Proportional-delayed zero-crossing frequency-drift estimator devices are
provided. Given N-number of time samples, the current zero-crossing time
estimation technique uses only two zero-crossing time samples for
repetition-rate estimation. The term "zero-crossing point" refers to the
point where a sinusoidal waveform varies from a positive to a negative
value and crosses the zero value in the process. The proportional-delayed
zero-crossing frequency-drift estimator devices employ four zero-crossing
time samples by utilizing both proportional zero-crossing points for
current information and delayed zero-crossing points for past information
so that the noises in the time samples will be smoothed out making a less
noisy estimation. The proportional-delayed zero-crossing frequency-drift
estimators are composed of a hysteretic nonlinear converter, a
zero-crossing time-difference counter, a group of shift registers and
adders, a repetition-rate algorithm, a reciprocal operator and a means
for differentiation operation. A number of different embodiments are
provided, but all embodiments include a hysteretic nonlinear converter
which enhances the zero-crossing features and blocks the signal random
noise so that the zero-crossing point is measured more accurately.