Patent ID: 6788144
Filing Date: 2004-09-07
Classification: H03F

Abstract:
A variable-gain amplifier comprising:a differential current output circuit that outputs a first current and a second current as differential currents corresponding to a first input signal, a first current converter that converts the first current into a third current at a current conversion rate corresponding to a second input signal and outputs the third current to a first node, a second current converter that converts the second current into a fourth current at a current conversion rate corresponding to the second input signal and outputs the fourth current to a second node, a first load resistor connected between the first node and a third node, a second load resistor connected between the second and third nodes, and a voltage-adjustment circuit that acts as an adjustable resistor between the voltage supply terminal and the third node wherein the voltage-adjustment circuit has a pair of differential transistors to which the second input signal is supplied as a differential signal, where one of the transistors supplies a current corresponding to the second input signal to the third node such that the voltages at the first and second nodes do not change as the second signal varies.