A low-power silicon-on-insulator PWM discriminator for biomedical applications

A CMOS/SOI circuit to decode PWM signals is presented as part of a body-implanted neurostimulator for visual prosthesis. Since encoded data is the sole input to the circuit, the decoding technique is based on a double-integration concept and does not require DC filtering. Non-overlapping control phases are internally derived from the incoming pulses and a fast-settling comparator ensures good discrimination accuracy in the megahertz range. The circuit was integrated on a 2 μm single-metal SOI fabrication process and has an effective area of 2mm ². Typically, the measured resolution of the encoding parameter α was better than 10% at 6 MHz and V_DD=3.3 V. Stand-by consumption is around 340 μW. Pulses with frequencies up to 15 MHz and α=10% can be discriminated for V_DD spanning from 2.3 V to 3.3 V. Such an excellent immunity to V_DD deviations meets a design specification with respect to inherent coupling losses on transmitting data and power by means of a transcutaneous link