The conventional ion senwtlve sensors, such as glass membrane electrodes,
coated unre electrodes, metal-metal oxide electrodes, etc , convert a
non-electrical quantity mto an electrical quantity, which can then be
measured wrth approplnate electronic clrcultry connected m senes Unpredictable
devlatlons m transducer parameters cannot be controlled m such
a measunng system Because the ISFET also has an electrical mput besides
the ion-senatlve input, this results m unique apphcatlon posslbllltles, mth
consequences for the development of adequate electromc clrcultry In order
to obtzun an insight mto this matter, It 1s useful first to understand the electmcal
behavlour of a MOSFET, from which the ISFET behavlow can be
denved. Based on this theory some electromc design startmg points can be
developed for an appropnate ISFET apphcatlon