An interface circuit includes: a buffer circuit configured to receive an input signal and to generate an output signal having a delay time, the delay time being determined based on a current level of a bias current and a voltage level of a power supply voltage; and a bias generation circuit configured to vary a voltage level of a bias control voltage so that the delay time is constant by compensating for a change in the voltage level of the power supply voltage, the bias generation circuit being further configured to provide the bias control voltage to the buffer circuit.