Design of a low power Variable Gain Amplifier for WLAN standard

Abstract

This paper presents the design of Variable Gain Amplifier (VGA) circuit intended to be used for WLAN receiver. The proposed circuit is composed of two transimpedance amplifiers and a transconductance amplifier. The gain tuning is achieved by using an active resistor. The VGA control is ensured by using a voltage-controlled active resistor VG. The proposed circuit is optimized for low power, low noise and high bandwidth application. This circuit is implemented and simulated using the TSMC 0.18 µm CMOS process device-level description. The studied circuit provided a minimum gain of 6dB and a maximum gain of 51.2dB over more than 66MHz bandwidth. The simulation structure provides less than 17dB of noise figure (NF), an Input Referred Noise (IRN) of around 2.4nV2/Hz, an output Referred Noise (ORN) of around 13.32nV2/Hz and a Third Order Intercept Point measured at the Input (IIP3) of −6dBm. The VGA consumes approximately 70µW under 1.8V power supply.