Patent ID: 7193205

Claim:
A processing apparatus for use with an optical encoder, the apparatus comprising: a. a digital estimator for generating samples of phase, φ i according to the equation Φ ⁢ ⁢ i = ATAN ⁡ [ Yi Xi ] , X i and Y i being samples of quadrature signals received from the encoder, i being an integer having values from one to an integer n; b. a fringe counter for generating a count, the count increasing by one every time the phase, when measured modulo two pi, crosses from a fourth quadrant of a unit circle to first quadrant of the unit circle, the count decreasing by one every time the phase, when measured modulo two pi, crosses from the first quadrant of the unit circle to the fourth quadrant of the unit circle, the fourth quadrant extending from angles 3/2 pi to 2 pi, the first quadrant extending from angles zero to pi/2; c. a state generator that receives the count and the samples of phase φ i and generates in response thereto two burst output signals in A quad B format, each of the burst output signals being characterized at any point in time by either high value state or low value state, comprising: an interpolator that generates an integer number representative of the count and the phase φ i ; an accumulator that generates a running sum by counting transitions in the A quad B burst output signals; a comparator for generating a signed difference value representative of a difference between the integer number and the running sum; a burst generator that generates transitions in the A quad B burst output signals until the signed difference value is zero.