A first current source supplies a tail current It to a plurality of differential pairs. A pre-driver outputs gate signals to the gates of transistors of the corresponding differential pair. A pre-driver is configured to switch the state between the enable state and the disable state. In the enable state, the pre-driver outputs the gate signals that correspond to the differential signals. In the disable state, the pre-driver outputs the gate signals having levels which instruct the transistors of the corresponding differential pair to switch off.