CMOS chopper amplifier for chemical sensor

Abstract

A highly sensitive CMOS chopper amplifier used for an oxygen probe is described. It is integrated in a 2- mu m double-poly p-well CMOS process. The chip uses only a single 5-V voltage source, and no external components are needed. It is realized by a current mode chopper technique in order to overcome the low-frequency noise and drift problems. The clock feedthrough generated by the chopper circuit is reduced by using a switched-capacitor-filter technique. The switched-capacitor technique is also used to implement the function of demodulation. The simulated current is converted into an output voltage with a slope of approximately 100 mV/nA. The current signal from 0.2 to 8 nA can be measured with a nonlinearity of 3.5%. Experimental results are given showing the performance of this amplifier.< >