Michael Litchfield

X-band MMIC GaN power amplifiers designed for high-efficiency supply-modulated transmitters

The design and measured performance of X-band power amplifier MMICs that utilize 0.15μm GaN on SiC process technology are presented. Under continuous wave operating conditions these single and 2-stage MMICs demonstrate peak power added efficiencies (PAE) from 45% to 69%, output powers from 2.5-13W, and up to 20dB of large signal gain. Designed for drain modulated applications, the power amplifiers maintain good performance at reduced drain bias voltage. The output power of the two stage MMIC can be varied from 2W to 13W when the drain bias is varied between 7.5V and 20V while maintaining a PAE above 54%.

High-Efficiency X-Band MMIC GaN Power Amplifiers Operating as Rectifiers

This paper presents a performance evaluation of GaN X-Band power amplifiers operating as self-synchronous rectifiers. Two single-stage MMIC power amplifiers are characterized under continuous wave conditions at 10.1GHz. One PA is designed with a single 10 × 100μm HEMT in a 0.15μm GaN process, while the other contains two 10 × 100μm power-combined devices. The MMICs exhibit 67% and 56% power added efficiency at VDD = 20V in deep class-AB bias, respectively. In rectifier mode, biased in class-C, the same MMICs show a RF-to-DC efficiency of 64%. The output powers of the two MMIC PAs are around 3.2W. In rectifier mode, the gate DC bias and the load-pull determined RF gate impedance are set for optimal efficiency. The DC load does not affect the efficiency substantially, and can be chosen for a desired voltage or current. The paper demonstrates that high-power efficient GaN rectifiers can be achieved by designing high-efficiency PAs at least up to X-band.

Multi-Level Chireix Outphasing GaN MMIC PA

This paper presents the design and performance of a 9.7 GHz GaN MMIC Chireix outphasing PA with discrete supply modulation. This architecture is referred to as Multi-Level Chireix Outphasing (ML-CO). The internal PAs include class-F harmonic terminations, while the Chireix combiner provides the fundamental frequency load modulation. A peak output power of 37 dBm (5W) is achieved, while a peak ηtot of 60.2 % is reached at 35.7 dBm. The average total efficiency calculated for a 6 dB PAR QPSK signal is 48.1 %, a 15.5 point improvement over the constant supply case.

Load Modulation Measurements of X-Band Outphasing Power Amplifiers

This paper presents an in-depth investigation of both isolated and non-isolated outphasing power amplifiers, with and without supply modulation. X-band GaN MMIC power amplifiers with 70% power-added efficiency and 2.7 W output power at 10.1 GHz are configured in hybrid outphasing circuits with several combiners that include bi-directional couplers, enabling calibrated measurements of internal load modulation. It is experimentally demonstrated that the load modulation critically depends on the power balance of the two internal MMIC PAs. Despite the additional loss in the combiner, peak total efficiencies greater than 47% are achieved by full outphasing PAs with more than 3.7 W of output power. A comparison between several outphasing configurations quantifies the improvement in efficiency for both isolated and non-isolated outphasing PAs with supply modulation.

X-Band GaN Multi-Level Chireix Outphasing PA with a Discrete Supply Modulator MMIC

This paper presents the characterization of a multi-level Chireix outphasing PA with a GaN discrete supply modulator MMIC at 9.7GHz. The internal PAs include class-F harmonic terminations, while the Chireix combiner determines the fundamental frequency load modulation. A power-DAC architecture provides 8 supply levels with 3 half-bridges, maintaining more than 85% efficiency. The combination of the two achieves a peak output power of 4.8W, and average total efficiencies for a 6dB PAR QPSK signal of 44.1% and 48.1% with and without considering the supply modulator consumption, respectively, demonstrating the feasibility of this PA architecture with a real discrete supply modulator.

X-band outphasing GaN MMIC PA with power recycling

We demonstrate an outphasing GaN MMIC PA with power recycling operating at 10.35 GHz. The MMIC includes high-efficiency PAs, a miniaturized rat-race combiner, and a high-efficiency, self-synchronous transistor rectifier. A peak total efficiency of 65.2% is achieved with 6W of output power. Up to 2.24W of rectified power improves total efficiency by up to 6.5 points at -3.5 dB normalized output power, matching presented theory.

Efficient transmitters and receivers for high-power wireless powering systems

The efficiency of a wireless powering system is maximized when the power transmitter power-added efficiency (PAE), power receiver conversion efficiency (ηC) and wireless coupling efficiency (ηW) are maximized. This paper focuses on a general approach to the design of an efficient transmitter and receiver of a high-power wireless powering system, which is valid for any type of wireless power coupling. Experimental results for high-efficiency power transmitters and receivers at various frequencies and with various power levels are discussed.

A MMIC/hybrid high-efficiency X-band power amplifier

This paper presents design and measurements of a X-band high-efficiency MMIC/hybrid PA implemented in the TriQuint 0.25-um GaN on SiC pHEMT process. In the absence of a nonlinear model valid for high-efficiency classes of operation, an output network with specific harmonic terminations is included in the MMIC, allowing for external fundamental load-pull only. The results show a power added efficiency (PAE) of 71% % with a saturated gain of 12 dB and output power of 3 W, or 4.5 W/mm, at 9.8 GHz in CW operation.

Multi-level supply-modulated Chireix outphasing for LTE signals

This work presents a dynamic characterization of a multi-level Chireix outphasing (ML-CO) power amplifier (PA) with modulated signals. The ML-CO technique combines the advantages of envelope tracking and outphasing architectures by limiting the supply modulation to discrete levels (enabled by an efficient power DAC modulator) and using outphasing for fine amplitude control. We describe the development of an experimental test bench able to supply phase- and time-aligned modulated signals for outphasing and supply modulation simultaneously. Pulse characterization is used to design a multilevel memory-less polynomial DPD. The linearized ML-CO PA is demonstrated with 1.4 MHz and 10 MHz LTE signals at 9.7 GHz. For both signals, the average total power consumption is reduced by a factor of two when supply modulation is used. For the 9.3 dB PAR, 1.4 MHz signal the PA operates with 38% average drain efficiency at 0.54 W average output power.

Microwave Transistor Power Rectifiers and Applications

This paper presents design, analysis and experimental results on synchronous and self- synchronous microwave transistor rectifiers implemented with GaN HEMTs at frequencies from 2 to 10GHz. The rectifier/power amplifier duality is explained and measurements confirming this mode of operation are presented. Finally, rectifier applications in wireless power transfer and high- frequency integrated dc-dc converters are discussed, including a GaN MMIC dc-dc converter switching at 4.6GHz.