Phase lock loop having switchable filters and oscillators

DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawings, there is shown in FIG.
1 a conventional phase-lock circuit of the prior art consisting of a phase detector 10, a filter 12, and a voltage-controlled oscillator (VCO) 14.
Phase detector 10 compares the phase of the input signal with that of the output signal from VCO 14, and generates a pulse voltage, the width of which is directly proportional to the phase difference between the two signals.
Filter 12 converts the output pulse from phase detector 10 into a DC voltage to control the oscillation frequency of VCO 14.
Thus, an output signal F.
sub.
out is synchronized with an input signal F.
sub.
in such that the phase of the output signal is locked to the phase of the input signal.
One preferred embodiment of the present invention will be described hereinafter in detail.
FIG.
2 shows a block diagram of a phase-lock circuit in accordance with the present invention.
Phase/frequency detector 16 compares an input signal at terminal 18 with an output signal at terminal 20, and generates output pulses, the duty factor and frequency of which are determined by either a constant or a changing phase difference between the input and output signals.
Phase/frequency detector 16 (as opposed to purely a phase detector) has two modes of operation--that of phase detection and that of frequency detection.
The output thereof is proportional to phase difference for two close together frequencies and latched either high or low for frequency differences greater than 2:1.
The output pulses from phase/frequency detector 16 are applied to one of a plurality of loop filters 22 through 26 via switch 28.
The integrating constants of the filters are different from each other, and each filter has an own optimum pulse frequency range for converting the output pulses from phase/frequency detector 16 to a DC voltage for the best loop dynamics.
The control voltage outputs of filters 22 through 26 are connected to VCOs 30 through 34, over-range detector 36 and under-range detector 38