A gain boosting method at RF frequency using active feedback and its application to RF variable gain amplifier (VGA)

A new method to achieve high voltage gain in RF-frequency range is proposed. The method adopts cascoded active feedback scheme with cascode amplifier to convert the behavior of a cascoding transistor from common gate type to quasi-common source operation. By this method, we acquire high voltage gain and increased 3 dB bandwidth simultaneously with less power consumption compared to conventional cascode amplifier. Using this technique, we propose a new differential RF variable gain amplifier (VGA). By control the feedback network, this new RF VGA shows variable gain range from 5 dB to 20 dB for single stage at 2.1 GHz. The VGA has three gain modes and variable gain step is approximately 7 dB. The used bias current is less than 1.2 mA for each differential path. All circuit simulations are based on 0.25 μm CMOS technology with 3 V supply voltage.