Variable Gain Amplifier with Accurate Gain
Jianjun Zhou · Modern Electronics Technique · 2009
The variable gain amplifier embedded in an automatic gain control loop is an essential component of GPS recei-ver.With the feedback loop,it constitutes the automatic gain control circuit for ADC to provide constant power signal.VGA gain controlled by analog signal has continuous change,but poor linearity.Resistive negative feedback amplifier is proposed to design a gain range of 0~30 dB intermediate frequency variable gain amplifier.Its gain accuracy nearly does not depend on factors of process,voltage and temperature influence on resistor and MOS switch,gain error less than 0.5% under all corners.Testing results based on 0.18 μm CMOS technical indicates that in-band ripple is less than 0.1 dB,IIP3 is 31 dBm@0 dB,while dissipating 3 mA(containing DC-offset cancellation circuit and CMOS Source-Follower Buffer Circuit).As a result,this amplifier is suitable for the use in analog front-end receiver.