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HIGH-SPEED LOW-POWER VOLTAGE COMPARATOR TO FACILITATE AUTOMATIC COMPLIANCE VOLTAGE CONTROL FOR A NEUROSTIMULATOR

IP.com Disclosure Number: IPCOM000016848D
Publication Date: 2003-Jul-18

Publishing Venue

The IP.com Prior Art Database

Abstract

A high-speed, low-power voltage comparator circuit facilitates automatic compliance voltage control of an implantable neurostimulator device. The circuit detects if the drain voltage of an NMOS current sink falls below the voltage of 1.2 V, which is chosen because it is typically generated by a bandgap reference circuit and is therefore readily available, and because it is sufficiently greater than the typical voltage needed across the NMOS transistor to provide enough design margin so that the NMOS transistor functions as an ideal constant current sink. The circuit provided by the invention is low-power and therefore suitable for use in implantable biomedical applications because it consumes no quiescent current other than leakage currents of the circuit components. It is high-speed because the current needed to make the comparison decision can be set as high as needed to quickly drive parasitic load capacitances internal to the circuit.

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HIGH-SPEED LOW-POWER VOLTAGE COMPARATOR TO FACILITATE AUTOMATIC COMPLIANCE VOLTAGE CONTROL FOR A NEUROSTIMULATOR

Background

The present invention provides an automatic method of determining the minimum compliance voltage VH needed for any stimulation therapy in a neurostimulator device in which, during any stimulation pulse with one or more electrodes programmed to be a current sink, the voltage drop across each transistor acting as a current sink needs to be such that it sinks a constant current.� The comparator circuit provided by the invention offers a means for selecting which current sink transistor to monitor and for detecting when the drain-to-source voltage of the selected transistor falls below some minimum value below which the transistor fails to behave like an ideal current sink.

More particularly, the invention provides a circuit and method for detecting if the drain voltage of an NMOS current sink falls below the voltage of 1.2 V, which is chosen because it is typically generated by a bandgap reference circuit and is therefore readily available, and because it is sufficiently greater than the typical voltage, )V, needed across the NMOS transistor to provide enough design margin so that the NMOS transistor functions as an ideal constant current sink.� In general, any value greater than the designed )V with additional margin can be used as a voltage against which to compare the drain voltage of the current sink transistor.

The circuit provided by the invention is low-power and therefore suitable for use in implantable biomedical applications because it consumes no quiescent current other than leakage currents of the integrated circuit components.� It is high-speed because the current needed to make the comparison decision can be set as high as needed to quickly drive parasitic load capacitances internal to the circuit.

Detailed Description

As indicated previously, the present invention is directed to a high-speed low-power comparator circuit that may be used within a neurostimulator device.� More particularly, the invention provides an automatic way of determining the minimum compliance voltage VH needed for any stimulation therapy in a neurostimulator device in which, during any stimulation pulse with one or more electrodes programmed to be a current sink, the voltage drop across each transistor acting as a current sink needs to be such that it sinks a constant current.� The comparator circuit provided by the invention offers a means for selecting which current sink transistor to monitor and for detecting when the drain-to-source voltage of the selected transistor falls below some minimum value below which the transistor fails to behave like an ideal current sink.� While the invention is described with reference to a spinal cord stimulator (SCS), but it is understood that the invention may be used with any neural stimulator or similar circuit.

Turning first to FIG. 1, there is shown a spinal cord stimulator (SCS) output circuit c...