Circuit provides constant current for ISFETs/MEMFETs

摘要

ISFETS and MEMFETS (ion-sensitive and membrane FETs) are sol- id-state chemical sensors that provide an electrical signal associated with the change of a chemical concentration in a solution. These types of sensors need a stable operating point. A common operating point is a drain-source current of 100A and a drain-source voltage of 500 mV. Under these conditions, the sensed chemical information is contained in the gate-source voltage. Figure 1 shows a constant-current driver for ISFETs/MEMFETs. The current source, I, produces a voltage drop in resistor R_1:the voltage follower reflects this voltage to the drain-source terminals of the chemical sensor.