BRIDGE-OUTPUT-TO-FREQUENCY CONVERTER FOR SMART THERMAL AIR-FLOW SENSORS

A fully integrated bridge-output-to-frequency converter has been reali zed as signal-conditioning circuitry for a one-chip smart thermal mass -flow sensor. The frequency converter reads out four separate resistor bridges of the air-flow sensor in order to realize high sensitivity a nd directional flow measurement over the full angle range of 360 degre es. The converter selects the sensor bridges individually by means of a microprocessor-controlled analog multiplexer. The flow velocity and direction are also calculated by the microprocessor. The relative meas urement cancels all first-order errors. The center frequency is 10 kHz and the sensitivity 1 Hz/(mu V/V). A bridge-offset of 10 mV/V is allo wed, and the linearity error is 0.1%.