Wideband Variable-Gain Amplifiers Based on a Pseudo-Current-Steering Gain-Tuning Technique

Abstract

This paper reports two variable-gain amplifiers (VGAs) featuring a new pseudo-current-steering gain-tuning technique. In the first VGA (VGA-I), a single-voltage-controlled dual-branch current mirror is developed as a standalone gain control block. In the second VGA (VGA-II), two NMOS transistors, which are biased by a tunable voltage, are integrated into a conventional common-source amplifier to steer away from a part of the total current. Meanwhile, the theoretical analysis is developed to reveal the mechanism of different gain tuning. Fabricated in a 40-nm CMOS process, VGA-I (VGA-II) occupies a tiny area of 0.03 mm2 (0.024 mm2) and consumes 22 mW (20 mW). Measured over a gain range of >64 dB, the -3-dB bandwidth of VGA-I (VGA-II) is 9 GHz (6.6 GHz). For the time-domain tests, VGA-I (VGA-II) exhibits a jitter of 40 ps (30 ps), under a 27-1 PRBS input at 12 Gb/s. Their power efficiencies (1.83 and 1.67 pJ/bit) compare favorably with state-of-the-art.