Circuit for measuring ion concentrations in solutions

US5602467A · kind A · utility

Assignee

• Fraunhofer-Gesellschaft zur förderung der angewandten Forschung e.V. · DE

Inventors

• Mathias Krauss · Centerport, US
• Beate Hildebrandt · Muchow, DE
• Christian Kunath · Dresden, DE
• Eberhard Kurth · Radebeul, DE

Key dates

• Filing date: Apr 24, 1995
• Grant date: Feb 11, 1997
• Expiry date: Apr 24, 2015

Classification

• Technology area (CPC G): Physics
• CPC primary: G01N27/4148
• WIPO field: Measurement
• WIPO sector: Instruments

Abstract

A circuit layout for measuring ion concentrations in solutions using ion-sitive field effect transistors is provided. The circuit layout makes it possible to represent the threshold voltage difference of two ISFETs directly and independently of technological tolerances, operationally caused parameter fluctuations, and ambient influences. The circuit layout includes two measuring or test amplifiers, with in each case two differently or identically sensitive ISFETs and two identical FETs. The ISFETs and FETs are connected in such a manner that at the output of the first measuring amplifier occurs the difference of the mean value of the two ISFET threshold voltages and the FET threshold voltage and at the output of the second measuring amplifier occurs the difference of the two ISFET threshold voltages. The output of the first amplifier is connected to the common reference electrode of the four ISFETs.