This article analyzes the recently emerged resonant current-mode (RCM) topology and compares it with conventional voltage-mode (VM) rectifiers. Building upon prior RCM designs, a three-phase RCM rectifier is proposed to achieve a wider output power range and higher power efficiency, enabled by residual-free charge delivery through a bypass-capacitor-based mechanism. By incorporating a low-power freewheeling phase, the rectifier supports in situ output voltage regulation and inherently enables load-shift-keying (LSK)-based uplink data transfer, eliminating the need for additional voltage regulators or data links. A digitally assisted adaptive zero-voltage switching (ZVS) technique with fast delay compensation is implemented to minimize conduction losses in the power stage. Fabricated in a 180-nm CMOS process, the prototype occupies a silicon area of 0.4 mm². Measurement results demonstrate reliable hysteresis output regulation at 3.3V, while the output voltage can span a wide range from 2.2 to 4.4 V. The output power ranges from 0.4 to 209.4 mW. A peak power conversion efficiency (PCE) of 94.5% is achieved at 90.8-mW output power. The PCE remains above 80% for all tested output voltages (2.2, 3.3, 4.4 V) when the load current exceeds 1mA.

This thesis presents the design of integrated interface circuits for inductive resonant wireless power transfer (WPT) systems, targeting implantable medical devices (IMDs). IMDs require compact, high-efficiency, and robust wireless power solutions capable of adapting to link and load variations. This thesis systematically develops three receiver and system architectures: voltage-mode (VM), hybrid voltage-/current-mode (V/CM), and resonant-current-mode (RCM), to improve power conversion efficiency (PCE), voltage conversion ratio (VCR), and adaptability over state-of-the-art designs.

A bipolar quad-output regulating rectifier for wireless power transfer (WPT) is presented. Using only five power switches, it provides four independently regulated bipolar outputs. A coil-reused DC-DC mode sustains operation under heavy-load conditions beyond the RX input power limit. The rectifier achieves up to 173mW output power, 91% peak efficiency, and fast transient recovery.

A single-link wireless power and full-duplex data transfer system is presented. Operating at 40.68MHz, it delivers >50mW maximum output power with 61.1% peak end-to-end efficiency while supporting 17Mb/s uplink using resonance-length keying (RLK) and 3.4Mb/s downlink using instant-carrier-suspension keying (Instant-CSK). The design removes ASK/LSK trade-offs and achieves an aggregate data rate of half the carrier frequency using 180nm TX/RX chips and 15-/8-mm-diameter coils.

Vibration energy harvesting is a promising power solution for autonomous wireless sensor nodes, particularly in volume-constrained Internet-of-Things (IoT) applications. Piezoelectric (PE) and electromagnetic (EM) transducers are widely used to convert vibration energy into electrical power. While hybrid PE–EM harvesters can deliver higher output power to support self-sustained systems, existing implementations invariably rely on at least one off-chip inductor for either PE bias-flip or dc–dc conversion, substantially increasing system volume. This article presents an inductor-less, capacitor-less PE–EM hybrid energy harvesting platform that eliminates this limitation. By leveraging the inherent phase synchronization between PE and EM sources, the proposed coil-sharing technique enables both bias-flip and dc–dc conversion without additional passive components, enabling the first fully integrated hybrid energy harvesting system. Fabricated in 0.18- $\mu $ m CMOS technology, the prototype delivers dual-regulated outputs at 1.8 and 5 V for multi-domain sensor nodes, achieving a maximum output power of 2.72 mW and a peak end-to-end (E2E) efficiency of 90%. These results highlight the platform’s potential for ultra-compact, high-performance energy harvesting in next-generation IoT applications.

This article presents a 6.78-MHz switching-mode wireless power transfer (WPT) receiver (RX) with single-stage dual-output regulation and improved adaptability to link variations for biomedical applications. Based on a modified voltage doubler topology, it optimally transitions between voltage mode (VM) and resonant current mode (RCM) to extend the WPT range without compromising efficiency or delivered power. Seamless mode transition is achieved with no dead zones or output undershoots, thanks to the proposed quasi-open-circuit mode detection leveraging existing operational states without power-carrier interferences. The essential advantages of switching mode are consolidated via transient modeling. To meet dual-voltage-domain supply requirement in bio-implants, the RX uses stacked dc nodes in the voltage doubler to generate two regulated outputs with only three power switches. Designed and fabricated in a 180-nm CMOS technology, the proposed RX regulates two dc outputs at 1.8 and 3.3 V, respectively, with unobservable load-transient over/undershoots and cross-regulations. Using a 3.3-V-supplied class-D transmitter (TX), a 13.5-mm-radius TX coil, and an 11.5-mm-radius RX coil, the RX achieves a maximum WPT range of 7.5 cm under both 50-kΩ load conditions, demonstrating a 42% extension compared with VM-only operation. Real-time mode transition is validated through coil separation distance transients between 3 and 5.5 cm. In addition, with adaptive delay compensation in both VM and RCM operations, the RX achieves a peak power conversion efficiency (PCE) of 92.3% at a maximum output power of 171 mW.

