Reinel Marante

A Linear Assisted Switching Envelope Amplifier for a UHF Polar Transmitter

Spectrally efficient wireless communication standards impose stringent linearity specifications, which would require traditional IQ transmitters to operate with back-offed and power inefficient linear RF power amplifiers (PAs). In order to overcome such a significant limitation, alternative architectures have been proposed, as those based on the envelope elimination and restoration technique. An example of the application of this technique is the polar transmitter. In this paper, a UHF polar transmitter is presented, combining switching and linear stages in the envelope amplifier as to achieve both wide bandwidth and high efficiency, when drain modulating a GaN HEMT Class E RF PA. Several tests, using EDGE, TETRA, and WCDMA standards have been performed with good results.

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 1 GHz frequency-controlled class E 2 DC/DC converter for efficiently handling wideband signal envelopes

In this paper, a 1 GHz class E2 DC/DC converter, implementing a frequency-modulation (FM) control, is proposed for efficiently handling wideband wireless signal envelopes. Properly terminating the inverting and rectifying GaN HEMT devices, a nearly linear output voltage versus switching frequency profile is obtained, with 70% efficiency at a voltage value 5.1 dB below the peak. Incorporating a Voltage Controlled Oscillator (VCO) and a gate-driving amplifier, the large-signal bandwidth (BW) and slew rate have been estimated to be around 20 MHz and 720 V/μSeg, respectively. The FM converter is also shown to offer a good dynamic reproduction of 6.6 dB peak-to-average power ratio (PAPR) 2- and 4-carrier WCDMA envelope signals, with average efficiencies over 60%. Employed as envelope modulator in a pure polar architecture, handling a 5 MHz hole-punched multisine signal, a 6.7 W output power has been obtained with a transmitter efficiency of 56%.

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.

A UHF outphasing transmitter based on class E power amplifiers

In this paper, an outphasing transmitter operating at UHF band (770 MHz) is presented, based on highly efficient Class E RF power amplifiers (PAs). Implemented on GaN HEMT technology and following a load modulation path close to the optimum, a simple lumped-element Chireix combiner allows obtaining an efficiency value over 60% along a 7 dB output power range. Spectrally efficient digital modulation formats, with nulls in the envelope, may be handled by means of a hybrid technique, combining outphasing modulation with envelope variation of the RF excitations. Average drain efficiency and PAE values of 68.6% and 66.2%, respectively, have been measured, for a 14 W WCDMA signal with a 5.06 dB PAPR, while meeting ACPR specifications.

Temperature dependent memory effects on a drain modulated GaN HEMT power amplifier

In this paper, the impact of self heating on the linearity of a drain modulated GaN HEMT power amplifier (PA) is studied. After characterizing the frequency response of junction temperature rise to power dissipation, as well as the effect of this variable on the PA modulation profiles, the dynamic envelope trajectory, under a two-tone test signal, appears to be slightly dependent on frequency spacing. Self heating related effects are shown to be negligible in presence of other nonidealities, as the case of feedthrough. In this way, punching a vector hole in the two-tone I/Q diagram and applying memoryless digital predistortion (DPD), will allow identifying the influence of self heating effects, over adjacent channel distortion. Finally, this long-term memory effect is proved to be responsible for only a minor residual distortion in a linearized EDGE polar transmitter.

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.

Nonlinear characterization techniques for improving accuracy of GaN HEMT model predictions in RF power amplifiers

In this paper, two vector nonlinear characterization procedures are presented, aimed at improving available GaN HEMT models for an accurate reproduction of the device behavior operating as a current source and in switched-mode RF power amplifiers (PAs). In the case of the more traditional linear amplifying classes, a technique for simultaneously extracting the higher order derivatives of the Ids(Vgs), Igs(Vgs) and Cgs(Vgs) transistor nonlinearities, along a desired load line, is described. This procedure conveniently isolates and models their contributions to the device intermodulation distortion (IMD) behavior. In the case of highly efficient switched-mode PAs, employed under drain modulation condition, a modified procedure for isodynamically measuring the higher order derivatives of the Vdd-to-AM and Vdd-to-PM amplifier profiles is put into consideration, as a way to refine the triode region reproduction for ON-OFF operation. The test set-ups, based on the combination of vector signal analysis and vector signal generation capabilities, are described in detail, together with some analytic expressions for the parameter extraction. Measured results for a 15 W device from Cree are finally included.

Impact of R on (V DD ) dependence on polar transmitter residual distortion

In this paper, the particular impact of switching device ON resistance variation with drain supply voltage, Ron(VDD), on polar transmitter distortion is considered. Pulsed I/V measurement results over a GaN HEMT are used to predict the deviation in the Vdd-to-AM modulation profile. System-level calculations, in the presence of other nonidealities, allow the evaluation of the relative contribution of this frequency dispersion related effect.