Patent ID: 8525589

Claim:
A pop sound reduction circuit for use in an audio amplifier configured to reduce generation of pop sound at activation or deactivation of the audio amplifier, the pop sound reduction circuit, comprising: a reference voltage circuit configured to generate a reference voltage; a differential amplifier circuit having a first input terminal capable of being applied with the reference voltage generated by the reference voltage circuit as a first input and a second input terminal supplied with an audio signal from an external audio source as a second input, the differential amplifier circuit configured to amplify the audio signal based on a comparison between the first input and the second input; a triangular voltage generator circuit configured to generate a triangular voltage at the activation or deactivation of the audio amplifier; a voltage to current convertor circuit configured to acquire the triangular voltage generated by the triangular voltage generator circuit to generate a current proportional to the triangular voltage; a capacitor configured to be, at the activation of the audio amplifier, charged with the current proportional to the triangular voltage generated by the voltage to current convertor to generate a voltage corresponding to the current proportional to the triangular voltage capable of being applied to the first input terminal of the differential amplifier circuit as the first input; a constant voltage circuit configured to generate a constant voltage; and a control circuit configured to measure, at the activation of the audio amplifier, the triangular voltage generated by the triangular voltage generator circuit and the voltage corresponding to the current proportional to the triangular voltage generated by the capacitor, respectively, and to switch between one of the triangular voltage generated by the triangular voltage generator circuit and the constant voltage generated by the constant voltage generator circuit to be applied to the voltage to current convertor circuit, wherein if the voltage corresponding to the current proportional to the triangular voltage generated by the capacitor has not be raised to reach the reference voltage generated by the reference voltage circuit at a time where the triangular voltage generated by the triangular voltage generator circuit is reduced to be equal to or below a first predetermined voltage, the control circuit switches the triangular voltage generated by the triangular voltage generator circuit applied to the voltage to current convertor circuit into the constant voltage generated by the constant voltage generator circuit to be applied to the voltage to current convertor circuit so as to increase the voltage corresponding to the current proportional to the triangular voltage generated by the capacitor.