Analysis of a tunnelling magneto-resistance-based angle transducer

An angle transducer that utilises tunnelling magneto-resistance (TMR) type sensor elements is presented and its performance is analysed. The signal conditioning circuit of the proposed angle transducer translates the sine-cosine outputs of a TMR sensor integrated circuit into an output that varies linearly with the sensing angle. An added advantage of the proposed scheme is that the output of the angle sensor is dictated, apart from the angle being sensed, only by a dc reference voltage. Thus good performance characteristics can be obtained from the proposed transducer very easily by using a precision dc voltage as the reference. Possible sources of errors that may affect the performance of the transducer are identified and their effects are quantified. Simulation studies conducted using SPICE demonstrates the ability of the scheme in providing a linear output across the entire 360° range. Experimental results obtained from a prototype unit built and tested, portray a worst-case error of < ±1.05%.

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