Practical Considerations and Performance Evaluation of An Offset Elimination Scheme for Half-Bridge TMR Angle Sensor

The Tunneling Magneto-Resistance (TMR) angle sensors are being widely used in several industries for different applications that require shaft angle measurement. These sensors are commercially available in two configurations, namely, half-bridge and full-bridge. The half-bridge based TMR angle sensors have a constant offset voltage in their sine-cosine natured outputs. Conventionally, this offset is eliminated using a pair of costly instrumentation amplifiers. In this paper, a simple technique is discussed to obtain offset-free sine-cosine natured outputs from the half-bridge type TMR angle sensor. This technique does not require costly instrumentation amplifiers and is well suited for temperature fluctuating environment. The modification in the scheme, required to obtain offset-free sine cosine outputs from a practical TMR angle sensor, is also mathematically described in detail. It is because of the ratiometric principle, the modified scheme can also withstand temperature fluctuations and render offset free outputs. Error analysis is also presented in this paper to highlight few important practical aspects of TMR angle sensors. SPICE-based simulation studies are carried out first to verify the performance of the technique. Later, a prototype shaft angle sensing unit, employing half-bridge TMR IC AAT003-10E, was built and characterized. The modified offset-elimination technique is then tested with the unit. The output voltages of the sensing unit are found to follow desired sine-cosine relationship with the shaft angle with minimal offset.