Patent ID: 8514017

Claim:
A variable gain amplifier to adjust gain and level of an output voltage, comprising: an input terminal from which an input voltage is input; an output terminal to which the output voltage is output; an operational amplifier, connected to the output terminal, having an inverting input terminal, a non-inverting input terminal, and an output terminal to output the output voltage; an attenuation-rate adjustable feedback circuit, connected to the input terminal, the inverting terminal, and the output terminal of the operational amplifier, to feed back the output voltage from the output terminal of the operational amplifier to the inverting input terminal of the operational amplifier as a feedback voltage, attenuate the output voltage, and output the feedback voltage to the inverting terminal of the operational amplifier; and an attenuation-rate adjustable attenuator, connected to the input terminal and the non-inverting terminal of the operational amplifier, to attenuate the input voltage for outputting the voltage as an attenuated voltage to the non-inverting input terminal of the operational amplifier, the attenuator comprising a digital-analog converter, wherein settings of the attenuation rates of the feedback circuit and the attenuator are combined to increase a resolution of level of the output voltage.