Patent ID: 7944217

Claim:
An object proximity detector, consisting of a sensor plate connected to a sensor oscillator, sensing proximity of an object by the variation of the capacitance; a sensor oscillator, the variation of the capacitance changes the frequency of said sensor oscillator, the output of said sensor oscillator is connected to the input of a counter; a counter, counting the frequency of said sensor oscillator, the output of said counter is communicated with a microprocessor; a time base oscillator, providing system clock to a microprocessor; a microprocessor, counting and processing the frequency count from said counter to determine that an object is in proximity of said object proximity detector; wherein the improvement comprising: said sensor oscillator consists of three inverters, a first inverter, a second inverter and a third inverter are in cascaded; a first capacitor is connected between the input of said first inverter and the ground; two capacitors in series are connected between the input of said first inverter and the output of said third inverter; a sensor plate connected at the junction of said two capacitors; a compensating capacitor connected between the input of said first inverter and the output of said second inverter; a feedback resistor connected between the input of said first inverter and the output of said third inverter; said feedback resistor is used to charge and discharge said capacitors in the oscillator circuit, said compensating capacitor is used to reduce the dependence of oscillator frequency on the process parameters, said two capacitors in series and said sensor plate is used to reduce the dependence of oscillator frequency on the area of sensor plate and to keep the flexibility of the connecting wire of said sensor plate.