A 57–71-GHz Accurate dB-Linear Variable Gain Power Amplifier with Ultralow Gain Error Using Particle Swarm Optimization Algorithm

This paper presents a 57-71GHz low-power variable gain amplifier (VGPA) in a 65nm CMOS process. The proposed VGPA consists of a current-reused variable gain amplifier (VGA) with large accurate dB-linear gain tuning range and a two-stage power amplifier (PA) with high output power and efficiency. To ease calibration and to improve design time efficiency, an optimization algorithm is utilized to calculate the width of VGA transistors. Over 57-71GHz, the measured gain tuning range is 23.5 dB with 0.5-dB step and a peak gain of 22.5 dB. The RMS phase error is from 1.4°to 2.1°and the RMS gain error is less than 0.09 dB over the 3-dB bandwidth. The minimum RMS gain error of 0.05 dB is measured at 62 GHz, demonstrating the best gain accuracy compared to state-of-the-art VGAs. Moreover, the VGPA achieves a peak saturation power (Psat) of 14.4 dBm and a peak power added efficiency (PAE) of 21.5%.