This article presents a single-link, dual-output wireless power transfer (WPT) system operating at 40.68 MHz for miniature, high-power biomedical implants. The elevated carrier frequency enables a millimeter-scale receiver (RX) coil while maintaining link efficiency and output power comparable to low-frequency WPT designs. End-to-end (E2E) efficiency is optimized through global power modulation using a dynamic off-time (DOT) algorithm in conjunction with a fully integrated load-shift-keying (LSK) uplink. At the RX, a single-stage dual-output resonant-current-mode (DORCM) rectifier with single-mode zero-crossing-based control achieves zero-voltage switching (ZVS) and robust adaptability over varying coupling conditions. At the transmitter (TX), an adaptive-ZVS (AZVS) class-D power amplifier (PA) minimizes switching losses and electromagnetic interference (EMI). Both the TX and RX chips are fabricated in a 180-nm BCD process. Measurement results demonstrate dual-output voltage regulation at 1.2 and 2 V under DOT control (DOT Ctrl), with smooth switching behaviors observed at both the TX and RX. The DORCM RX supports seamless cold-start-up operation and achieves a peak power conversion efficiency (PCE) of 90.3% at 90.4-mW output power. The peak E2E efficiency is 51.2% at a coupling factor of k  = 0.2. Enabling DOT modulation improves E2E efficiency by up to 18.2%, corresponding to a 2.2× reduction in TX input power. The system delivers up to 149.7-mW output power with a TX input voltage of 5 V.

This paper presents a 6.78-MHz wireless power transfer (WPT) system for implantable biomedical devices. The receiver (RX) features a compact single-stage triple-output rectifier that delivers three regulated DC outputs (1V, 2V, and 3 V) using only two power transistors and two buffer capacitors. A novel load-shift-keying (LSK) technique, hybridizing the shortcircuit (SC) LSK and resistive-circuit (RC) LSK, is proposed, achieving low-loss power-data backscattering and fully integrated global power regulation between the RX and transmitter (TX) chips. TX and RX chips were designed and fabricated in a 180-nm BCD process. Measurement results show that the system provides three regulated DC outputs at 1V, 2V, and 3V, respectively, with unnoticeable cross-regulations and load transients. Supplied by a 3.3-V input at TX, it achieves 200.2 mW peak output power, 66.1% peak end-to-end (E2E) power efficiency, and up to 27.3% E2E-efficiency enhancement thanks to global power regulation.

This paper presents a fully-integrated single-input dual-output power management unit operating both in volt age/current modes for powering mm-scale wireless neural im plants. The chip operates in voltage mode most of the time, using an active full-wave rectifier to regulate a low-voltage, high load output with high power efficiency and low output ripple (<32 mV_pp). It switches to current mode rectification when gen erating a high-voltage, low-load output. This dual-mode operation allows for flexible power distribution and configurable voltage ratios between the two outputs. The selected 40.68 MHz operating frequency reduces the required capacitances for input impedance matching and output filtering, enabling on-chip integration; the only external component is the receiver coil. A novel resonance breakup switch compatible with full-wave rectification ensures a smooth cold start-up of the chip without any external voltage supply. The chip was fabricated using 40-nm CMOS technology with an active area of 1.18 mm² and was tested in a wireless power link. Measurement results demonstrate that the chip can simultaneously regulate two outputs, V_LV = 1 V and V_HV = 2 V, with a tested maximum output power of 10 mW and 32.6 µW on V_LV and V_HV, respectively. At the optimal output power condition (P_LV = 4.4∼6.7 mW), the system achieves a peak power conversion efficiency of 85.87% and a peak end-to-end efficiency of 17.32% when regulating V_LV. The end-to-end efficiency drops by only 2.38% when regulating both outputs with R_LV = 225 Ω and R_HV = 400 kΩ.

