Phase locked loop with rapid phase pull in

摘要

A frequency tuning arrangement for tuning a source of variable frequency to a desired frequency, comprises a phase lock loop having a reference frequency source, an adjustable divider dividing the variable frequency to produce an adjustable control frequency, a phase comparator for comparing the phases of the control and reference frequencies to produce a control signal dependent on any phase error detected, and adjusting means responsive to the control signal for adjusting the variable frequency so as to equalize the phases of the control and reference frequencies. In accordance with the invention, means responsive to the phase error imposes on the leading one of the control and reference frequencies a phase delay which is substantially equal to the phase error. This enables the system to respond very rapidly to changes in desired frequency.