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ISFET-based measuring device and method for correcting drift

  • US 4,701,253 A
  • Filed: 10/29/1984
  • Issued: 10/20/1987
  • Est. Priority Date: 11/03/1983
  • Status: Expired due to Fees
First Claim
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1. A measuring device comprising an ISFET having a drain and a source used as a chemically selective ion sensor, a reference electrode positioned adjacent said ISFET, an amplifier coupled to said ISFET, control circuit means including a clock signal generator coupled to said ISFET, to said reference electrode and to said amplifier:

  • (a) for timing, with clock signals, time periods of operation of the device;

    (b) for maintaining two of the three operating parameters of said ISFET constant while adjusting the third parameter, the parameters being VDS, IDS and VRS, said controlling of the three parameters including;

    VDS constant, ID S constant, VRS adjusted; and

    VRS constant, IDS constant, VD S adjusted; and

    (c) for effecting correction of drift, due to drift effects of said ISFET including adjusting the voltage supplied to the reference electrode relative to changes in potential drift, Vp, on the basis of the logarithmic equation;

    
    
    space="preserve" listing-type="equation">Δ

    Vp=A ln (t/t.sub.o +1)where;

    Δ

    Vp =potential driftA=scale factor for drift and amplitudeto =time constant defining the dependence on timet=time during which the sensor is operative in the event of continuous operation.

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