This article presents a 13.56-MHz wireless power transfer (WPT) system with coupling variation robustness and high efficiency for powering biomedical implantable devices (IMDs). To sustain reliable power transfer against inductive-link fluctuation, a hybrid voltage-/current-mode (V/CM) receiver (RX) is proposed to provide CM recovery when the coupling becomes weak for VM operation. To optimize the end-to-end (E2E) efficiency, a digital pulsewidth modulation (PWM)-based global power regulation technique is proposed, which allows a fully on/off operation of the three-mode power amplifier (PA) at the transmitter (TX) side and fast load-transient responses. Moreover, the system adopts a fully integrated voltage-sensing load-shift-keying (LSK) demodulation technique, which replaces conventional current sensing methods with a streamlined implementation and reduced power consumption. Both prototype TX and RX chips were fabricated in a 180-nm CMOS process. The proposed system, powered by a 1.8-V supply at TX, realizes a regulated 1.8-V dc output at RX. With the help of the hybrid V/CM RX, the proposed system achieves an up-to-150% WPT range extension compared to VM-only operation and an up to 7.2-cm WPT range. Benefiting from the global digital-PWM regulation, it achieves up to 72.3% E2E efficiency over the loading range from 0.18 to 81 mW. A 10- μ s load-transient recovery is also attained at a 164 × load step with a 110-mV undershoot and unnoticeable overshoots.

A single-stage dual-output regulating voltage doubler (DOVD) is proposed for biomedical wireless power transfer (WPT) systems. Derived from the full-wave voltage doubler (VD) topology, it achieves ac-to-dc rectification and dual-output voltage regulation in a single stage by using only two power transistors. The DOVD's inherent voltage conversion ratio (VCR) of 2 enhances the overall voltage gain of a WPT system, thus extending the transfer range against varying link conditions. To eliminate cross-regulation between the two outputs and provide fast load-transient responses, a parallel pulse-frequency modulation (PPFM) controller is proposed. In addition, a digital-tuning adaptive delay compensation technique with fast error-variation responses is proposed to achieve soft-switching in the power stage. Implemented in a 180-nm Bipolar-CMOS-DMOS (BCD) technology and operating at 6.78 MHz, the proposed DOVD achieves dual regulated outputs at 1.8 and 3.3 V, a VCR of up to 1.875, and a power conversion efficiency (PCE) of up to 92.95% over an output power range of 2.6-90.5 mW. It also achieves instant load-transient responses and unnoticeable cross-regulation during 25× load transients at both outputs.

This work presents a switched capacitor power converter (SCPC) with instant transient response and minimized steady-state output ripple. The proposed SCPC employs a hybrid control strategy that amalgamates the strengths of hysteresis and continuous frequency modulation (CFM) controls, thus elevating transient performance while maintaining a small steady-state ripple. The system adopts a 10 -phase interleaved recursive switched capacitor (RSC) topology with adaptive capacitor sizing to achieve configurable voltage-conversion ratios (VCR) with heightened efficiency, power density, and load ability. Additionally, a novel adaptive switch-sizing technique is introduced to improve light-load efficiency. Fabricated in 180-nm BCD technology, the chip supports a wide-range load current of 0.7mA-120mA and converts a 0.8 -to-3.6V input to a 0.25 -to2.4 V output with a peak efficiency of 87.1%. The proposed converter simultaneously achieves a low voltage ripple of 12 mV and an over-/under-shoot voltage of less than 50 mV even under significant load transient steps (171X).

This paper presents a Switching-Mode Regulating Rectifier (SM-RR) with single-stage dual-output regulation for biomedical wireless power transfer applications. To achieve both a high power conversion efficiency (PCE) and a long power transfer distance, the proposed SM-RR can seamlessly switch its operation between voltage mode and resonant current mode. To meet multi-power-rail requirements in loading circuits, it employs only three power transistors to provide two regulated outputs with parallel pulse-frequency modulation, which achieves unobservable cross-regulations. The prototype chip, fabricated in a 180 nm CMOS process, achieves two regulated outputs at 1.8 V and 3.3 V, respectively, up-to- 92.33% PCE, and up-to-42% transfer range extension compared to conventional voltage-mode receivers.

