US 4,701,253 AGranted

ISFET-based measuring device and method for correcting drift

AssigneeSentron v.o.f.

InventorsHendrikus C. G. Ligtenberg, Jozef G. M. Leuveld

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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 I.sub.DS of the ISFET (12) at a constant value and to correct drift effects of the ISFET (12) on the basis of the logarithmic equation: .DELTA.V.sub.p =A 1n(t/t.sub.o +1 ) where: .DELTA.V.sub.p =potential drift A=scale factor for drift and amplitude t.sub.o =time constant defining the dependence on time t=time during which the sensor is operative in the event of continuous operation.

Claims14

Dependent claims

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 V.sub.DS, I.sub.DS and V.sub.RS, said controlling of the three parameters including:
V.sub.DS constant, I.sub.D S constant, V.sub.RS adjusted;
and V.sub.RS constant, I.sub.DS constant, V.sub.D 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, V.sub.p, on the basis of the logarithmic equation:
.DELTA.Vp=A ln (t/t.sub.o +1)
where:
.DELTA.V.sub.p =potential drift
A=scale factor for drift and amplitude
t.sub.o =time constant defining the dependence on time
t=time during which the sensor is operative in the event of continuous operation.

8 more elements

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 V.sub.DS, I.sub.DS and V.sub.RS, said controlling of the three parameters including:

V.sub.DS constant, I.sub.D S constant, V.sub.RS adjusted;
and V.sub.RS constant, I.sub.DS constant, V.sub.DS 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, V.sub.p, on the basis of the logarithmic equation:
.DELTA.Vp=A ln (t/t.sub.o +1)
where:
.DELTA.V.sub.p =potential drift
A=scale factor for drift and amplitude
t.sub.o =time constant defining the dependence on time
t=time during which the sensor is operative in the event of continuous operation.

7 more elements

Dependencies are inferred from the claim text.