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Abstract

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.

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First Claim