This article presents a 10mV-startup-voltage thermoelectric energy harvesting system, assisted by a piezoelectric generator (PEG) as a cold starter. It exploits the fact that when a thermoelectric energy harvesting system is implemented in a place where kinetic energy is also present, the PEG starter can provide a clock signal to start the system. Thanks to the high output impedance of the PEG, the generated clock voltage can easily go over several hundreds of mV, which can be used to drive the boost converter to harvest thermoelectric energy even at an extremely low thermoelectric generator (TEG) voltage. The proposed system was fabricated in a 180-nm BCD process. The measurement results show that the TEG system can start up from the cold state with a TEG voltage as low as 10 mV while maintaining a 63.9% efficiency. The peak power conversion efficiency reaches 83.7% when the TEG voltage is 55 mV.

In this article, we propose a reconfigurable regulating rectifier with a wide operational range for wireless power transfer. The proposed three-mode rectifier achieves a broad range voltage regulation without global loop control to minimize the chip area occupation. Compared with previous work, more working modes and greater voltage gain allow the proposed rectifier to regulate lower input power, which extends the voltage regulation range. A local loop control scheme is proposed for voltage rectification with three modes. It adaptively senses the duty cycle of the mode signal to determine the working mode of the rectifier, and configure the rectifier to the desired mode for voltage regulation. The proposed system was designed and fabricated in a 180-nm BCD technology with an active area of 1.17 mm2. The measurement results show that the proposed system can rectify wide-range input ac power to a regulated output. The achieved voltage conversion ratiois between 0.95X and 2.68X, with a peak power conversion efficiencyat 87.4%.

In this letter, a 6.78-MHz single-stage regulating voltage-doubling rectifier is presented for biomedical wireless power transfer (WPT) applications. Derived from a full-wave voltage doubler, a theoretical voltage conversion ratio (VCR) of 2 can be achieved, which benefits the end-to-end voltage gain of a biomedical WPT system with varying link conditions. As a result, a wider WPT operational range and less coil-link loss can be achieved. To avoid efficiency loss due to cascading, the rectifier output is in-situ regulated in a sub-50-mV hysteresis window by pulse-skipping control. To ensure a high power conversion efficiency (PCE), adaptive delay-compensated active diodes are adopted with an offset locking technique. The input/output capacitors of the rectifier are fabricated on-chip, achieving a fully integrated design. The rectifier was fabricated in a 180-nm BCD process, occupying a silicon area of 0.3/2.7 mm2 without/with on-chip capacitors. The measurements show that the rectifier can realize a peak PCE at 90.6% when the output power is 79.8 mW. The PCE and VCR are achieved higher than 86.4% and 1.6, respectively, over a large loading range (from 1 to 40 mA). The rectifier can output a maximum power of 159.2 mW, satisfying most biomedical implants.

Dual-output regulating rectifier is highly desired in wireless power transfer (WPT) for sub-100mW bioimplants. Such rectifiers perform voltage rectification and dual-output regulation simultaneously, thus avoiding post DC-DC conversions and cascaded power losses [1 –4]. However, the conventional dual-output structure suffers from a low voltage conversion ratio (VCR) (< 1) due to the full bridge rectifier (FBR) topology (Fig. 1), severely limiting the receiver operation when wireless link condition varies [1–2]. In order to extend the operational range without increasing the power demand from the transmitter, [3] presents a charge-pump based dual-output rectifier; however, it uses 10 power transistors (PTs) and 8 off-chip capacitors, degrading the power conversion efficiency (PCE) and increasing the integration cost. Alternatively, the current-mode dual-output rectifier can realize a VCR higher than 1, but the output power is limited to less than 10mW [4], which is insufficient for advanced bioimplants. In this work, a 13. 56MHz single-stage dual-output voltage doubler (DOVD) is proposed to address the above limitations, which employs only two PTs and a fully integrated design. lt can achieve a peak VCR of1.78 and outputs power up to 8lmWwith a 91.8% peak PCE.

A 6.78 MHz dual-output reconfigurable rectifier for wireless power transfer is presented. The proposed rectifier integrates AC-DC rectification and DC-DC regulation into a single-stage topology, alleviating received power loss and reducing system volume cost. By adding a switch matrix after rectifying bridge, a dual output can be realized and regulated by a hysteretic control unit. The proposed rectifier can work in six operation modes by reconfiguring, and each output can be regulated in three modes. As a result, fine output regulation and large output-driving capability can be achieved. Designed in a 180-nm BCD process using standard 5-V devices, the dual-output rectifier provides two output voltages at 3 V and 5 V, and delivers a maximum power of 1.6 W. The peak post-layout simulated power conversion efficiency reaches 80.1% when both load currents are 0.2 A.