PHASE SHIFT DETECTION AND MEASUREMENT CIRCUIT FOR CAPACITIVE SENSOR

摘要

A capacitor measurement and detection circuit (8) for monitoring changes in a sensor capacitor, comprising: a bridge circuit (20) including a reference capacitor (400) and the sensor capacitor (100) for generating output signals (510, 520) indicative of the difference between the magnitude of the reference and sensor capacitors; a fixed frequency oscillator (10) connected to the bridge circuit for driving the bridge circuit at a fixed frequency; a bridge imbalance detector (30) responsive to the output of the bridge circuit for generating conditioned signals; a counter driven by the oscillator (10) and responsive to the output signals of the detector (30) for generating an output signal indicative of the phase difference between the reference arm of the bridge circuit and the active arm of the bridge circuit, thereby providing an indication that an object is positioned in the electric field created by the sensor (50).