Broadband Fully Integrated GaN Power Amplifier With Minimum-Inductance BPF Matching and Two-Transistor AM-PM Compensation

In this paper, we present a design technique for broadband fully integrated GaN power amplifiers (PAs), with merged bandpass filter (BPF) and AM-PM compensation. The minimum-inductance BPF structure is used as the output matching network of the PA. A new theory of the minimum-inductance BPF is developed and it is shown that, compared to the standard BPF, it can be implemented using lower total inductance and provide higher out-of-band attenuation. Furthermore, using a two-transistor architecture, an AM-PM compensation technique is proposed where compressive and expansive nonlinearity profiles of the transistors' transconductance and gate-source capacitance are combined to achieve a linear total transconductance and input capacitance, over a wide power range. A fully integrated PA prototype, implemented in a 0.25-mu m GaN-on-SiC process with 28-V supply, provides 35.1-38.9dBm output power, 45-61% drain efficiency (DE), 40-55% power-added efficiency (PAE), and 11.3-13.4dB power gain, across 2.0-4.0GHz. For a 256-QAM signal with 7.2-dB PAPR and 100-MHz bandwidth at 2.4GHz, it achieves 2.5% (-32.0dB) rms error vector magnitude (EVMrms) and -37.5/-37.6dBc adjacent channel leakage ratio (ACLR), while average output power and DE/PAE are respectively 30.1dBm and 20.6/ 19.5%, without predistortion. EVMrms and ACLR can be improved to 0.5% (-46dB) and -46.4/-46.8dBc by using digital predistortion (DPD).