37–43GHz Wide-Band Doherty Power Amplifier with Enhanced AM-PM Characteristic
This paper presents a millimeter-wave (MMW) Doherty power amplifier (DPA) that is designed to achieve high-power efficiency in the back-off (BO) region and enhanced amplitude-to-phase (AM-PM) characteristics over a wide frequency range while minimizing its overall size. Specifically, to enhance the overall linearity of the DPA, the output combiner and the driver stage are both carefully devised to synthesize a complementary nonlinear behavior to that of the main power transistor. Furthermore, vertically stacked transformers are adopted for the implementation of the various matching networks in order to minimize the size and maximize the bandwidth. Accordingly, a proof-of-concept prototype was designed and fabricated using the 45 nm silicon-on-insulator SOI-CMOS process. The measurement results revealed i) a 15 dB small signal gain with ±0.5 dB variation, ii) 20.5 dBm output 1-dB power (OP1dB), iii) 30% and 19% power added efficiency (PAE) at peak and 6 dB BO between 37 and 43 GHz. Furthermore, the measured AM-PM characteristic confirmed phase variation below 2° for output power up to 20 dBm over the entire bandwidth. The testing of the DPA under a 64-QAM 100 MHz signal revealed an error vector magnitude (EVM) of -25 dB and an adjacent channel power ratio (ACPR) of -33 dBc at an average output power and average efficiency of 15.3 dBm and 18.6%, respectively.