Patent ID: 6710606
Filing Date: 2004-03-23
Classification: A47K,B65H,H03K,Y10T

Abstract:
A proximity sensor circuit, comprising:an antenna having a baseline stray capacitance; an oscillator circuit coupled to the antenna and generating an oscillation signal having a predetermined oscillation amplitude corresponding to the baseline stray capacitance of the antenna, the oscillation amplitude of the oscillation signal increasing in response to an increase in stray capacitance from the baseline stray capacitance of the antenna and decreasing in response to a decrease in stray capacitance from the baseline stray capacitance of the antenna; and an automatic sensitivity control circuit coupled to the oscillator circuit and detecting a change in the oscillation amplitude of the oscillator signal, the automatic sensitivity control circuit controlling the amplitude of the oscillator signal to counteract a change in stray capacitance from the baseline stray capacitance of the antenna and maintaining the oscillation amplitude of the oscillator signal at the predetermined oscillation amplitude to provide a substantially constant sensitivity to changes in stray capacitance from the baseline stray capacitance of the antenna.