M. Nieves Ruiz

A class E synchronous rectifier based on an E-pHEMT device for wireless powering applications

In this paper, the design of a class E synchronous rectifier, working in the 900 MHz frequency band and based on an Enhancement-mode Pseudomorphic High Electron Mobility Transistor (E-PHEMT), is proposed. Thanks to its small on-state resistance and its slightly positive threshold voltage, this type of device may offer an excellent performance when operated as a switch without biasing its gate terminal. After properly extracting its model parameters, the optimum drain terminations, required for guaranteeing zero-voltage and zero-derivative switching conditions (ZVS and ZDS), were estimated. Taking advantage of the time-reversal duality, a lumped-element class E amplifier was first designed, to then introduce a drain-to-gate feedback and operate it in the desired synchronous rectifying mode. An efficiency peak of 83% has been measured at 17 dBm, staying above 70% for a 14 dB input power range, a distinguishing characteristic when compared to Schottky diode based alternatives. The verified AM-AM conversion linearity would also allow using the rectifier for the efficient extraction of a time-varying excitation envelope without significant distortion.

A reconfigurable class E oscillator/rectifier based on an E-pHEMT

In this paper, a reconfigurable class E oscillator/rectifier, based on an Enhancement-mode Pseudomorphic High Electron Mobility Transistor (E-pHEMT), is proposed. Using high Q lumped elements for implementing the desired terminations at drain side, as well as for the feedback/phase shifting network, the same circuit can be used either as a DC-to-RF inverter for efficient signal transmission, or as a RF-to-DC rectifier for wireless powering. Designed at the 960 MHz frequency band, an efficiency value of 76% has been measured in the oscillating mode for an output power of 17.5 dBm, with a -127 dBc/Hz phase noise figure at 1 MHz frequency offset. A 79.6% peak efficiency value has been obtained when operated as rectifier.

A UHF class E 2 DC/DC converter using GaN HEMTs

In this paper, the design of a class E2 resonant DC/DC converter, operating at UHF band, is proposed. Combining the use of GaN HEMT devices, both for the inverter and the synchronous rectifier, with high Q lumped-element multi-harmonic matching networks, a peak efficiency value of 72% has been obtained at 780 MHz with a 10.3 W output power. By means of a Pulse Width Modulation (PWM) over the gate driving envelope, the output voltage may be controlled while keeping low switching losses, with an estimated small-signal bandwidth (BW) and a slew rate of 11 MHz and 630 V/µSeg, respectively.

Class-E power converters for AC (50/60 Hz) wireless transmission

In this paper, class-E power amplifiers (PAs) and rectifiers, operating at UHF band, are properly integrated in efficient AC-to-RF and RF-to-AC converters for their use in 50/60 Hz wireless power transmission (WPT). Slightly modifying a center-tap full-wave rectifier, it is proved that a 915 MHz frequency carrier may be high-level amplitude modulated by each of the semi-cycles of the utility waveform. Assuming those components are transmitted by means of orthogonal antenna polarizations, the high-fidelity recovery of both semi-sinusoids in the remote position is also demonstrated, to be stepped-up and combined at the Δ port of an additional center-tap transformer. GaN HEMT packaged devices were selected for the designed PAs, while Schottky diodes for the rectifiers, resulting in average efficiency figures of 83.3% and 75.4%, respectively.

Class-E amplifier and rectifier for a wireless link with secure signal and simultaneous power transmission

In this paper, the design and implementation of a GaN HEMT class-E power amplifier and a Schottky diode class-E rectifier are described. Based on the widely known Linear Amplification with Nonlinear Components technique (LINC), and taking advantage of the spatial power combining capability of a dual-fed square patch, the highly efficient amplifier and rectifier may be incorporated at both sides of a wireless link, proposed for the simultaneous transmission of signal and power to a remote receiver.

Efficient class-E power amplifier for variable load operation

In this paper, a GaN HEMT class-E power amplifier (PA) has been designed for efficiently operating under variable load resistance at the 750 MHz frequency band. The desired zero voltage switching (ZVS) of the device can be approximated for a wide range of resistive loads, by means of a simple inductive impedance inverter, derived from [1]. The load-pull contours, obtained from simulations, allowed the drain terminating network to be properly adjusted in order to maximize the output power control while at the same time minimizing losses. Once the amplifier was implemented, an efficiency over 76% has been measured at 9.6 dB power back-off, with a peak of 85% at 50 Ω. In addition, the efficiency stays as high as 75% for a 150 MHz frequency range.

GaN HEMT class-E rectifier for DC+AC power recovery

A 915 MHz GaN HEMT-based class-E rectifier is proposed in this paper to be used for DC+AC wireless power recovery. Taking advantage of the time reversal (TR) duality principle, the rectifier was derived from a class-E inverter, whose output network was designed for high-efficiency operation over a wide range of resistive loads. The addition of an appropriate gateside termination allows the device to be turned-on without an additional RF source for gate driving. The rectifier reduced sensitivity to load variation, as well as its capability for efficiently and linearly recovering the envelope of an AM RF excitation, were then characterized. An average efficiency of 82% has been measured for the combined RF-to-DC and RF-to-AC power conversion of a 1.6 W modulated carrier. Frequency multiplexing and frequency modulation alternatives for high-level DC+AC wireless power transmission are finally presented.

UHF power conversion with GaN HEMT class-E 2 topologies

This paper reviews the use of UHF double class-E (class-E2) topologies for dc/dc power conversion. After introducing this attractive resonant converter in the context of the time-reversal duality principle, two different lumped-element networks are described for appropriately terminating the drain of the switching devices. Recent implementation examples, taking advantage of GaN HEMT processes, are then presented. The potential for a fast dynamic response is validated (with a slew rate over 2 V/nS), while also the feasibility for an appropriate operation without requiring external RF gate driving signals. A solution for approximating a load-insensitive operation is finally exposed.

Constant-gain envelope tracking in a UHF outphasing transmitter based on continuous-mode class-E GaN HEMT PAs

A UHF outphasing transmitter, based on continuous-mode class-E power amplifiers (PAs) and implementing a constant-gain envelope tracking (ET) strategy, is presented in this paper. Drain terminating and biasing networks are designed to provide near optima impedance values at the fundamental and higher order harmonics to the selected GaN HEMT device. A high-efficiency wideband performance, 80% for a 630-890 MHz range, is obtained, besides being amenable for load-modulation through a compact outphasing scheme, incorporating a series Chireix combiner and an impedance transformer. Once characterized in a pure output power phase-coding regime, the observed limitation in dynamic range is overcome by operating the amplifiers in a sort of continuous class-J mode, while forcing the load impedance to follow a constant-gain trajectory. A 1c-WCDMA signal, with peak-to-average power ratio (PAPR) of 8.4 dB is shown to be reproduced, satisfying the linearity requirements, with an average efficiency of 58%.