Control methodology for on-chip switching power supplies for biomedical implants

Recent developments in biomedical implants have increased the demand for on-chip power supplies. Switching power supplies provide high efficiency solution, which also serves in reducing the size of energy harvesting or energy storage devices. Hence, on-chip switching power supplies are ideal for implantable applications. However, they have the problem of higher ripple at the output than the conventional linear regulator due to the impractical values of on-chip components. In this paper, we present a new control methodology for on-chip switching power supply optimized for inductively powered implantable devices without any off-chip filtering components. The control methodology smoothens the transition between switching states based on pulse density modulation (PDM) feedback, in addition to an output voltage slope-limiting circuit. Simulated results of output ripple and efficiency based on 130nm RF-CMOS are shown. The control methodology reduce the ripple with minimal effect on power efficiency and without the need for any external filtering components.