A Linearizing Analog Front-End for Sine-Cosine Shaft Encoder

Encoders, possessing sine-cosine relationship with the shaft angle, are used in numerous applications. Such encoders, being non-linear, are often equipped with a front-end circuit to obtain a linear output. In this paper, an analog front-end, with full-circle range, is proposed for encoders with sine-cosine characteristic. The front-end performs a simple transformation on the high sensitivity regions of the encoder outputs and renders a linearly varying analog output. The worst-case non-linearity in the output, obtained using the linear transformation, is 0.605%. This linearity error is acceptable for several applications and therefore, proposed front-end can be employed in such cases. The working methodology of the front-end is discussed in detail. Extensive simulation and emulation based studies are conducted to verify working of the front-end for static as well as step input. Tunneling Magneto-Resistance (TMR) angle sensors possess sine-cosine dependency on the shaft angle. Therefore, a shaft angle sensing unit, using TMR angle sensor IC, is fabricated and tests are conducted. In experimentation also, the output of proposed front-end is shown to vary linearly for full-circle range.