Patent ID: 7746261

Claim:
A variable gain amplifier for amplifying an input voltage at a gain defined by a binary code, comprising: a signal input terminal that inputs the input voltage therein; a signal output terminal that outputs an amplified voltage therethrough; a charge division means that accumulates a charge, divides an accumulated charge according to a predetermined ratio, and accumulates a divided charge again; a charge cumulation means that accumulates a charge, adds or subtracts an accumulated charge with or from the divided charge accumulated in the charge division means, and accumulates a resultant charge again; and a controller that initially executes to accumulate the charge corresponding to the input voltage in the charge division means, executes to accumulate the charge corresponding to the input voltage or a predetermined voltage in the charge cumulation means, executes a charge dividing operation by the charge division means according to each bit of the binary code sequentially from a most significant bit, and executes a charge adding or subtracting operation by the charge cumulation means according to an data value in each bit, wherein the charge division means includes an operational amplifier having an input terminal and an output terminal coupled with the signal output terminal, a first capacitor connectable between the output terminal and the input terminal of the operational amplifier and having one end connectable to the signal input terminal so that the first capacitor accumulates the charge corresponding to the input voltage or the predetermined voltage, and a second capacitor connectable between the output terminal and the input terminal of the operational amplifier so that the second capacitor accumulates the charge without affecting the charge of the first capacitor, the controller executes the charge dividing operation by simultaneously coupling the first and second capacitors between the output terminal and the input terminal of the operational amplifier, the charge cumulation means is provided by the operational amplifier, one of the first and second capacitors, and a third capacitor, the third capacitor is connectable between the output terminal and the input terminal of the operational amplifier so that the third capacitor accumulates the charge corresponding to the input voltage or the predetermined voltage, and the controller transfers the charge accumulated in the first or second capacitor to the third capacitor so that the controller executes the charge adding operation by the charge cumulation means.