Sensitivity enhancement of P- and N-MOS based current mirror pressure sensor using differential amplifier.

The aim of this work is to enhance the full scale output voltage and sensitivity of a PMOS based current-mirror integrated pressure sensor. A source coupled differential amplifier has been designed using PMOS transistors and implemented to achieve the same. The proposed sensing structure includes three p-channel MOSFETS connected in current-mirror configuration followed by two p-channel MOSFETS in common source differential amplifier configuration. Transistor M1 (reference transistor) of the mirror circuit serves as constant current source while transistor M2 and transistor M3, integrated on the flexible membrane, are active transistors for sensing pressure. When the sensing membrane is subjected to external pressure, M2 and M3 sense the maximum tensile and compressive stresses respectively. The piezoresistive nature of these MOSFETs allows for the computation of stress- induced variation in hole mobility within the channel of active MOSFETM2 and MOSFET M3. The differential amplifier is made up of the two PMOS transistors M4 and M5 on the same chip. The complete structure is designed in TSpice software using the 5 µm CMOS technology parameters. It amplifies the output voltage from the current-mirror sensing circuit to give enhanced pressure sensitivity. Employing this arrangement, an improvement in pressure sensitivity from 467.4 to 972.5 mV/MPa is achieved. Comparison with the previously reported n-channel MOSFET counterpart shows that NMOS devices exhibit better sensitivity. [ABSTRACT FROM AUTHOR]