Patent ID: 8289076

Claim:
An amplifying circuit that is operated by a single power supply, connectable to a voltage source and grounding potential, comprising: a reference voltage generating section for generating a reference voltage to be supplied to a negative-side input terminal of a load based on a power source voltage to be supplied from the voltage source; an amplifying circuit for amplifying an input signal and outputting the signal to a positive-side input terminal of the load, the amplifying circuit being operated by the power source voltage to be supplied from the voltage source; a threshold voltage generating section for generating a first threshold voltage normally higher than the reference voltage and a second threshold voltage normally lower than the reference voltage based on the power source voltage to be supplied from the voltage source; and a detecting section for comparing the reference voltage with the first threshold voltage and comparing the reference voltage with the second threshold voltage, outputting a signal representing that an output voltage from the amplifying circuit includes a DC voltage when the reference voltage is not less than the first threshold voltage or the reference voltage is not more than the second threshold voltage, and outputting a signal representing that the output voltage from the amplifying circuit does not include a DC voltage when the reference voltage is lower than the first threshold voltage and the reference voltage is higher than the second threshold voltage.