A multi-element monolithic mass flowmeter with on-chip CMOS readout electronics

The implementation of control circuitry is presented for a multielement mass flow sensor capable of simultaneously measuring five different gas-related parameters necessary for mass flow. A process has been developed to merge the micromachined sensing structures and the CMOS readout circuitry on a single chip. The total process requires thirteen masks: eight for the double-poly, single-metal CMOS process and five for additional processing of the transducer elements. The on-chip circuitry includes offset-free instrumentation amplifiers, an analog multiplexer, heater drive circuits, self-test circuitry, and a bandgap temperature sensor using substrate n-p-n bipolar transistors. The resulting multielement chip requires only ten external pins and delivers high-level buffered output signals describing gas velocity, type, direction, pressure, and temperature.