SYSTEM AND METHOD OF AMPLIFIER GAIN CONTROL BY VARIABLE BIASAND DEGENERATION

摘要

A gain control circuit that permits a variable gain amplifier circuit to operate with high input linearity and low power consumption is disclosed. The variable gain amplifier includes a standard differential bipolar transistor input circuit and a pair of degeneration transistors connected to a current source transistor. The gain control circuit provides a variable degeneration control voltage to vary the effective resistance of the degeneration transistors and a variable bias voltage to vary the current of the current source transistor. The input linearity of th e variable gain amplifier is controlled independently of gain by adjusting the effective resistance and t he current in an inverse relationship such that at maximum gain the current is at a maximum while the degeneration resistance is at a minimum, and at minimum gain the current is at a minimum while the degeneration resistance is at a maximum. Therefore the variable gain amplifi er can be controlled to operate with high input linearity and low power at lower ranges of gain.