Analysis of a Faster Digitizer for Tunneling Magneto-Resistance Angle Sensor Configured in Push-Pull Natured Two Half-Bridges

The tunneling magnetoresistance (TMR) angle sensors are employed in various applications as they offer noncontact measurement for full-circle range, consume low power, and have high sensitivity. These sensors provide sine- and cosine-natured nonlinear outputs with respect to the shaft angle. Therefore, a suitable electronic interface is required to estimate and obtain a linear indication of the shaft angle. In this article, one such interface, named, a faster digitizer for half-bridge-based TMR angle sensor (FDHTA), is discussed. The FDHTA utilizes a modified dual-slope-based technique which ensures a smaller conversion time while preserving measurement accuracy. This feature enables accurate measurement even for dynamic inputs. The FDHTA processes sine-cosine outputs from the sensor and renders a linear digital output, without using any explicit analog-to-digital converter (ADC). The measurement accuracy is least affected by a few sensor and circuit parameters. Apart from these features, a compensation technique is proposed to improve accuracy for one important sensor nonideality. The FDHTA is built on a PCB and tested extensively. The worst case nonlinearity, obtained for an ideal sensor, is 0.078%. Further, the FDHTA is found suitable for tracking dynamic inputs for shaft speeds up to 240 r/min with acceptable error. In experimentation, the output nonlinearity is observed to follow the inherent nonlinearity of the TMR angle sensing unit (SU). The FDHTA parameters such as standard deviation (SD), signal-to-noise ratio (SNR), etc., are observed to be at par or better when compared with the existing digitizers. The FDHTA can be employed for position estimation of the steering wheel, rotary valves, antenna, camera, surveillance equipment, etc.