Patent ID: 6975103

Claim:
A digitizing ohmmeter system for measuring the ratio of the resistance of an impedance-varying input sensor to a reference resistance, comprising: a high impedance current source providing a DC excitation current to a reference resistor and said input sensor, said reference resistor and said input sensor being connected in series between a first node receiving the DC excitation current and a second node; and an analog-to-digital converter (ADC) circuit for providing a resistance output signal comprising: a switched capacitor input stage for sampling a voltage across said reference resistor and a voltage across said input sensor to generate a switched reference voltage step indicative of the resistance of said reference resistor and a switched input voltage step indicative of the resistance of said input sensor; a modulator coupled to integrate charge associated with said input voltage step and balance said charge with charge associated with said reference voltage step, said modulator generating a digital output signal, said digital output signal forming a digital data stream over a plurality of sampling cycles where said digital data stream has an ones density proportional to the ratio of the resistance of said input sensor to the resistance of said reference resistor; and post processing circuit coupled to receive said digital data stream and generating a digital number indicative of the occurrence of ones in said digital data stream within said plurality of sampling cycles as said resistance output signal.