Design of Capacitive Sensing Chopper Amplifier Used in Artificial Nose Detection System

In this paper, we present the theoretical background and design procedure of a fully differentiated precision charge amplifier that can be used to detect small capacitive changes in an artificial nose detection system (ANose). We will show that with proper topology and optimization of circuit parameters, we can reduce the noise and offset and thus improve the sensitivity while keeping the power consumption at an acceptable level. Since the rate of capacitive changes due to adsorption/desorption is slow, a well-known technique such as chopping and auto zeroing is used in a new way and described in the paper. The advantages/disadvantages of the proposed techniques are described. A combination of these two techniques in a single topology and new capacitive sensor ports are used to improve the sensitivity of detection. Ideally, a sensitivity of 3 zF/√Hz can be achieved, but it could be slightly worse due to various non-idealities not considered.