Patent ID: 8824512

Claim:
An interface circuit comprising: a first receiving unit configured to receive a first differential signal received from an external device through a transmission line, the first receiving unit comprising a first addition unit configured to add the first differential signal to an inverted signal and output a second differential signal, wherein the inverted signal is an inversion of a first signal output from an amplifier which receives a third signal as input, wherein the second differential signal is substantially the first differential signal with the first signal removed therefrom; a second receiving unit comprising a second addition unit configured to extract a common-mode signal from the first differential signal; a transmitting unit configured to provide the third signal as input to the amplifier, and to transmit the first differential signal to the external device through the transmission line; and a communication circuit that communicates with the external device via a pair of differential transmission lines included in the transmission line, wherein the communication circuit receives a notification on a connection status from the external device by at least one of direct current bias potentials of the pair of differential transmission lines; wherein the transmission line is used for bidirectional communication.