Apparatus and method for operating an ISFET at multiple drain currents and gate-source voltages allowing for diagnostics and control of isopotential points
First Claim
1. An apparatus for measuring ion concentration of a solution, comprising;
- an ion sensitive field effect transistor (ISFET) having a drain, a source, an ion sensitive gate region and a plurality of device characteristics;
a reference device separated from the gate region;
an ISFET control circuit coupled to the ISFET which operates the ISFET at a drain-source voltage VDS and at n successive drain currents IDi and corresponding gate-source voltages VGSi such that the ISFET has an isopotential ion concentration point which is different for each of the n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer variable from 1 to n and n is an integer greater than 1;
a memory which stores the plurality of device characteristics and the n successive drain currents IDi and gate-source voltages VGSi ;
measurement means for measuring ion concentration of the solution as a function of at least one of the n successive drain currents IDi and gate-source voltages VGSi and the plurality of device characteristics stored in the memory; and
diagnostic means for measuring at least one of the device characteristics of the ISFET as a function of the n successive drain currents IDi and gate-source voltages VGSi.
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Accused Products
Abstract
An apparatus for measuring ion concentration of a solution includes an ion sensitive field effect transistor (ISFET), a reference device, an ISFET control circuit, a memory, a measurement circuit and a diagnostic circuit. The ISFET has a drain, a source, an ion sensitive gate region and a plurality of device characteristics. The reference device is separated from the gate region by a sample solution. The ISFET control circuit is coupled to the ISFET and operates the ISFET at a drain-source voltage VDS and at n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer from 1 to n and n is an integer greater than 1. The memory stores the plurality of device characteristics and the n successive drain currents IDi and gate-source voltages VGSi. The measurement circuit measures ion concentration of the solution as a function of at least one of the n successive drain currents IDi and gate-source voltages VGSi and the plurality of device characteristics stored in the memory. The diagnostic circuit measures at least one of the device characteristics of the ISFET as a function of the n successive drain currents IDi and gate-source voltages VGSi.
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Citations
20 Claims
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1. An apparatus for measuring ion concentration of a solution, comprising;
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an ion sensitive field effect transistor (ISFET) having a drain, a source, an ion sensitive gate region and a plurality of device characteristics; a reference device separated from the gate region; an ISFET control circuit coupled to the ISFET which operates the ISFET at a drain-source voltage VDS and at n successive drain currents IDi and corresponding gate-source voltages VGSi such that the ISFET has an isopotential ion concentration point which is different for each of the n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer variable from 1 to n and n is an integer greater than 1; a memory which stores the plurality of device characteristics and the n successive drain currents IDi and gate-source voltages VGSi ; measurement means for measuring ion concentration of the solution as a function of at least one of the n successive drain currents IDi and gate-source voltages VGSi and the plurality of device characteristics stored in the memory; and diagnostic means for measuring at least one of the device characteristics of the ISFET as a function of the n successive drain currents IDi and gate-source voltages VGSi. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An apparatus for measuring ion concentration of a solution, comprising:
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an ion sensitive field effect transistor (ISFET) having a drain, a source and an ion sensitive gate region; a reference device separated from the gate region; an ISFET control circuit coupled to the ISFET for applying a drain-source voltage VDS across the drain and source and for operating the ISFET at n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer variable from 1 to n and n is an integer greater than 1, wherein the drain currents flow through the drain of the ISFET and the gate-source voltages are referenced between the reference device and the source, and wherein the ISFET has an iso potential ion concentration point which is different for each of the n successive drain currents IDi and corresponding gate-source voltages VGSi ; a memory which stores the n successive drain currents IDi and gate-source voltages VGSi ; and measurement means for making n successive ion concentration measurements of the solution as a function the n successive drain currents IDi and gate-source voltages VGSi and for providing an ion concentration output based on an average of the n successive ion concentration measurements.
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16. A method of measuring ion concentration of a solution with an apparatus comprising a reference device and an ion sensitive field effect transistor (ISFET) having a drain, a source, an ion sensitive gate region and a plurality of device characteristics, wherein the ion sensitive gate region and the reference device are exposed to and separated by the solution, the method comprising:
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applying a drain-source voltage VDS across the drain and source; operating the ISFET at n successive drain currents IDi and corresponding gate-source voltages VGSi such that the ISFET has an isopotential ion concentration point which is different for each of the n successive drain currents IDi and corresponding gate-source voltages VGSi, wherein i is an integer variable from 1 to n and n is an integer greater than 1, and wherein the drain currents flow through the drain of the ISFET and the gate-source voltages are referenced between the reference device and the source; storing the plurality of device characteristics and the n successive drain currents IDi and gate-source voltages VGSi ; measuring ion concentration of the solution as a function of at least one of the n successive drain currents IDi and gate-source voltages VGSi and the stored device characteristics; and measuring at least one of the device characteristics of the ISFET as a function of the n successive drain currents IDi and gate-source voltages VGSi. - View Dependent Claims (17, 18, 19, 20)
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Specification