Ultra-small capacitance sensing circuit based on a piece of ASIC

A circuit based on a piece of Applications Specific Integrated Circuit (ASIC) HT133 for sensing ultra-small capacitance is presented. It has some prominent features such as high resolution, high anti-interference ability, offset adjustment ability and both analog and digital signal output modes. Implementation of every module and means of noise limitation are described detailedly. An experiment measurement of a series of small capacitances is performed. Results show that the circuit has very high performance with resolution of 0.5 femtofarad (0.5 × 10^-15 farad) and nonlinearity of 8.67%. A basis for this ASIC to be applied in capacitive sensors especially micro-electro-mechanical system (MEMS) sensors is provided.