Patent ID: 7224010

Claim:
A voltage-controlled amplifier for a signal processing system, comprising: an input voltage reception end for receiving an input voltage; a first voltage-to-current converter coupled to the input voltage reception end, for outputting a first current according to the input voltage received by the input voltage reception end; a reference current generator for generating a second current; a gain adjustment circuit coupled to the first voltage-to-current converter and the reference current generator, for receiving the first current and the second current, and adjusting a gain of the voltage-controlled amplifier, the gain adjustment circuit comprising: a first bipolar junction transistor comprising a collector, a base end, and an emitter; a second bipolar junction transistor comprising a collector, a base end, and an emitter; a third bipolar junction transistor comprising a collector, a base end, and an emitter; a fourth bipolar junction transistor comprising a collector, a base end, and an emitter; and a control voltage reception circuit comprising an end coupled to the base end of the second bipolar junction transistor and the base end of the third bipolar junction transistor, and another end coupled to the base end of the first bipolar junction transistor and the base end of the fourth bipolar junction transistor, for outputting a control voltage; a first current mirror coupled to the first voltage-to-current converter, the gain adjustment circuit, and the reference current generator, comprising: a reference branch coupled to an output end of the first voltage-to-current converter, for transmitting the first current; a drain branch coupled to the reference current generator, the emitter of the first bipolar junction transistor and the emitter of the second bipolar junction transistor, for draining a current equal to the first current from the emitter of the first bipolar junction transistor and the emitter of the second bipolar junction transistor; and a mirror branch coupled to the emitter of the third bipolar junction transistor and the emitter of the fourth bipolar junction transistor, for providing a current equal to the first current for the emitter of the third bipolar junction transistor and the emitter of the fourth bipolar junction transistor; and an output circuit coupled to the gain adjustment circuit, for determining a difference value between a current of the collector of the first bipolar junction transistor and a current of the collector of the fourth bipolar junction transistor, for outputting an output voltage; wherein the output voltage outputted from the output circuit is controlled according to the control voltage outputted from the gain adjustment circuit.