A driver circuit configured to drive a display panel to perform a display operation and a touch sensing operation is provided. The driver circuit includes a touch and display driver integration (TDDI) circuit and an external circuit. The TDDI circuit is configured to drive the display panel to perform the display operation and the touch sensing operation during a display period and a touch sensing period, respectively. The TDDI circuit outputs a reference signal. The external circuit is disposed outside of the TDDI circuit. The external circuit is configured to output a first output voltage and a second output voltage on the basis of the reference signal from the TDDI circuit. The first output voltage is larger than the second output voltage.