Novel linearizer for tangent/cotangent converter

Abstract

Resolvers and other types of sinusoidal encoders provide electrical signals whose amplitudes are related to the sine and cosine of the mechanical shaft angle θ over the full 360° range. The tangent/cotangent converter, used with these transducers to extract θ from these signals, is based on the determination of a ratio between the absolute values of the sine and cosine signals. This produces highly non-linear output. In conventional converters, θ is determined from the output using a look up table or a processor. In this work, an analog shaping network is described for the linearization of this output and hence for linear determination of θ. The optimal break points positions of the shaping network are determined experimentally and automatically using a LabVIEW-based setup that seeks minimization of the overall absolute error of the converter. The absolute error was 0.14° over the full 360° range of input angle. The principle of operation, full circuit details, computer simulation and practical results are given.