An Ultra-low Noise Variable Gain Amplifier with Accurate dB-Linear Characteristic

Abstract

In this paper, a high-performance dB-linear variable gain amplifier (VGA) based on gain interpolation is introduced. The VGA core uses a resistor ladder as an attenuator to get different attenuation steps of the input signal. By smoothly moving the gain from one step to the next step, an accurate dB-linear gain characteristic is achieved. A low noise amplifier and a post amplifier are integrated to get lower noise and ensure high linearity, respectively. The chip is fabricated in a 180nm SiGe process and occupies a die area of 1.15mm2. The total gain range is 48dB and the measured gain error is less than 0.27dB. The whole VGA consumes 30mA current from a 5V supply and the bandwidth is 120MHz. The measured in-band input referred noise density is 1nV/√HZ and the measured OIP3 is 33dBm.