Low Power Loss Current Digital-to-Analog Converter Used in an Implantable Pulse Generator

• US 20090204174A1
• Filed: 04/16/2009
• Published: 08/13/2009
• Est. Priority Date: 05/28/2004
• Status: Active Grant

• Current Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Original Assignee: Boston Scientific Neuromodulation Corporation (Boston Scientific Corporation)
• Inventors: Nimmagadda, Kiran, He, Yuping, Parramon, Jordi
• Granted Patent: US 8,750,985 B2
• Time in Patent Office: Days
• US Class Current: 607/46
• CPC Class Codes: A61N 1/025 Digital circuitry features of electrotherapy devices, e.g. memory, clocks, processors
• CPC Class Codes: A61N 1/36071 Pain
• CPC Class Codes: A61N 1/36125 Details of circuitry or electric components
• CPC Class Codes: A61N 1/378 Electrical supply

Abstract

In one embodiment, the present invention provides an implantable stimulation device that includes output current sources and/or sinks configured to provide an output current for a load (i.e., tissue). The output path of the output current source or sink comprises a transistor which operates in a linear mode instead of a saturation mode. Because operation in a linear mode results in smaller drain-to-source voltage drops, power consumption in the output current source or sink (and hence in the implantable stimulator) is reduced, reducing battery or other power source requirements. Operation in the linear mode is facilitated in useful embodiments by a load in an input path (into which a reference current is sent) and a load in the output path (which bears the output current). The loads can be active transistors or passive resistors. A feedback circuit (e.g., an operational amplifier) receives voltages that build up across these loads, and sends a control signal to the gate of the transistor to ensure its linear operation.

Claims

1. An implantable stimulator device, comprising:

a first load having a first end and a second end, the first end of the first load coupled to a first power supply and the second end of the first load coupled to a reference current;

a second load having a first end and a second end, the first end of the second load coupled to the first power supply; and

a first transistor having a drain, a source and a gate, wherein the source is coupled to the second end of the second load, and the drain is coupled to a first electrode implantable adjacent to tissue to be stimulated,

wherein the first transistor provides an output current to the first electrode and is controlled at its gate to operate in a linear mode.

2. The device of claim 1, wherein the output current equals the reference current.

3. The device of claim 1, wherein the output current is N times higher than the reference current.

4. The device of claim 1, wherein the ratio between the reference current and the output current is set by the ratio between impedances of the first and second loads.

5. The device of claim 1, wherein the first and second loads comprise resistors.

6. The device of claim 1, wherein the first and second loads comprise transistors.

7. The device of claim 6, wherein the first and second load transistors comprise matched active loads.

8. The device of claim 1, wherein a magnitude of the output current is programmable.

9. The device of claim 1, wherein the magnitude of the output current is programmable by adjusting an impedance of the second load.

10. The device of claim 1, further comprising:

a third load having a first end and a second end, the first end of the third load coupled to a second power supply and the second end of the third load coupled to a reference current;

a fourth load having a first end and a second end, the first end of the fourth load coupled to the second power supply; and

a second transistor having a drain, a source and a gate, wherein the source is coupled to the second end of the fourth load, and the drain is coupled to a second electrode implantable adjacent to tissue to be stimulated,

wherein the second transistor provides an output current to the second electrode and is controlled at its gate to operate in a linear mode.

11. An implantable stimulator device, comprising:

a first load having a first end and a second end, the first end of the first load coupled to a first power supply and the second end of the first load coupled to a reference current;

a second load having a first end and a second end, the first end of the second load coupled to the first power supply;

a first transistor for providing an output current to a first electrode implantable adjacent to tissue to be stimulated, the first transistor coupled between the second end of the second load and the first electrode, the second load and first transistor comprising an output path for the output current; and

a first feedback circuit for controlling the first transistor in accordance with at least a first voltage taken on the output path.

12. The device of claim 11, wherein the feedback circuit operates the first transistor in a linear mode.

13. The device of claim 11, wherein the first voltage comprises a voltage at the second end of the second load.

14. The device of claim 11, wherein the feedback circuit further controls the first transistor in accordance with a second voltage comprising a voltage at the second end of the first load.

15. The device of claim 14, wherein the feedback circuit compares the voltages at the second ends of the first and second loads and produces a digital output of the comparison.

16. The device of claim 11, wherein the feedback circuit comprises an operational amplifier.

17. The device of claim 11, wherein an output of the feedback circuit is connected to a gate of the first transistor.

18. The device of claim 11, wherein the output current is N times higher than the reference current.

19. The device of claim 11, wherein the ratio between the reference current and the output current is set by the ratio between impedances of the first and second loads.

20. The device of claim 11, wherein the first and second loads comprise resistors.

21. The device of claim 11, wherein the first and second loads comprise transistors.

22. The device of claim 11, wherein a magnitude of the output current is programmable.

23. The device of claim 11, further comprising:

a third load having a first end and a second end, the first end of the third load coupled to a second power supply and the second end of the first load coupled to a reference current;

a fourth load having a first end and a second end, the first end of the fourth load coupled to the second power supply;

a second transistor for providing an output current to a second electrode implantable adjacent to tissue to be stimulated, the second transistor coupled between the second end of the fourth load and the second electrode, the fourth load and second transistor comprising the output path for the output current; and

a second feedback circuit for controlling the second transistor in accordance with at least a first voltage taken on the output path.