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 bodyimplanted 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 fastsettling comparator ensures good discrimination accuracy in the megahertz range. The circuit was integrated on a 2mm single-metal thin-film CMOS/SOI fabrication process and has an effective area of 2 mm. Measured resolution of encoding parameter a is better than 10% at 6 MHz and VDD 1⁄4 3:3 V: Idle-mode consumption is 340mW. Pulses of frequencies up to 15 MHz and a 1⁄4 10% can be discriminated for 2:3 V # VDD # 3:3 V: Such an excellent immunity to VDD deviations meets a design specification with respect to inherent coupling losses on transmitting data and power by means of a transcutaneous link.