Position Detection in Automotive Application by Adaptive Inter Symbol Interference Removal

Incremental magnetic field sensors are frequently used in automotive applications for crankshaft and camshaft position measurements. Highest possible phase accuracy and disturbance immunity (air gap and temperature variations, noise) are the primary performance requirements for such sensor systems. An analog signal is generated from a magnetic field sensor and the position information is obtained using state of the art peak or zero crossing detection in the analogue or digital domain. While phase jitter of peak or zero crossings can be minimized by optimizing zero crossing and peak detection methods, these techniques cannot take into account variations of peak and zero crossing positions due to air gap variations. A Decision Feedback Equalizer (DFE) was adapted to remove this systematic error. For this purpose a physical model of the measurement environment (magnetic field) was derived and verified by Finite Element simulations (FEM). With simplifications the model delivered an analytical function for magnetic field calculations, which serve the adaptive algorithm for the DFE.