An input buffer includes a first amplification block, a second amplification block, and a buffer block. The first amplification block is configured to be driven by an external voltage, to differentially amplify an input signal and a reference voltage in response to a bias voltage, and to subsequently generate first and second differential signals. The second amplification block is configured to be driven by an internal voltage, to differentially amplify the first and second differential signals, and to generate an output signal. The buffer block is configured to be driven by the internal voltage, to buffer the output signal, and to output an inverted output signal.