Patent ID: 8089290

Claim:
A measurement circuit for providing a voltage output from a resistance sensor, said measurement circuit comprising: a resistance-to-frequency conversion circuit electrically coupled to the sensor and providing an AC excitation signal to the sensor, said resistance-to-frequency conversion circuit being responsive to a resistance signal from the sensor that is to be measured, said resistance-to-frequency conversion circuit including an oscillator amplifier having a first input coupled to the sensor and an output coupled to the sensor, said oscillation amplifier generating a sinusoidal frequency signal having a frequency that changes based on the resistance of the resistance signal, said resistance-to-frequency conversion circuit further including a comparator amplifier having a first input coupled to the output of the oscillator amplifier, a second input coupled to a second input of the oscillator amplifier and an output coupled to the first input of the oscillator amplifier, said comparator amplifier being a feedback amplifier that converts the sinusoidal frequency signal from the oscillator amplifier to a square wave signal of the same frequency and causes the oscillator amplifier to be a self-oscillating circuit to provide the AC excitation signal to the sensor; and a frequency-to-voltage conversion circuit responsive to the square wave signal from the comparator oscillator, said frequency-to-voltage conversion circuit converting the frequency signal to a representative voltage signal.