Patent ID: 8050428

Claim:
An audio signal transmission circuit comprising: a codec to provide analog audio signals and digital audio signals; an amplifier connected to the codec to receive the analog audio signals, wherein the amplifier includes two input terminals connected to the codec to receive a left-channel and a right-channel of the analog audio signals respectively, and two output terminals to output amplified analog audio signals; a control circuit connected to the codec to receive the digital audio signals and connected to the amplifier to selectively turn off the amplifier; and an output port connected to the amplifier and the control circuit to receive the analog audio signals and the digital audio signals, wherein the output port comprises: a first interface configured to connect to the analog system, the first interface having two input terminals each connected to a corresponding output terminal of the amplifier via a capacitor, and grounded via a resistor; a second interface configured to connect to the digital system, the second interface having a power terminal and a data terminal connected to the control circuit; a grounded reference terminal; a first feedback terminal connected to the control circuit; and a second feedback terminal connected to the control circuit, wherein the first and the second feedback terminals are elastically deformed by a plug of the analog system to contact the grounded reference terminal to turn off the control circuit when the first interface is connected to the analog system, and the first feedback terminal is elastically deformed by a plug of the digital system to contact the grounded reference terminal to turn off the amplifier when the second interface is connected to the digital system.