Hall cell geartooth sensor with 15 gauss sensitivity

A monolithic sensor for detecting time-varying magnetic fields, which combines precision analog circuits with a Hall cell, is described. The device withstands the rigorous environment of an automobile engine ignition control system where it detects teeth on a rotating ferrous wheel. The open-collector digital output responds to field changes of 15+or-1 G over a -55 degrees C to 150 degrees C range. Yield is improved by laser trim of silicon chromium resistors, eliminating the process dependence of Hall cell sensitivity. An AC-coupling scheme using an external 1- mu F capacitor rejects system offsets of several hundred G while allowing full sensitivity with signals as slow as 4 Hz. Other features include controlled startup and shutdown behavior and insensitivity to system noise. The 110-transistor. 10.700-mil/sup 2/ device is packaged in a 4-pin SIP, and operates on a single 5- to 16-V supply.<
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