US Patent 8164555 Display device including driver circuit and monitor circuit

To provide a display device which can ensure high reliability of a driver circuit even when a threshold voltage of a TFT shifts. The display device includes a power supply control circuit which can apply a forward bias voltage or a reverse bias voltage to a gate of a transistor included in an output circuit, a monitor transistor which is formed to monitor the amount of change of a threshold voltage of the transistor included in the output circuit, and a threshold control circuit which controls the power supply control circuit so as to apply the reverse bias voltage to the gate of the transistor in order to compensate the threshold voltage of the transistor included in the output circuit.