A touch panel has a panel capacitor, a first capacitor, and a second capacitor. The panel capacitor and the first capacitor are charged and discharged cyclically according to a first phase signal and a second phase signal, such that an input voltage associated with the panel capacitor and the first capacitor is applied to a control circuit. The control circuit charges and discharges a second capacitor based on the input voltage and a reference voltage to compensate the difference between the input voltage and the reference voltage. The capacitance of the panel capacitor could be calculated based on the frequency of charging and discharging the second capacitor.