Hybrid Current-Mode Class-S Power Amplifier With GaN Schottky Diode Using Chip-On-Board Technique for 955 MHz LTE Signal

This paper presents a gallium nitride (GaN)-based hybrid current-mode class-S (CMCS) power amplifier (PA) using a bandpass delta-sigma modulator (BPDSM) for a 955-MHz LTE signal. To enhance the drain efficiency of the CMCS PA, the chip-on-board (COB) technique, which can reduce the external parasitic components of the packaged transistor and allow fast switching operation at high frequencies by minimizing distortion of the pulse waveform, is adopted. Also, GaN Schottky barrier diodes are fabricated in-house to protect the switching transistor against the high negative voltage swing. 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 output rectangular waveform, and the fabricated CMCS PA is measured and analyzed at four different states of BPDSM according to the coding efficiency from different input power level to obtain higher power and efficiency. Finally, a cavity bandpass filter (BPF) is added to the output circuit for a more accurate reduction of the harmonics and out-of-band noise signals to enhance system efficiency. From the measured results for an 8.5-dB PAPR 3 G LTE 10-MHz input signal, the proposed CMCS PA has a maximum average output power of 37.61 and 30.78 dBm, and the resulting drain efficiencies of 33.3% and 38.6% with the drain voltage of 19 and 7 V, respectively.