at periodic intervals, or upon request from the stimulator or programmer. To support RF communication, telemetry circuit 328 may include appropriate electronic components, such as amplifiers, filters, mixers, encoders, decoders, modulators, demodulators and the like. In some examples, processor 324 also may

communicate information to programmer 320 or another external device via telemetry circuit 328.

[0097] Power source 332 delivers operating power to the components of IMD 314. Power source 332 may include a small rechargeable or non-rechargeable battery and a power generation circuit to produce the operating power. Recharging may be accomplished through proximal inductive interaction between an external charger and an inductive charging coil within IMD 314. In some examples, power requirements may be small enough to allow IMD 314 to utilize patient motion and implement a kinetic energy-scavenging device to trickle charge a rechargeable battery. In other embodiments, traditional non-rechargeable batteries may be used for a limited period of time. As a further alternative, an external inductive power supply could transcutaneous ly power IMD 314 when needed or desired.

[0098] Dynamic power adjustment circuitry 334 represents the various circuits described above which dynamically adjust the power supply voltage from power source 332 such that the power supply voltage is slightly greater than a power supply voltage required by output circuitry. Dynamic power adjustment circuitry 334 detects a first voltage at an output of stimulation generator 330, compares the detected first voltage and a second voltage, and adjusts a supply voltage from power supply 332 based on the comparison.

Claims

CLAIMS:

1. A method comprising:

detecting a first voltage at an output of a stimulation generator of a medical device;

comparing the detected first voltage and a second voltage; and

adjusting a supply voltage of the stimulation generator based on the comparison.

2. The method of claim 1, wherein detecting a first voltage comprises detecting a peak output voltage at the output of the stimulation generator, wherein the second voltage is the supply voltage, and wherein adjusting a supply voltage comprises controlling a voltage converter.

3. The method of claim 2, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a positive output voltage.

4. The method of claim 2, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a negative output voltage.

5. The method of claim 2, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a negative output voltage.

6. The method of claim 2, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a positive output voltage.

7. The method of claim 6, wherein the supply voltage is a first supply voltage, and wherein the voltage converter is a first voltage converter, the method further comprising:

detecting a negative peak output voltage;

comparing the detected negative peak output voltage and a second supply voltage; and

adjusting the second supply voltage from a second voltage converter based on the comparison.

8. The method of claim 7, wherein the second supply voltage is a negative output voltage.

9. The method of claim 1, wherein detecting a first voltage at an output of a stimulation generator of a medical device comprises detecting a voltage across a sense resistor coupled to the output, wherein comparing the detected first voltage and a second voltage comprises comparing the voltage detected across the sense resistor to a reference voltage, and wherein adjusting a supply voltage based on the comparison comprises adjusting a voltage from a voltage converter based on the voltage detected across the sense resistor.

10. The method of claim 9, wherein adjusting a voltage from a voltage converter based on the voltage detected across the sense resistor comprises:

turning off the voltage converter if an output current exceeds a value determined by dividing the detected voltage across the sense resistor and the resistance of the sense resistor.

11. A device comprising:

a detector configured to detect a first voltage at an output of a stimulation generator of a medical device;

a comparator configured to compare the detected first voltage and a second voltage; and

a voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison.

12. The device of claim 11, wherein the detector is configured to detect a first voltage is further configured to detect a peak output voltage at the output of the stimulation generator, wherein the second voltage is the supply voltage, and wherein the voltage converter configured to adjust a supply voltage is configured to control a voltage converter.

13. The device of claim 12, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a positive output voltage.

14. The device of claim 12, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a negative output voltage.

15. The device of claim 12, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a negative output voltage.

16. The device of claim 12, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a positive output voltage.

17. The device of claim 16, wherein the detector is a first detector, wherein the comparator is a first comparator, wherein the supply voltage is a first supply voltage of the stimulation generator, and wherein the voltage converter is a first voltage converter, the device further comprising:

a second detector configured to detect a negative peak output voltage; a second comparator configured to compare the detected negative peak output voltage and a second supply voltage of the stimulation generator; and

a second voltage converter configured to adjust the second supply voltage of the stimulation generator based on the comparison.

18. The device of claim 17, wherein the second supply voltage is a negative output voltage.

19. The device of claim 11, wherein the detector configured to detect a first voltage at an output of a stimulation generator of a medical device comprises a sense resistor coupled to the output, wherein the comparator configured to compare the detected first voltage and a second voltage is configured to compare the voltage detected across the sense resistor to a reference voltage, and wherein the voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison is configured to adjust a voltage from a voltage converter based on the voltage detected across the sense resistor.

20. The device of claim 19, wherein the voltage converter configured to adjust a voltage from a voltage converter based on the voltage detected across the sense resistor is further configured to:

turn off the voltage converter if an output current exceeds a value determined by dividing the detected voltage across the sense resistor and the resistance of the sense resistor.

21. The device of claim 11 , further comprising leads configured to be coupled to the stimulation generator, wherein the medical device is configured to be attached externally to a patient, wherein the leads are configured for implantation in the patient, and wherein the leads are configured to extend from the medical device through the skin of the patient to an implantation site in the patient.

22. An implantable medical device comprising an electronic circuit, the electronic circuit comprising:

a detector configured to detect a first voltage at an output of a stimulation generator of a medical device;

a comparator configured to compare the detected first voltage and a second voltage; and

a voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison.

23. The implantable medical device of claim 22, wherein the detector configured to detect a first voltage is further configured to detect a peak output voltage at the output of the stimulation generator, wherein the second voltage is the supply voltage, and wherein the voltage converter configured to adjust a supply voltage is configured to control a voltage converter.

24. The implantable medical device of claim 23, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a positive output voltage.

25. The implantable medical device of claim 23, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a negative output voltage.

26. The implantable medical device of claim 23, wherein the peak output voltage is a negative peak output voltage, and wherein the supply voltage is a negative output voltage.

27. The implantable medical device of claim 23, wherein the peak output voltage is a positive peak output voltage, and wherein the supply voltage is a positive output voltage.

28. The implantable medical device of claim 27, wherein the detector is a first detector, wherein the comparator is a first comparator, wherein the supply voltage is a first supply voltage of the stimulation generator, and wherein the voltage converter is a first voltage converter, the device further comprising:

a second detector configured to detect a negative peak output voltage; a second comparator configured to compare the detected negative peak output voltage and a second supply voltage of the stimulation generator; and a second voltage converter configured to adjust the second supply voltage of the stimulation generator based on the comparison.

29. The implantable medical device of claim 28, wherein the second supply voltage is a negative output voltage.

30. The implantable medical device of claim 22, wherein the detector configured to detect a first voltage at an output of a stimulation generator of a medical device comprises a sense resistor coupled to the output, wherein the comparator configured to compare the detected first voltage and a second voltage is configured to compare the voltage detected across the sense resistor to a reference voltage, and wherein the voltage converter configured to adjust a supply voltage of the stimulation generator based on the comparison is configured to adjust a voltage from a voltage converter based on the voltage detected across the sense resistor.

31. The implantable medical device of claim 30, wherein the voltage converter configured to adjust a voltage from a voltage converter based on the voltage detected across the sense resistor is further configured to:

turn off the voltage converter if an output current exceeds a value determined by dividing the detected voltage across the sense resistor and the resistance of the sense resistor

32. An electronic circuit comprising:

means for detecting a first voltage at an output of a stimulation generator of a medical device;

means for comparing the detected first voltage and a second voltage; and means for adjusting a supply voltage of the stimulation generator based on the comparison.