Digitizing ohmmeter system
First Claim
1. A method for sampling and digitizing a resistance measurement from an impedance-varying input sensor, comprising:
- applying a switched excitation source to said input sensor;
generating an input voltage step at said input sensor as a result of said application of said switched excitation source, said input voltage step being indicative of the resistance of said input sensor;
AC coupling said input voltage step to an integrator;
integrating charges corresponding to a transition of said input voltage step on an accumulation capacitor;
generating a fullscale resistance reference signal;
applying said fullscale resistance reference signal to said integrator;
generating a data dependent signal for deactivating or activating said integrator;
integrating a reference charge packet associated with a transition of said fullscale resistance reference signal when said data dependent signal has a first value or disregarding said reference charge packet when said data dependent signal has a second value, said transition of said fullscale resistance reference signal being opposite to said transition of said input voltage step;
comparing a signal corresponding to said charges accumulated on said accumulation capacitor with a reference level; and
generating an output signal as a result of said comparing, said data dependent signal having said first value and said second value corresponding to respective logical levels of said output signal,wherein after a plurality of sampling cycles, said output signal forms a digital data stream having an ones density proportional to a ratio of the resistance of said input sensor to said fullscale resistance reference signal.
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Abstract
A digitizing ohmmeter system for providing a digital resistance measurement includes a current source for providing an excitation current to an impedance-varying input sensor and an ADC circuit including a charge-balancing modulator and a digital post processing circuit. The system utilizes synchronous AC excitation of the input sensor and an AC coupled analog-to-digital converter input. The digitizing ohmmeter system also implements correlated double sampling for noise cancellation to provide low noise and highly accurate analog-to-digital conversions. The ADC circuit includes a reference signal generator generating a resistance reference signal by time-sharing the excitation current with the input sensor. The digitizing ohmmeter system thereby realizes fully ratiometric operation such that neither a precise current source nor a precise voltage source is required for accurate resistance measurements.
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Citations
10 Claims
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1. A method for sampling and digitizing a resistance measurement from an impedance-varying input sensor, comprising:
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applying a switched excitation source to said input sensor; generating an input voltage step at said input sensor as a result of said application of said switched excitation source, said input voltage step being indicative of the resistance of said input sensor; AC coupling said input voltage step to an integrator; integrating charges corresponding to a transition of said input voltage step on an accumulation capacitor; generating a fullscale resistance reference signal; applying said fullscale resistance reference signal to said integrator; generating a data dependent signal for deactivating or activating said integrator; integrating a reference charge packet associated with a transition of said fullscale resistance reference signal when said data dependent signal has a first value or disregarding said reference charge packet when said data dependent signal has a second value, said transition of said fullscale resistance reference signal being opposite to said transition of said input voltage step; comparing a signal corresponding to said charges accumulated on said accumulation capacitor with a reference level; and generating an output signal as a result of said comparing, said data dependent signal having said first value and said second value corresponding to respective logical levels of said output signal, wherein after a plurality of sampling cycles, said output signal forms a digital data stream having an ones density proportional to a ratio of the resistance of said input sensor to said fullscale resistance reference signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification