Apparatus for selectively measuring ions in a liquid
First Claim
1. Apparatus for selectively measuring ions in a liquid, said apparatus comprising a measuring circuit including a chemically sensitive ion sensor in the form of an ion sensitive field effect transistor (ISFET), a reference electrode, and an amplifier, characterized in that said apparatus includes a protection system for said ISFET comprising a low-impedance contact, a protective element, and at least one electrode connectable to the liquid via said low-impedance contact and coupled to said ISFET by said protective element which has a low impedance to high voltages above the operative voltage range of said ISFET and a high resistance to low voltages below the operative voltage range of said ISFET and which is adapted to become operative outside the operative range of said ISFET.
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Accused Products
Abstract
The apparatus (14) is constructed and arranged to measure ions in a liquid (30) and comprises a measuring circuit (10) including an ISFET (16), a reference electrode (32), an amplifier (22) and a protection system (12)/guard circuit (40) connected to the measuring circuit (10). The protection system 12/guard circuit 40 comprises at least one electrode (46 or 47) connected via a low-impedance contact (or ring 62/46 or ring electrode 42) to the liquid (30) and coupled to the ISFET (16) by a protective element (64; 65, 66; or 68 and/or 50; 51, 52; 54; 56; or 58) having a low-impedance for high voltages and a high resistance to low voltages.
In one preferred embodiment, the ISFET (16) is provided on a chip (90) and has an electrode (46/62) in as closely spaced relationship as possible to the gate region (34) of the ISFET (16).
22 Citations
14 Claims
- 1. Apparatus for selectively measuring ions in a liquid, said apparatus comprising a measuring circuit including a chemically sensitive ion sensor in the form of an ion sensitive field effect transistor (ISFET), a reference electrode, and an amplifier, characterized in that said apparatus includes a protection system for said ISFET comprising a low-impedance contact, a protective element, and at least one electrode connectable to the liquid via said low-impedance contact and coupled to said ISFET by said protective element which has a low impedance to high voltages above the operative voltage range of said ISFET and a high resistance to low voltages below the operative voltage range of said ISFET and which is adapted to become operative outside the operative range of said ISFET.
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12. An IFSET chip characterized by having an exposed protective electrode on the chip closely adjacent to the gate region and by said electrode taking the form of a metallic ring positioned around the gate region of the ISFET.
- 13. An ISFET chip characterized by having an electrode on the chip closely adjacent to the gate region of the ISFET and by said electrode being coupled to said ISFET via a diode and/or MOSFET, arranged on the chip, which are adapted to become conductive outside the operative range of the ISFET.
Specification