Mustafa Özen

High-Efficiency RF Pulsewidth Modulation of Class-E Power Amplifiers

A new switch-mode power-amplifier (SMPA) topology particularly suitable for energy efficient amplification of RF pulsewidth modulation (RF-PWM) signals is derived. It is analytically shown that high efficiency can be maintained over a wide power dynamic range if the imaginary part of the Class-E load impedance is varied along with the duty cycle (pulsewidth). Using the theory developed, an explicit design procedure is presented that allows practical realization of the proposed topology from the circuit and component specifications. Following the design procedure, and using in-house (Chalmers University, Göteborg, Sweden) SiC varactor diodes to implement the tunable imaginary load impedance, a 2-GHz 10-W peak output power GaN HEMT circuit demonstrator is realized. RF-PWM input signals for characterization of the prototype power amplifier (PA) is generated with a dedicated 65-nm CMOS modulator. The measurements show that a drain efficiency >; 70% can be obtained over an 6.5-dB dynamic range, which verifies the theory presented and demonstrates the feasibility of the proposed PA topology.

Continuous Class-E Power Amplifier Modes

In this brief, a continuum of novel closed-form solutions is derived for class-E power amplifiers (PAs). It is analytically proven that the class-E zero voltage/zero voltage derivative switching conditions can be satisfied for an arbitrarily selected reactive second harmonic switch impedance (<i>Z</i>₂^S). The higher order harmonic currents are terminated capacitively. The conventional class-E, class- <i>E</i>/<i>F</i>₂, and class-<i>EF</i>₂ modes are thus subsets of the continuum. The arbitrary selection of <i>Z</i>₂^S enables robust waveform engineering for performance optimization in specific applications. Furthermore, the theoretical derivation provides important possibilities for wideband class-E PA synthesis.

Symmetrical doherty amplifier with high efficiency over large output power dynamic range

For the conventional Doherty power amplifiers, asymmetrical cells are used to achieve high efficiency over large (> 6 dB) output power dynamic ranges, i.e. larger class-C cell. In this paper, it will be theoretically proven that high efficiency over large dynamic ranges also can be achieved using symmetrical devices, while still maintaining full voltage and current swing of both transistor cells. Using a smaller class-C cell compared to the asymmetrical Doherty has the advantages of higher gain and power added efficiency (PAE). The proposed symmetrical Doherty concept is experimentally verified by a 3.5 GHz 28 Watt circuit demonstrator fabricated using identical GaN HEMT devices. An average power added efficiency of 52% and adjacent power leakage ratio of -52 dB is obtained with 9 dB peak-to-average power-ratio 20 MHz LTE test signals.

Doherty's Legacy: A History of the Doherty Power Amplifier from 1936 to the Present Day

Eighty years ago, William Doherty invented a PA architecture that has played-and will continue to play-an important role in the development of energy-efficient radio transmitters for a variety of wireless communication applications. Although the original concept is still equally valid, the development of new semiconductor processes and digital signal processing techniques has served as a basis for an evolution of the DPA topology into the 21st century. The need for energy-efficient power amplification will be further emphasized in future wireless systems (5G and beyond) through the projected exploration of dense-antenna arrays and millimeter-wave frequencies. Recent developments of the Doherty concept make it one of the most attractive candidates for realizing energy-efficient wireless systems into the future.

High efficiency RF pulse width modulation with tunable load network class-E PA

In this paper, a 10 W peak power 2 GHz highly efficient RF pulse width modulation (RF-PWM) based transmitter is presented. RF-PWM signals are generated with a dedicated 65 nm CMOS modulator and subsequently amplified with a GaN Class-E power amplifier (PA). The modulator use extended drain MOS (EDMOS) high voltage transistors to provide the required voltage swing to drive the GaN used as a switch. The imaginary load impedance of the Class-E is electronically tunable and is implemented with in-house high breakdown voltage SiC varactors. The tunable imaginary load impedance enables optimization of the Class-E versus the duty cycle (pulse width). The peak efficiency is therefore preserved over a wide range of output power levels. The measured drain efficiency of the Class-E output stage is above 70% over a 6.5 dB output power dynamic range. The overall transmitter efficiency is above 60% for the same dynamic range.

