Abstract: This paper presents a high precision CMOS opamp suitable for ISFET readout.The opamp is tailored to provide a constant bias condition for ISFET as part of the readout circuits and,hence,is compatible for single chip integration with the sensor.A continuous time auto-zero stabilization technique is studied and employed,with the aim of suppressing the low frequency noises,including the offset voltage,1/f noise,and temperature drift.The design is based on a 0.35μm CMOS process.With a 3.3V power supply,it maintains a DC open loop gain of more than 100dB and an offset voltage of around 11μV,while the overall power dissipation is only 1.48mW.With this opamp,a pH microsensor is constructed,of which the functionality is verified by experimental tests.

Key words: high precision, auto-zero, operational amplifier, ISFET microsensor