Patent ID: 6928173
Filing Date: 2005-08-09
Classification: H04R

Abstract:
1. A capacitor microphone comprises a microphone unit varying capacitance in response to inputted sound pressure, a first oscillator, a second oscillator, a phase synchronous means, a clock pulse oscillator generating clock pulses, a first logical product circuit, a second logical product circuit and a adder-subtracter, wherein said first oscillator outputs a sound signal of which frequency varies in response to the capacitance and said second oscillator outputs a tracking signal of which frequency varies in response to a control voltage, wherein said phase synchronous means obtains the sound signal and the tracking signal, and outputs the first control signal when the phase of the sound signal leads the phase of the tracking signal, while the phase synchronous means outputs the second control signal when the phase of the sound signal lags behind the phase of the tracking signal, so that the control voltage is controlled in order that both phases of the sound signal and tracking signal become equal, wherein said first logical product circuit outputs an adding-pulse signal generated by the logical product of the first control signal and the clock pulses, and said second logical product circuit outputs a subtracting-pulse signal generated by the logical product of the second control signal and the clock pulses, wherein said adder-subtracter outputs digital sound data by counting the adding-pulse signal and the subtracting-pulse signal.