Precise Phase Demodulation Algorithm for Sinusoidal Encoders and Resolvers

Sinusoidal encoders and resolvers encode position information by providing a pair of sine and the cosine signals. In order to determine the position information, suitable phase demodulation algorithms should be applied to the sinusoidal signals. In this article, a precise phase demodulation algorithm is presented based on the linearization technique. Inspired by the good linearity of the sinusoidal signals around the null point, the proposed algorithm makes use of the linear sections of the original sinusoidal signals and the generated phase-shift signals to obtain a preliminary linearized signal. A compensation strategy is then provided to achieve a nearly perfect linearized signal, from which position information can be linearly determined without utilizing a lookup table. The whole linearization process is only involved with simple mathematical and logic operations on the input sinusoidal signals. It is illustrated that the phase demodulation error is less than 0.00003194° over 360° signal period (corresponds to approx. 23-bit accuracy per period), which implies a small negligible error. Furthermore, the proposed algorithm is implemented utilizing a field-programmable gate array, and experiments are performed to demonstrate its effectiveness.