Patent ID: 7504973

Claim:
A gain-variable analog/digital converter comprising: a reference voltage generation circuit unit for generating voltage values of reference voltages at a high-voltage side and a low-voltage side, on the basis of a current outputted from a current source circuit and an impedance value of an impedance circuit, which circuits are connected to an operating amplifier; an analog/digital conversion circuit unit for converting an inputted analog signal into a digital signal on the basis of the high-voltage side and low-voltage side voltage values of the reference voltages that are generated by the reference voltage generation circuit unit; and a digital signal processing unit (DSP) for judging whether gain adjustment for the analog/digital conversion is necessary or not on the basis of an output signal from the analog/digital conversion circuit unit, and outputting an output signal for changing the output current of the current source circuit or the impedance value of the impedance circuit when it is judged that gain adjustment is necessary; wherein the output current of the current source circuit or the impedance value of the impedance circuit is changed on the basis of the output signal of the DSP to adjust the high-voltage side or low-voltage side voltage value of the reference voltage that is generated from the reference voltage generation circuit unit, thereby making the gain of the analog/digital conversion variable.