A Wideband Reconfigurable CMOS VGA Based on an Asymmetric Capacitor Technique with a Low Phase Variation

Abstract

This paper presents a wideband digitally controlled variable gain amplifier (VGA) with a reconfigurable gain tuning range and gain step in a 65 nm CMOS process. A unique asymmetric capacitor-based reconfigurable technique is proposed to extend the gain tuning range and realize gain step reconfiguration. An active neutralization topology based on a stackless transistor is utilized to compensate for the additional phase shift introduced by the gain tuning. Moreover, a current-type digital-to-analog converter (DAC) is also integrated for easier precise gain control. With the asymmetric capacitor varying from 1000 fF to 200 fF with a step of 400 fF, the proposed VGA achieves a 12.2/9.2/6.1 dB gain tuning range with a 0.4/0.3/0.2 dB gain resolution, respectively. At the maximum gain tuning range mode, the measured minimum root-mean-square (RMS) phase error is 1.7° at 23.4 GHz. At the finest gain step control mode, the RMS phase error measured across 20–30 GHz is lower than 1.9°. The tested result also shows the proposed VGA achieves a peak gain of 13 dB with a 3 dB bandwidth of 21.4–29 GHz, and the output 1 dB compression point (OP1dB) is up to 8.6 dBm at 25 GHz.