Rose Communications, Inc.

Roger J Eline

Bradley C Stribling

A phase locked loop is augmented by an additional mechanism which permits the closed loop cancellation of the frequency perturbing effects on the oscillator by repetitive signals well beyond the bandwidth of the phase locked loop. Successful implementation requires that the perturbations be repetitive and that the perturbing signal be available as a reference, conditions which are commonly the case. This compound loop can effectively cancel perturbations whose dynamics change only slowly compared to the speed of the added synchronous loop. The Anti-Pulling Loop mechanism consists of an amplifier to increase the level of the evidence of the perturbations present at the phase detector's output, a synchronous amplitude detector to correlate the perturbations with a reference signal, a circuit for the generation of a suitable quadrature reference signal, a loop integrator for the control of a signal injection mechanism, and a signal injection circuit to supply an appropriate signal to oppose and cancel the effects of the perturbing signal.

Method and apparatus for perturbation cancellation of a phase locked

A comparator-based digital data separator is modified to operate in noisy signal environments, with signals characterized by extreme duty cycle. A demodulated binary signal is passed through a pair of diodes which produce a slack voltage. The signal is then passed through an RC low-pass filter, and is finally connected to an input of the comparator as the reference voltage. The low-pass filter, which provides the D.C. averaged voltage to the threshold comparator, receives current into its own input only when the demodulated signal excursions exceed the existing threshold voltage by more than the slack voltage. Consequently, assuming there exists a sufficiently large recovered signal, the voltage being used as the decision threshold will remain separated from the recovered signal excursion peaks by at least the amount of slack voltage. In so doing, the binary data separation is given improved noise immunity and reduced sensitivity to duty cycle variations.

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Los Gatos, CA, United States of America

Roger J Eline