CONTROL SYSTEM WITH CAPACITIVE DETECTOR

摘要

A capacitive sensor system for controlling operation of a device in response to a rate of change in capacitance due to motion of a proximate object includes at least two sense electrodes (14,16) disposed on a surface and a phase locked loop (12), including a voltage controlled oscillator (22) and a phase/frequency comparator (24), connected between the sense electrodes and an RC network (20) for providing an operating frequency to the sense electrodes. A circuit loop, including a reference oscillator (32), provides a fixed frequency references for the phase locked loop to follow and a phase delay circuit (34) connected between the phase/frequency comparator and the voltage controlled oscillator causes the voltage controlled oscillation to run ahead of the reference oscillator. A trigger circuit (30) provides a control output in response to a change in phase shift between the fixed frequency and the operating frequency.