A chopped Hall sensor with small jitter and programmable "True Power-on" function

Abstract

A chopped Hall sensor for camshaft applications is presented which provides a programmable "True Power-on" switching level effective after the power-up phase. The proposed chopping technique and self-compensation methods for temperature drift and technology spread provide a correct output state immediately after power-on even at zero speed of the target wheel. The circuits improve the magnetic offsets from 5 to 10 mT to below 200 /spl mu/T in a bandwidth of 30 kHz and stabilize the spread of the magnetic switching points from 20% to <2% in a temperature range from -40/spl deg/C to 175/spl deg/C. The novel combination of chopping and enhanced digital self-calibration algorithm adjusts the magnetic switching point and improves phase accuracy to <0.5/spl deg/, independent of air gap variations between sensor and wheel. An end-of-line calibration for the customer is implemented using surface micromachined cavity fuses which offer a reliable function higher than 195/spl deg/C.