ISFET amplifier analysis with HSPICE

Analysis of three ISFET amplifiers with HPSICE is presented. The three circ uits maintain drain current and drain to source voltage constant but they d iffer in complexity. ISFET modeling has been performed with the SPICE level 2 MOS model and having the same geometry as the ISFETs manufactured at CNM . The obtained Id-Vg characteristics of the real and simulated device are v ery similar. In order to analyse the circuit behaviour, we have simulated t heir response to a pH step and to a reference electrode disconnection. By t his method the stability of different designs and the capability to work in flux systems can be obtained. Results showed that the simplest circuit has the best features.