A smart bipolar thermal flow sensor with frequency output

A smart two-dimensional flow sensor with frequency output is presented. The sensor measures flow-induced on-chip temperature differences to determine both direction and intensity of the flow. The temperature differences are on-chip converted to two TTL (transistor transistor logic) compatible frequency-modulated output voltages in the range of 5 to 15 kHz, from which both flow intensity and direction can be calculated. An etched groove provides a thermal isolation between the measurement and the signal processing part of the chip. The small dimensions of the sensor (6*6 mm/sup 2/) and the fact that a standard IC process is used to make this sensor suitable for both industrial and consumer products. A digital output signal can be obtained by using a minimum of external components.<>