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

Lingshan Kong,Pui-In Mak,Rui P Martins,Haohong Yu,Yong Chen,Chirn Chye Boon

doi:10.1109/access.2021.3062360

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 mm 2 (0.024 mm 2 ) 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 2 7 -1 PRBS input at 12 Gb/s. Their power efficiencies (1.83 and 1.67 pJ/bit) compare favorably with state-of-the-art.

Highlights

Dynamic range is an important aspect of both wireless and wireline communication systems
Gain tuning technique has been implemented with various building blocks, such as low noise amplifier (LNA) [3], power amplifier (PA) [4], trans-impedance amplifier (TIA) [5], [6], etc., incorporating variable gain amplifier (VGA) is still the most efficient way to boost the dynamic range
Different from the traditional current-steering VGAs, as shown in Fig. 1(c), our proposed design adjusts the transconductance of the input transistors directly, instead of manipulating with the cascode device

Summary

INTRODUCTION

Dynamic range is an important aspect of both wireless and wireline communication systems. To implement a differential current-control signal, one popular way is to use the architecture shown, whose load and input transistor share a total current This structure is efficient in a way that changes the gm and output resistance simultaneously, but the bandwidth keeps changing when the gain is tuned. Two continuously varying currents can be obtained from one single-ended control voltage, which could be used to adjust the transconductance (gm) of the transistors and the gain of the amplifier To implement this control method into VGA design, both standalone and integrated gain-control topologies are developed later

IMPLEMENTATION WITH STANDALONE GAIN-TUNING TOPOLOGY

COMPLETE ARCHITECTURE

MEASUREMENT RESULTS

CONCLUSION