Outphasing combiner synthesis from transistor load pull data

A novel load-pull based outphasing combiner synthesis approach is developed. The design technique is based on the derivation of combiner network parameters in terms of the optimal load impedances at the peak power level and a predefined back-off level. The combiner is then synthesized using transmission lines or lumped element networks. The design technique is verified in a 30 W GaN HEMT outphasing transmitter demonstrator. The prototype presents a power-added efficiency of 50% at 2.1 GHz with 9 dB peak-to-average power ratio (PAPR) 20 MHz LTE signals. The related measured adjacent channel leakage ratio is -51 dBc using a low complexity digital pre-distortion linearization algorithm.

Low Phase Noise GaN HEMT Oscillators With Excellent Figures of Merit

This letter presents guidelines for the design of low phase noise oscillators in GaN high electron mobility transistor (HEMT) technology. The design starts from bias-dependent low-frequency (LF) noise measurements. Oscillator topology and bias point are then chosen for operation in regions where LF noise is low. The best LF noise properties are obtained for low drain voltage and current. Thus, the low phase noise can be achieved at low dc power which also means that power normalized phase noise figure of merit (FOM) will be good. Two different oscillators have been designed and measured. A 9.9 GHz common-gate balanced Colpitts oscillator operating in class C presents a phase noise of -136 dBc/Hz@1 MHz. The result is achieved for Vd =6 V and Id = 30 mA, giving FOM = 193 dBc/Hz. A 1.95 GHz negative-resistance oscillator operating in switched mode presents a phase noise of of -149 dBc/Hz@ 1 MHz offset. With drain voltage and current of Vd = 4 V and Id = 100 mA, this oscillator presents FOM = 189 dBc/Hz. To the best of the authors knowledge, these two oscillators present the highest reported FOM for GaN HEMT oscillators.

A Doherty Power Amplifier Design Method for Improved Efficiency and Linearity

A novel Doherty power amplifier (PA) design method enabling high efficiency and high linearity simultaneously is proposed. The output combiner network is treated as a black box, and its parameters, together with the input phase delay, are solved based on given transistor characteristics and design requirements. This opens for new PA solutions with nonconventional Doherty behavior. The increased design space enables new tradeoffs in Doherty PA designs, including solutions with both high efficiency and high linearity simultaneously. A method utilizing the new design space is developed. For verification, a 20-W 2.14-GHz symmetrical gallium nitride high electron mobility transistors Doherty PA is fabricated and measured. The PA obtains an average power added efficiency of 40% and an adjacent power leakage ratio of -41 dBc without any linearization for an 8.6-dB peak to average power ratio 10-MHz-long term evolution signal, at an average output power of 35.5 dBm.

Wideband and efficient watt-level SiGe BiCMOS switching mode power amplifier using continuous class-E modes theory

In this paper, a generic, wide-band switch mode power amplifier (SMPA) design approach is developed based on the continuous class-E modes theory. A watt level, 1.3-2.2 GHz SiGe BiCMOS class-E SMPA is realized for experimental verification. The prototype provides collector efficiencies higher than 70% and output power levels higher than 29 dBm across 1.3-2.2 GHz band, fully confirming the validity of the proposed design approach.

A class-J power amplifier with varactor-based dynamic load modulation across a large bandwidth

A novel class-J operated power amplifier (PA) utilizing varactor-based dynamic load modulation is presented. It is theoretically shown that the proposed PA can maintain high average efficiency across more than 35% RF bandwidth by means of a purely reactive load modulation after the transistor output capacitance. The theory is experimentally verified by a 15 W GaN HEMT PA operating from 1.80 to 2.20 GHz, using SiC varactors as dynamically tunable load elements. In the band, the PA presents a power added efficiency (PAE) higher than 39% at 6 dB output power back-off. For a 3.84 MHz W-CDMA signal with 6.7 dB peak to average power ratio, an average PAE higher than 39% and an adjacent channel leakage ratio below -45.8 dBc are obtained across the entire band after linearization.