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 (RL) and coupling distance (d23) 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 RL by opening the switch. By adjusting the duty cycle (D), the loaded-Q of the Rx LC-tank can be dynamically modulated to compensate for variations in RL. 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 d23 = 8 cm, respectively, by compensating for 150 Ω variation in RL at D = 45%.

An Overview of Regulation Topologies in Resonant Wireless Power Transfer Systems for Consumer Electronics or Bio-Implants

“…To achieve a high VCE, a switching-based current-mode (SCM) regulating technique was proposed in [28][29][30][31]. This technique differs from voltage-mode ones by firstly storing the received energy in the RX LC resonant tank (as the resonant phase) and then delivering it to the load (charging phase).…”

“…A SCM RX based on Q-modulation was proposed in [28] as in Figure 15a, where the regulation is realized by modulating Q load . As in Figure 15b, the resonant phase (with T Φ1 duration) is activated by turning on the single switch S 1 .…”

“…The measured results showed that the V R can be boosted to 5.5 V. Figure 16. The switching waveforms of (a) Q-modulation [28] and (b) multi-cycle Q-modulation (MCQ) [30]. Ctrl is on-off control signal of the switch S 1 .…”

“…In addition, this synchronization makes it difficult for the system to work at a high resonant frequency, e.g., the 2 MHz resonant frequency in [28]. The measured result showed that the PTE was 40.5% at R L = 200 Ω with an 8-cm coil distance, and greater than 20% PTE can be achieved when R L ranges from 50 to 1000 Ω.…”

“…Therefore, the regulation schemes investigated in the previous works can also be categorized into two types: RX and TX regulation. As illustrated in Figure 3, RX regulation includes post-stage regulation (achieved by a cascading low dropout regulator (LDO [12][13][14][15] or a DC-DC converter [16][17][18][19][20]) and one-stage regulation, including active diode conduction time control [21][22][23], reconfigurable regulating rectification [24][25][26][27], and switching-based current-mode regulation [28][29][30][31]. On the other hand, TX regulation can be achieved by PA supply voltage control [32,33], resonant frequency control [34], PA power switch duty cycle control [35][36][37][38][39][40], and vector power summing control [41,42].…”