Interface circuit including variable impedance circuit and operating method thereof

An interface circuit comprising:

• a first amplifier configured to receive a first input signal and a second input signal, and to output a first output signal and a second output signal, and comprising an impedance circuit connected to nodes outputting the first output signal and the second output signal;
• a second amplifier configured to receive the first output signal and the second output signal, and to output a third output signal;
• a third amplifier configured to receive the third output signal, and to output a fourth output signal and a fifth output signal;
• a code generator circuit configured to generate a control code to adjust an impedance of the impedance circuit;
• and
• a selection circuit configured to select one of the fourth output signal, the fifth output signal, or an error voltage control signal, and provide the one of the fourth output signal, the fifth output signal, or the error voltage control signal that was selected to the code generator circuit.

An operating method of an interface circuit including a first amplifier configured to receive a first input signal and a second input signal and a second amplifier configured to output a first output signal and a second output signal, the operating method comprising:

• receiving a mode selection signal indicating one of a plurality of operation modes;
• selecting one of the first output signal, the second output signal, or an error voltage control signal according to the one of the plurality of operation modes indicated by the mode selection signal;
• adjusting an impedance connected to an output terminal of the first amplifier based on the one of the first output signal, the second output signal, or the error voltage control signal that was selected;
• and
• generating an output signal of the first amplifier based on the impedance that was adjusted.