A 13.56 MHz time-interleaved resonant-voltage-mode wireless-power receiver with isolated resonator and quasi-resonant boost converter for implantable systems

Abstract

Wireless power transfer (WPT) has been widely adopted in various applications, such as biomedical implants and wireless sensors. A conventional voltage-mode receiver (VM-RX) uses a rectifier or a doubler for AC-DC conversion [1,2]. This requires a sufficiently large input power (P,N) inducing a large voltage (VAC) in the LC tank of the receiver (RX) due to the limited voltage conversion efficiency. A subordinate DC-DC converter is also required for voltage regulation or battery charging, which reduces the overall power-conversion efficiency (PCE) due to the 2-stage structure. To overcome these limitations, the resonant current-mode receiver (RCM-RX) has been proposed for direct battery charging [3] and voltage regulation [4,5]. The RCM-RX has two operation phases: a resonance phase (PHre) that accumulates energy in the LC tank during optimal resonant cycles (NOPT) to track the maximum efficiency [3], and a charging phase (PHch) that delivers the energy of the LC tank to the output, when the resonant current (IAC) is at its peak. However, the RCM-RX typically operates at low resonant frequency fRESO (50kHz to 1MHz) because it is challenging to accurately detect the peak timing of IAC due to the intrinsic delay and offset of the comparator used in the peak timing detector. Operating at low fRESO causes the coil size to increase, making a burden on a size-constrained implant. In addition, the RCM-RX has a LC-tank resonance-loss interval PHch, which hinders optimal power transfer from the transmitter (TX) to the RX because the reactive impedance is not cancelled out but appears on the TX side. Because the LC tank and the output are not isolated during PHch, the power-transfer efficiency (PTE) can also be affected by load variation, such as the battery-voltage (VBAT) variation. These problems become worse as NOPT is reduced to lower number.