Power Management Using Photovoltaic Cells for Implantable Devices

This paper presents a novel inductor-less switched capacitor (SC) DC-DC converter, which generates simultaneous dual-output voltages for implantable electronic devices. Present dual output converters are limited to fixed ratio gain, which degrade conversion efficiency when the input voltage changes. The proposed power converter offers both step-up and step-down conversion with 4-phase reconfigurable logic. With an input voltage of 1 V provided by photovoltaic (PV) cells, the proposed converter achieves step-up, step-down, and synchronised voltage conversions in four gain modes. These are 1.5 and 0.5 V for normal mode, 2 and 1 V for high mode, 2 V for double boost mode, as well as 3 and 2 V for super boost mode with the ripple variation of 14-59 mV. The converter circuit has been simulated in standard 0.18-mu m CMOS technology and the results agree with the state-of-the-art SC converters. However, our proposed monolithically integrated PV powered circuit achieves a conversion efficiency of 85.26% and provides an extra flexibility in terms of gain, which is advantageous for future implantable applications that have a range of inputs. This research is, therefore, an important step in achieving truly autonomous implantable electronic devices.