Low-power, high-modulation-index amplifier for use in battery-powered device

• US 20020032471A1
• Filed: 08/31/2001
• Published: 03/14/2002
• Est. Priority Date: 09/06/2000
• Status: Active Grant

• Current Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Original Assignee: Advanced Bionics Corporation (Sonova Holding AG)
• Inventors: Loftin, Scott M., McClure, Kelly H.
• Granted Patent: US 6,591,139 B2
• Time in Patent Office: Days
• US Class Current: 607/61
• CPC Class Codes: A61N 1/37211 Means for communicating with stimulators
• CPC Class Codes: A61N 1/37276 characterised by means for reducing power consumption during telemetry
• CPC Class Codes: A61N 1/3787 from an external energy source
• CPC Class Codes: Y10S 128/902 Biological signal amplifier
• CPC Class Codes: Y10S 128/903 Radio telemetry

Abstract

An external transmitter circuit drives an implantable neural stimulator having an implanted coil from a primary coil driven by a power amplifier. For efficient power consumption, the transmitter output circuit (which includes the primary coil driven by the power amplifier inductively coupled with the implanted coil) operates as a tuned resonant circuit. When operating as a tuned resonant circuit, it is difficult to modulate the carrier signal with data having sharp rise and fall times without using a high power modulation amplifier. Sharp rise and fall times are needed in order to ensure reliable data transmission. To overcome this difficulty, the present invention includes an output switch that selectively inserts a resistor in the transmitter output coil circuit in order to de-tune the resonant circuit only during those times when data modulation is needed. Such de-tuning allows sharp rise and fall times in the data modulation without the need for using a high power modulation amplifier. Because data modulation is typically needed for only a small percent of the time that a carrier signal is present, it is thus possible using the present invention to achieve reliable data modulation, transmission and reception without having to use a high power modulation amplifier in the transmitter.

Claims

1. A low power modulation amplifier circuit adapted to be coupled with an implantable device, comprising:

an amplifier having an output port through which a carrier signal is presented to a load, the load including an implantable coil associated with the implantable device;

a first capacitance connected between the output port of the amplifier and a voltage reference;

an antenna coil connected to the output port of the amplifier, the antenna coil comprising part of the load to which the carrier signal is presented by the amplifier;

a resistor connected to the antenna coil; and

a switch that switchably connects the resistor in circuit relationship with the antenna coil.

2. The amplifier circuit of claim 1 wherein the resistor is connected in series with the primary coil when the switch is opened.

3. The amplifier circuit of claim 1 wherein the resistor is connected in parallel with the primary coil when the switch is closed.

4. The amplifier circuit of claim 1 wherein the antenna coil forms part of a resonant circuit;

and wherein the switch, when connected to the antenna coil, de-tunes the resonant circuit so that the resonant circuit has a Q of four or less.

5. The amplifier circuit of claim 4 wherein the carrier signal is modulated at a low duty cycle of no greater than about 4 percent.

6. The amplifier circuit of claim 5 wherein the carrier signal is modulated at a low duty cycle of no greater than about 2 percent.

7. The amplifier circuit of claim 1 wherein the switch comprises a plurality of switches connected in parallel.

8. The amplifier circuit of claim 1 wherein the switch comprises a multiplicity of switches connected in parallel.

9. An implantable medical device system comprising

an external power amplifier, having a primary coil;

and

an implant device, having an implanted coil;

means within the power amplifier for generating a carrier signal that is inductively coupled from the primary coil to the implanted coil through a high Q resonant circuit that includes the primary coil and the implanted coil, and wherein the Q of the high Q resonant circuit is at least 10;

means within the power amplifier for modulating the carrier signal with data;

a resistor and a switch within the power amplifier, wherein the resistor is connected to the primary coil through the switch, and wherein the resistor, when connected to the primary coil, de-tunes the high Q resonant circuit; and

means within the power amplifier for operating the switch to de-tune the resonant circuit when the carrier signal is modulated with data, wherein the de-tuned resonant circuit allows the data modulation of the carrier signal to occur with sharper rise and fall times, which sharper rise and fall times, in turn, are more reliably detected as data within the implant device.

10. The implantable medical device system of claim 9 wherein the resistor is connected in series with the primary coil when the switch is opened.

11. The implantable medical device system of claim 9 wherein the resistor is connected in parallel with the primary coil when the switch is closed.

12. The implantable medical device system of claim 9 wherein the switch, when connected to the coil, de-tunes the resonant circuit so that the Q of the resonant circuit is four or less.

13. The implantable medical device system of claim 9 wherein the carrier signal is modulated at a low duty cycle of no greater than about 4 percent.

14. The implantable medical device system of claim 9 wherein the carrier signal is modulated at a low duty cycle of no greater than about 2 percent.

16. The method of claim 15 wherein step (d) includes switchably connecting a resistor in circuit relationship with the primary coil in order to lower the Q of the resonant circuit that includes the primary coil and the implanted coil.

17. The method of claim 15 wherein the step of switchably connecting the resistor in circuit relationship with the primary coil comprises connecting the resistor in series with the primary coil.

18. The method of claim 15 wherein the step of switchably connecting the resistor in circuit relationship with the primary coil comprises connecting the resistor in parallel with the primary coil.

19. The method of claim 15 wherein the step of switchably connecting a resistor in circuit relationship with the primary coil comprises shunting the resistor with a closed switch, thereby effectively removing the resistor from the circuit relationship with the primary coil.

20. The method of claim 19 wherein shunting the resistor with a closed switch comprises shunting the resistor with a plurality of switches connected in parallel.

15. A method of reliably and efficiently transmitting data and power to an implantable medical device from an external power amplifier, wherein the implantable medical device includes an implanted coil, and the external power amplifier includes a primary coil;

the method comprising;

the steps of;

(a) generating a carrier signal in the power amplifier;

(b) inductively coupling the carrier signal from the primary coil to the implanted coil through a resonant circuit having a Q of at least 10 that includes the primary coil and the implanted coil when only power is to be transmitted to the implantable medical device;

(c) modulating the carrier signal with data when data is to be transmitted to the implantable medical device; and

(d) inductively coupling the modulated carrier signal from the primary coil to the implanted coil through a resonant circuit having a Q of less than about 4 that includes the primary coil and the implanted coil.