Capacitance sensing circuit

A capacitance sensing circuit for sensing a detection capacitor of a detecting circuit, wherein, the detecting circuit receives an input signal and generates an output signal, the capacitance sensing circuit comprises:

• a capacitance judging circuit coupled to the detecting circuit and configured to judge a capacitance of the detection capacitor according to the output signal;
• and
• an input signal generator coupled to the detecting circuit and configured to generate the input signal according to noise, the input signal generator comprises:
• a phase detection unit configured to receive the noise and detect a first phase of the noise;
• a phase calculation unit coupled to the phase detection unit and configured to receive the noise and the first phase, and calculate an optimum phase according to the noise or the first phase;
• and
• a first waveform generator coupled to the phase calculation unit, and configured to generate the input signal according to the optimum phase-, wherein the first waveform generator converts the optimum phase into a delay time, and there is a time difference between the input signal and a parent signal, the time difference is the delay time.