Patent ID: 8081774

Claim:
A circuit for eliminating pop sounds at power on and off, comprising: a switch, which has a first input terminal connected to a low voltage and a second input terminal connected to a reference voltage for switching at power on or off; a feedback network, which is connected to the switch in order to provide a feedback current and comprised of a first resistor and a second resistor, the second resistor having a first terminal connected to the switch and a second terminal connected to a first terminal of the first resistor; an operational amplifier, which has a negative input terminal connected to the first terminal of the first resistor and the second terminal of the second resistor and has an output terminal connected to a second terminal of the first resistor; and an output network, which has an output terminal, a third resistor, a fourth resistor and a capacitor, the third resistor having a first terminal connected to the output terminal of the operational amplifier and a second terminal connected to the output terminal of the output network, a first terminal of the fourth resistor, a first terminal of the capacitor and a positive input terminal of the operational amplifier, the fourth resistor having a second terminal connected to the low voltage, the capacitor having a second terminal connected to the low voltage; wherein, when the switch is connected to the low voltage, the output terminal of the output network provides an operating bias, which is gradually increased, to the circuit, and the output terminal of the output network provides the operating bias, which is gradually reduced, to the circuit when the switch is connected to the reference voltage.