A driving circuit includes: a first reference current source injects a reference current; each first switch unit is coupled between the first reference current source and one of first and second output ports; a second reference current source sinks the reference current; each second switch unit is coupled between the second reference current source and one of the output ports; a load unit is coupled between the output ports, and a common voltage is applied onto the load unit; and a calibration module calibrates an impedance of the load unit according to a voltage at one of the output ports, and the voltage is generated due to the reference current passing through one of the first switch units, the load unit, and one of the second switch units.