High-voltage DC/DC converter for high-efficiency power recovery in implantable devices

Abstract

Implantable biomedical devices such as sensors and neurostimulators require a near-field inductive link to transmit power wirelessly. However, the near-field induced voltage is usually much larger than the compliance of low-voltage integrated circuit technologies. Thus most integrated power recovery approaches limit the induced signal to low-voltages with inefficient shunt regulation, or voltage clipping. We propose using a high-voltage (HV) CMOS technology to fully integrate the inductive power recovery front-end while adopting a step-down approach where the induced signal is limited to a much higher voltage (20 V). We previously reported a first IC that includes a HV rectifier and a HV regulator, which provide up to 12 V regulated DC supply from a 20 V maximum AC input. In this paper, we report the design of a second HV custom IC that completes the front-end by integrating an adjustable step-down switched capacitor DC/DC converter (1:3, 1:2 or 2:3 ratio). The IC has been submitted for fabrication in DALSA-C08E technology and the total silicon area including pads is 9mm2. Post-layout simulation results show that the DC/DC converter achieves more than 90 % power efficiency while providing about 3.9 V output with 12 V input, 1 mA load, 1:3 conversion ratio, and 50 kHz switching frequency.