A CMOS/SOI Single-input PWM Discriminator for Low-voltage Body-implanted Applications

A CMOS/SOI circuit to decode Pulse-Width Modulation (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 novel double-integration concept and does not require low-pass 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 thin-film CMOS/SOI fabrication process and has an effective area of 2 mm². Measured resolution of encoding parameter α is better than 10% at 6 MHz and V_DD = 3.3 V. Idle-mode consumption is 340 μW. Pulses of frequencies up to15 MHz and α =10% can be discriminated for 2.3 V ≤ V_DD ≤ 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.