A controller adapted to an in-cell touch screen includes a common voltage (VCOM) circuit generating a common voltage at an output node of the VCOM circuit, and a detecting circuit receiving a sensing signal at an input/output node of the detecting circuit. A display-mode switch is closed in a display mode such that a VCOM electrode is set at the common voltage, and a touch-sensing-mode switch is closed in a touch sensing mode such that the sensing signal from the VCOM electrode is received and processed by the detecting circuit. The detecting circuit has full-swing power that contains full-swing power of the VCOM circuit.