An Intra-Body-Power-Transfer System with a PLL-based Continuous Maximum Resonant Power Tracking Loop at TX and 1.8V DC Output Voltage at RX

Abstract

For miniaturization of wearable devices, battery-life extension and even battery-free operation are increasingly demanded. Intra-body-power-transfer (IBPT) has emerged as an alternative solution to energy harvesting [1] and wireless power transfer [2] because it can supply power regardless of the locations of the power source and the wearables on the body [3] -[5]. However, the channel characteristics of the body are prone to vary with environmental changes, making it hard to transfer sufficient power consistently [3]. To address this issue, a system with frequency and power adaptation for node-specific power delivery optimization was proposed [4]. However, it requires RX-to-TX backward data communication, disrupting the power transfer during the communication. Alternatively, a maximum-resonant-power-tracking (MRPT) was proposed. It adaptively changes the carrier frequency (fcarrier) so that the TX output voltage (VTX) is maximized [5]. However, its tuning phase, which is required for every MRPT operation period repeatedly, makes the IBPT discontinuous and inefficient.