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Flexible GaN MMIC Enabling Digital Power Amplifiers for the Future Wireless Infrastructure

FBH research: 04.06.2015

Realized H-bridge VM class-D/S PA

Fig. 1. Realized H-bridge VM class-D/S PA; size: 68x42x15 mm3

Output power, final-stage drain efficiency and overall PAE vs. input power back-off

Fig. 2. Output power, final-stage drain efficiency and overall PAE vs. input power back-off; input signal: 1-tone PWM signal

Today’s and next-generation wireless communication infrastructure demands for high flexibility, low cost, and high efficiency. As base stations are mostly realized as digital systems, the RF power amplifier (PA) represents the last analog part in the transmitter chain. However, the growing demands towards wideband, multi-band, and multi-standard features together with the progress in semiconductor technology have been fueling research on non-analog PA realizations within the last years. The ultimate target of these efforts is the fully digital transmitter. The key component in realizing such a concept is the active component.

Recently, FBH presented at the IEEE International Microwave Symposium 2015 in Phoenix a new highly flexible, high-gain and highly efficient 4-stage GaN voltage-mode (VM) PA MMIC and its potential as a building block for digital PA applications. To prove versatility and compactness, the same chip is used in two examples to build a single-chip and an H-bridge class-S PA for the 800 MHz band (LTE standard), the latter includes the option for digital Doherty operation.

Output powers up to 14 W with final-stage drain-efficiencies (ηdrain) of 70%…80% were reached. Overall power-added efficiency (PAE) of up to 47% and a large-signal gain of maximum 40 dB were achieved. By applying the digital Doherty approach to the H-bridge configuration ηdrain-values of 75% and 40% at 6 dB and 12 dB power back-off were reached, respectively.

The results demonstrate the benefits of the digital PA approach in realizing various circuit types with the same IC by just changing the periphery. Moreover, this includes further options, in particular change of signal frequency and multi-band operation.

Publication

A. Wentzel, S. Chevtchenko, P. Kurpas, and W. Heinrich "A Flexible GaN MMIC Enabling Digital Power Amplifiers for the Future Wireless Infrastructure" IEEE MTT-S Int. Microw. Symp. Dig., Phoenix, USA, May 17-22, TH2B-5 (2015).