Design of Fast-Settling 40-dB VGA for Closed-loop Current Monitoring System

Abstract

In this paper, a fast-settling Variable Gain Amplifier (VGA) with 40-dB linear-in-decibel gain tuning range is proposed. The VGA is used in a closed-loop current monitoring system and is designed using two cascaded gain cells. The first cell is responsible for the VGA tuning via voltage-to-current control circuit and external resistor with gain range of ±20dB. The second cell’s gain is fixed at 20dB; it is used to stabilize the VGA after adding the common-mode feedback circuit. The VGA is designed using 0.18pm XFAB SOI Technology. Circuit simulations showed that the VGA settling time is 34ns. The VGA’s HD3 is at −73.26dB and its OIP3 of −60dB at maximum gain setting. Comparison with previous work shows that the proposed VGA is faster and has better linearity.