Abstract: Separate phase (or frequency/phase) detectors are used in separate feedback loops of a phase-locked loop, one of the detectors having a dead zone and the other detector having no dead zone. The dead zone of the one detector, rather than being regarded as undesirable as in the prior art, is used to gradually shift the effective loop bandwidth of the phase-locked loop from a wide bandwidth to a narrow bandwidth without requiring any deliberate control action or switching circuitry.

Abstract: In a frequency synthesizer of the type having a phase locked loop, a variable frequency divider is coupled to the output of the phase locked loop and a variable divider for dividing a reference signal is coupled to a frequency source for the frequency synthesizer. The phase lock loop also includes a variable divider for dividing the signal fed back from a voltage controlled oscillator to a phase detector. The division numbers or divisors of the variable frequency dividers are controlled such that a predetermined relationship exists among the frequency dividers. The frequency synthesizer is capable of switching reference frequencies without causing phase jumps. The reference frequency is selected depending upon the choice of a division number for the frequency divider coupled to the output of the frequency synthesizer.

Abstract: A frequency synthesizing apparatus comprising a reference generator (1) and a phase locked loop containing a phase detector (3) of the sample-hold type, a loop filter (4) a VCO (5) and a frequency divider (6) in the loop. The frequency divider (6) can be set at different numbers (N) so that the VCO sends different frequencies. In accordance with the invention a synchronizing unit (2) is connected between the reference generator (1) and the phase detector (3). The synchronizing unit switches reference generator (1) and the frequency divider means simultaneously to the phase locked loop during the locking phase and switches these out during a working phase, when the VCO (5) sends an output signal of the desired frequency (f). The loop filter can then be dimensioned with a wide bandwidth for rapid locking.