Design of an on chip read-out circuit for piezo-resistive MEMS pressure sensor

The proposed read-out circuit has a traditional two stage Operational amplifier (op-amp), a Gilbert cell and a Difference amplifier. The sensitivity of the sensor, known as primary with pressure variation can be increased with the help of an additional sensor, which act as a reference sensor. Here, we have used a current bias to increase the sensitivity. The current through both the sensors are controlled by a composite resistor and an op-amp having 70db PSRR. The advantage of using composite resistor is its immunity to process variation as well as stabilization of current sourced into the sensors. The simulation of the sensor along with the read out bias circuit is performed in cadence environment with AMS (Austria Microsystems) 0.35 μm technology design kit. The simulation for in-house fabricated MEMS pressure sensor is done by macro-modeling. The simulated output of the read-out circuit along with the macro model of sensor is showing almost rail-to rail output swing (around 3 V for a 3.3 V supply). The total power dissipation (including the sensor) is less than 10 mW for a 3 mA bias current. The total area occupied by the readout circuit is less than 0.04 mm2. MEMS pressure sensor was fabricated by SNG group of CEERI, fabricated sensor occupies 0.14 mm2 of area.