An opto-electronic 18 b/revolution absolute angle and torque sensor for automotive steering applications

This application-specific integrated circuit (ASIC) computes two optically encoded positions, each engraved in a pattern onto one of a two-cylinder assembly. The cylinders are coupled by a torsion bar of known stiffness so that the difference between the two extracted positions provides a torque measurement to be used in next-generation automobile electrical power assisted steering (EPAS) systems. The cylinder positions are defined by 11b absolute-position encoders plus 7 additional bits of interpolated (relative) position between adjacent codes. The circuit is controlled and accessed via a serial peripheral interface (SPI).