Digital demodulator for continuously phase or frequency modulated signals

Abstract From the Canadian patent

A frequency and phase demodulating circuit provides direct frequency demodulation utilizing only addition subtraction and, multiplication steps. Division of signals is avoided as is the, need for a look-up table of trigonometric values corresponding to the results of such division. By maintaining a substantially constant input amplitude to a quadrature sampler a number of, approximations may be made without introduction of error. Compensation for actual signal variation as well as for first order, errors due to the approximation process of the invention results in, accurate frequency evaluation and avoids the necessity for differentiating an initial phase determination.