GaN HEMT-based hybrid current-mode class-S power amplifier for 955 MHz LTE signal

This article presents a gallium nitride-based hybrid current-mode class-S (CMCS) power amplifier (PA) in conjunction with a realized band-pass delta-sigma modulator for 955 MHz long-term evolution (LTE) signal. Commercial surface mount Schottky diodes are located behind switching transistors to protect them against negative voltage swing, and performances are analyzed from the perspective of the variations of the output voltage and current waveforms by the intrinsic components of diode. In particular, the chip-on-board technique is adopted to enhance the drain efficiency, and the differential output filter and balun composed of lumped LC resonators are integrated at the back of the switching transistor to extract amplified LTE signal. From the measured results with an 8.5 dB peak to average power ratio 3G LTE 10 MHz input signal, the proposed CMCS PA shows maximum average output power of 37.1 and 32.2 dBm, and the resulting drain efficiencies of 35.5 and 38.5% with the drain voltage of 20 and 10 V, respectively.