An Accurate dB-Linear CMOS VGA Based on Double Duplicate Biasing Technique

In this letter, a variable-gain amplifier (VGA) cell with an accurate dB-linear characteristic is proposed. By adopting a double-duplicate-biasing technique, this VGA cell achieves simple but effective continuous dB-linear gain control. The VGA cell features wide bandwidth, small chip area, and low power consumption. Based on the proposed VGA cell, we implement a fully differential three-stage VGA with dc-offset cancellation. This three-stage VGA is fabricated in a 0.13-μm CMOS technology with a core area of 0.1 mm2. The measurement result shows the proposed dB-linear VGA presents gain-tuning range from -21 dB to 20 dB with dB-linear error of about 0.6 dB. At the maximum gain setting, an output P1dBof -12 dBm and a noise figure of 27 are measured. The -3-dB bandwidth of the VGA is 580 MHz, and the core circuit consumes about 4.15 mA from a single 1.2-V supply.