Dual-tuned high-swing variable-gain amplifier with enhanced dB-linear control

Abstract

In this work, an analog-controlled variable gain amplifier (VGA) is proposed that demonstrates high linearity across a wide range of control voltages and low noise for analog front-end receivers. This work presents a dual-tuning technique utilizing diode-connected P-MOS load and pseudo-exponential approximation based source degeneration (DCPL-PESD), which enables simultaneous tuning of different control voltages to achieve the required dB-linear characteristic. The gain is increased by cross-coupling the input transistors of the differential pair. To extend the gain range, three single-stage VGAs are cascaded. The design and implementation of this VGA were carried out using the Cadence Virtuoso tool in 180 nm CMOS technology. Post-layout results indicate that the 3-stage cascaded VGA offers a gain range of 67.5 dB, of which 55 dB is dB-linear. By tuning the control voltage VC, it provides a continuous 18 dB dB-linear gain. The overall VGA consumes 0.232 mA from a 1.8 V power supply, with a power consumption of 417 μW. The bandwidth of 3-stage VGAs is measured as 46 MHz. The minimum input-referred noise (IRN) of this VGA is 4.158 nVHz. The total area, including the bias circuit and buffer, is 0.0054 mm2, and the output 1 dB compression point is −2.83 dBm at the gain of −1 dB.