Patent ID: 7119551

Claim:
An improved two loop capacitive sensor oscillator circuit to convert a transducer capacitance to frequency comprising: a first loop to create an oscillatory waveform having a frequency related to a capacitance of the capacitive transducer, the first loop including a resistor having a resistor first connection and a resistor second connection, the resistor second connection electrically coupled to a capacitor (Cs 1 ), having a capacitor (Cs 1 ) first connection and a capacitor (Cs 1 ) second connection, the resistor second connection electrically coupled to the capacitor (Cs 1 ) first connection and the capacitor (Cs 1 ) second connection electrically coupled to an electrical common, the resistor second connection also electrically coupled to the capacitive transducer, the capacitive transducer having a capacitive transducer first connection and a capacitive transducer second connection, the resistor second connection electrically coupled to the capacitive transducer first connection, the capacitive transducer second connection electrically coupled to an input of a first inverter gate also having a first inverter gate output, the first inverter gate output electrically coupled to a second inverter gate input, the second inverter gate also having a second inverter gate output, and the second inverter gate output electrically coupled to the resistor first connection, closing the first loop, the first and second inverter gates powered by a source of power (Vcc); and a second loop oscillating at the frequency of the first loop and to further generate a second waveform of a substantially square wave shape having the same frequency, the second loop electrically coupled to the first loop, the second loop including an input to the second loop being the input of a third inverter gate also having a third inverter gate output, the third inverter gate input electrically coupled to the second inverter gate output, the third inverter gate output electrically coupled to a second loop resistor first connection, the second loop resistor also having a second loop resistor second connection, the second loop resistor second connection electrically coupled to the input of the first inverter gate, closing the second loop, the third inverter gate also powered by the source of power (Vcc), wherein the second loop is electrically coupled to the first loop and the output of the third inverter gate is the substantially square wave at the frequency related to the capacitance of the capacitive transducer.