Patent ID: 7119550

Claim:
A capacitance difference detecting circuit comprising: a pair of oscillators having capacitors whose capacitances change according to an external force and generating first oscillating signals according to the capacitances, respectively; a detecting unit detecting a relative difference between the capacitances as a difference between frequencies of the first oscillating signals; a mask control unit that activates a mask signal when the difference between the frequencies of the pair of first oscillating signals is smaller than a preset value, wherein said detecting unit includes a mixer receiving a pair of first oscillating signals and outputting a frequency difference signal with a frequency equal to a difference between frequencies of the received pair of first oscillating signals, and a frequency/voltage converting unit that converts the frequency of the frequency differences signal to a detection voltage indicating the relative difference between the capacitances and while receiving the activated mask signal, said frequency/voltage converting unit outputs the detection voltage indicating that the difference between the capacitances is zero.