ISFET-based measuring device and method for correcting drift
First Claim
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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Accused Products
Abstract
The measuring device (10) comprises an ISFET (12) used as a chemically selective ion sensor, a reference electrode (20) positioned adjacent the ISFET (12), an amplifier (22) coupled to the ISFET and control/correction circuitry (30) coupled to the ISFET (12), to the reference electrode (20) and to the amplifier (22). The control/correction circuitry (30) is operable to maintain the drain-source current IDS of the ISFET (12) at a constant value and to correct drift effects of the ISFET (12) on the basis of the logarithmic equation:
ΔV.sub.p =A 1n(t/t.sub.o +1 )
where:
ΔVp =potential drift
A=scale factor for drift and amplitude
to =time constant defining the dependence on time
t=time during which the sensor is operative in the event of continuous operation.
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Citations
14 Claims
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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 amplitude to =time constant defining the dependence on time t=time during which the sensor is operative in the event of continuous operation. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- (a) for timing, with clock signals, time periods of operation of the device;
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10. A method for correcting drift effects of an ISFET in a measuring device comprising an ISFET used as a chemically selective ion sensor, a reference electrode, an amplifier and control circuit means including a clock signal generator for timing, with clock signals, time periods of operation of the device and for maintaining two of 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, VDS adjusted;
said method including the steps of;
effecting drift correction 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 amplitude to =time constant defining the dependence on time t=time during which the sensor is operative in the event of continuous operation. - View Dependent Claims (11, 12, 13, 14)
- VDS constant, ID S constant, VRS adjusted; and
Specification