Slow acting phase-locked loop with external control signal

A slow acting phase-locked loop adapted to vary the frequency of an output signal in response to control signals having frequency components well above the cut-off frequency of said slow acting phase-locked loop, said slow acting phase-locked loop comprising:

• controllable oscillator means for producing a high frequency oscillator signal in response to an oscillation control signal, said controllable oscillator having a linear frequency control law over a very narrow frequency band lying about a nominal high frequency;
• divider means connected to said oscillator means for dividing down the frequency of said oscillator signal to produce a low frequency loop signal having a frequency several orders of magnitude lower than the frequency of said high frequency oscillator signal and an output signal having a frequency lying in the range between said high frequency oscillator signal and said low frequency loop signal;
• reference signal means for producing a highly accurate and stable low frequency control signal having a frequency the same as the frequency of said low frequency loop signal;
• phase comparator means connected to said divider means and to said reference signal means for:
• (i) receiving said low frequency loop signal produced by said divider means and said highly accurate and stable low frequency control signal produced by said reference signal means;
• (ii) comparing said low frequency loop signal produced by said divider means and said highly accurate and stable low frequency control signal produced by said reference signal means;
• and, (iii) producing, in accordance therewith, a loop control signal having a very low magnitude ripple at the frequency of said low frequency control and loop signals and an overall magnitude related to the phase difference between said low frequency loop signal produced by said divider means and said highly accurate and stable low frequency control signal produced by said reference signal means;
• loop filter means connected to said phase comparator means for receiving and low frequency filtering in a low phase shift manner said loop control signal;
• and,
• summing means having a first input connected to receive the output of said loop filter means and a second input adapted to receive an external control signal having a frequency component lying above the cutoff frequency of said slow acting phase-locked loop, said summing means summing its input signals and producing an oscillator control signal in accordance therewith, said oscillator control signal applied to said controllable oscillator means for controlling the frequency of the high frequency oscillator signal produced by said controllable oscillator means.