**5.4. Variable Gain Amplifier**

Variable gain amplifier (VGA) is an essential block at the front end of ultra-wideband transceiver to maximize the dynamic range of the receivers. VGAs are also used in the transmitter part of ultra-wideband transceivers to control the transmission signal power. The VGA is typically implanted in an automatic gain control amplifier (AGC) loops to provide constant output signal regardless the variations in the input signal. The variable gain amplifier suppresses even harmonics, rejects common-mode noises and provides good linearity and wideband performance regardless of the control voltage.
