Analog position encoder

A position-measuring circuit is described for use with an analog position encoder of the kind comprising a code member and at least two sensors for sensing successive marks on the code member during relative movement between the code member and sensors, the sensors providing two oscillating quadrature signals. The circuit comprising means for obtaining a relatively coarse measure of position by detecting successive instants t 0 -t 3 at which the amplitudes of the sensor signals are equal or at which the amplitude of one signal is equal to the inverse of the amplitude of the other signal. The amplitude of one of the signals or its inverse is stored at each detection instant to alternately establish relatively high and low threshold levels. A fine measure of position at an arbitrary instant T is obtained as a function of the instantaneous amplitude P of one of the signals and the difference between neighbouring high and low thresholds levels.