A delay-lock period estimator

If the derivative of a periodic signal approximated by its first difference, and the difference between the signal and its estimated one period delayed version are correlated, it is possible to find the period using a simple algorithm similar to the quantized delay-lock discriminator. The estimator uses a fixed number of allocations to store samples of the input, taken at a variable rate by a sampler controlled by the output of the differences´ correlator.