Patent ID: 6278283
Filing Date: 2001-08-21
Classification: G01P,G01R

Abstract:
A capacitance detecting circuit comprising:a feedback capacitance component;an operational amplifier having an inverting input terminal and an output terminal, said feedback capacitance component being connected between the inverting input terminal and the output terminal;a capacitance sensor having an electrostatic capacitance that changes in response to an external force applied to the sensor, said capacitance sensor having a charge/discharge terminal, and a reference terminal connected to a reference voltage; andcharge/discharge control means for disconnecting the charge/discharge terminal from the inverting input terminal of said operational amplifier and connecting the charge/discharge terminal of said capacitance sensor to a reference voltage source during a first time period for charging said electrostatic capacitance, and disconnecting the charge/discharge terminal from the reference voltage source and connecting the charge/discharge terminal to the inverting input terminal of said operational amplifier during a second time period, to transfer electric charge from the charge/discharge terminal of said capacitance sensor to the inverting input terminal of said operational amplifier, said operational amplifier converting the electric charge so transferred to a voltage as an output voltage of said capacitance sensor.