Analysis of a Linearizing Direct Digitizer With Phase-Error Compensation for TMR Angular Position Sensor

This paper proposes an efficient linearizing direct digitizer for tunneling magnetoresistance (TMR)-based angular position sensor. The proposed linearizing digitizer for TMR angle sensors (LDTA) converts sine and cosine natured analog outputs from the TMR sensor into a digital output that varies linearly over 360° range. The digitization is done without using any analog-to-digital converter. The novel methodology of the LDTA ensures that its performance is least affected by the phase error of the quadratic oscillator used for sensor excitation. This principle also prohibits the adverse effects of the parasitic capacitances of the TMR sensor on angle measurement. Error sources influencing the LDTA performance are identified and analyzed. Detailed simulation and emulation studies of the LDTA were conducted to confirm its methodology. The worst case nonlinearity spotted during emulation studies remains within 0.08% for various probable values of phase error. A TMR-based angle sensor unit is designed and built. Interfacing the LDTA with the developed sensor unit gives an output with worst case nonlinearity of 0.28% and minimal phase-error dependence. The performance of the LDTA is tested and quantified for various other scenarios, including dynamic input conditions and sensor-unit imperfections. The superior performance of the LDTA to that of the existing techniques is also revealed in this paper.