A Q-Modulation Technique for Efficient Inductive Power Transmission

Abstract

A fully-integrated power management ASIC for efficient inductive power transmission has been presented capable of automatic load transformation using a method, called Q-modulation. Q-modulation is an adaptive scheme that offers load matching against a wide range of loading (<i>R_L</i> ) and coupling distance (<i>d₂₃</i> ) variations in inductive links to maintain high power transfer efficiency (PTE). It is suitable for inductive powering implantable microelectronic devices (IMDs), recharging mobile electronics, and electric vehicles. In Q-modulation, the zero-crossings of the induced current in the receiver (Rx) LC-tank are detected and a low-loss switch chops the Rx LC-tank for part of the power carrier cycle to form a high-Q LC-tank and store the maximum energy, which is then transferred to <i>R_L</i> by opening the switch. By adjusting the duty cycle (<i>D</i>), the loaded-Q of the Rx LC-tank can be dynamically modulated to compensate for variations in <i>R_L</i> . A Q-modulation power management (QMPM) prototype chip was fabricated in a 0.35-μm standard CMOS process, occupying 4.8 mm². In a 1.45 W wireless power transfer setup, using a class-E power amplifier (PA) operating at 2 MHz, the QMPM successfully increased the inductive link PTE and the overall power efficiency by 98.5% and 120.7% at <i>d₂₃</i> = 8 cm, respectively, by compensating for 150 Ω variation in <i>R_L</i> at <i>D</i> = 45%.