Development and simulation of a silicon-based pressure sensor with digital output

A silicon-based pressure sensor with digital output has been developed by combining a piezoresistive pressure transducer, a CMOS circuit and a chip containing thin-film poly silicon trimming resistors. Digitalization of the transducer's analogue output signal is achieved by connecting it as input to a double-CMOS-inverter cascade with a poly silicon trimming resistor connected to the first inverter's source. Adjustment of the cascade's detection threshold is performed by laser-trimming of this resistor. Four of these digitizing circuits with different threshold voltages were connected in parallel. Simulation of the developed sensor has been performed with SPICE after implementing a novel simulation technique for piezoresistors. These were modelled by separating the temperature and pressure dependences into independent factors and constructing an equivalent into a SPICE netlist.