LOW NOISE SIGNAL PROCESSING FOR MEMS/NEMS BASED CHEMICAL/BIOLOGICAL SENSORS: A SYSTEM PERSPECTIVE

The paper presents architecture, design, modeling and implementation of low-noise signal processing electronics needed to implement high-resolution MEMS/NEMS based capacitive sensors interfaces, which can be used for chemical/biological sensor interface. Using double-mixing lock-in amplifier principle with signal processing appropriately distributed between analogue and digital circuitry, using low noise charge amplifier, low-noise programmable gain stage, several low-noise filters, 2nd order XA modulator and the DSP a very high SnR is achieved. With proposed architecture, it is possible to sense a capacitance difference smaller than 0.5aF//Hz on a 2pF feedback capacitors with SnR (1Hz) better than 134dB. Because of achieved characteristics it is possible to use proposed interface for sensing capacitance changes of micro/nano scale based chemical and/or biological sensors with ultimate sensitivity. The circuitry is implemented in 0.350pm BCD technology and occupies approx. 2.5 mm2. Using this electronics together with chemically modified MEMS COMB capacitive sensor the measured detection level is better than 5ppb vapor molecules in the air at room temperature.