Phase-locked loop stabilized by a crystal oscillator
First Claim
1. Apparatus for providing at least one output frequency signal phase-locked to the frequency of an input signal, comprising:
- a phase detector having first and second inputs and an output having a signal related to the difference in phase between the signals at the first and second inputs;
input signal conditioning means receiving said input signal for providing a reference frequency signal to said first phase detector input;
means connected to the phase detector output for filtering said phase detector output signal;
means receiving the filtered output signal from the filtering means for generating a periodic waveform having a first frequency controlled by the magnitude of the filtered phase detector output signal;
crystal controlled oscillator means for providing a signal at a second frequency;
frequency-subtractive means having a first input receiving a sum-frequency signal and a second input receiving the second frequency signal for providing an output signal having a third frequency equal to the difference between said sum-frequency and second signal frequency;
frequency-arithmetic means receiving the third frequency signal for synthesizing said at least one output signal and for providing a loop signal for coupling to the second input of said phase detector for causing said waveform generating means frequency to vary and lock the frequency of said at least one output frequency to said input signal frequency;
said frequency-arithmetic means also providing a signal at a fourth frequency; and
means receiving the waveform generating means output signal and said fourth frequency signal for adding the first and fourth frequency signals to provide the sum-frequency input signal to the first input of the frequency-subtractive means.
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Abstract
A phase-locked loop circuit, having an oscillator controlled by a voltage related to the phase difference between a reference signal and a loop signal, is stabilized by a crystal oscillator. The voltage controlled oscillator signal is frequency-subtracted from the crystal oscillator signal frequency to provide an input signal to a frequency-arithmetic synthesizer which provides a loop signal to the phase detector for comparison with the coming reference signal. Use of a frequency-adder circuit between the voltage controlled oscillator and the frequency-subtractor, and receiving an addition frequency derived from the frequency-arithmetic synthesizing circuit, is utilized to decrease the loop gain and provide enhanced characteristics.
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Citations
14 Claims
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1. Apparatus for providing at least one output frequency signal phase-locked to the frequency of an input signal, comprising:
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a phase detector having first and second inputs and an output having a signal related to the difference in phase between the signals at the first and second inputs; input signal conditioning means receiving said input signal for providing a reference frequency signal to said first phase detector input;
means connected to the phase detector output for filtering said phase detector output signal;means receiving the filtered output signal from the filtering means for generating a periodic waveform having a first frequency controlled by the magnitude of the filtered phase detector output signal; crystal controlled oscillator means for providing a signal at a second frequency; frequency-subtractive means having a first input receiving a sum-frequency signal and a second input receiving the second frequency signal for providing an output signal having a third frequency equal to the difference between said sum-frequency and second signal frequency; frequency-arithmetic means receiving the third frequency signal for synthesizing said at least one output signal and for providing a loop signal for coupling to the second input of said phase detector for causing said waveform generating means frequency to vary and lock the frequency of said at least one output frequency to said input signal frequency;
said frequency-arithmetic means also providing a signal at a fourth frequency; andmeans receiving the waveform generating means output signal and said fourth frequency signal for adding the first and fourth frequency signals to provide the sum-frequency input signal to the first input of the frequency-subtractive means. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. Apparatus for providing at least one output frequency signal phase-locked to the frequency of an input signal, comprising:
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a phase detector having first and second inputs and an output having a signal related to the difference in phase between the signals at the first and second inputs; input signal conditioning means receiving said input signal for providing a reference frequency signal to said first phase detector input;
means connected to the phase detector output for filtering said phase detector output signal;means receiving the filtered output signal from the filtering means for generating a periodic waveform having a first frequency controlled by the magnitude of the filtered phase detector output signal; crystal controlled oscillator means for providing a signal at a second frequency; means having a first input receiving the first frequency signal and a second input receiving the second frequency signal for providing an output signal having a third frequency equal to difference between said first and second signal frequencies and comprising;
a first flip-flop logic element having a count input receiving said first frequency signal, a clear input and an output settable to a first logic level by the appearance of a signal at said count input and to a remaining logic level by the appearance of a signal at said clear input;
a second flip-flop logic element having a count input receiving said second frequency signal, a data input connected to the output of said first flip-flop logic element, a first output settable to said first and second logic levels responsive to the appearance of said first and second logic levels at said data input, and a second output, coupled to the clear input of the first flip-flop logic element and having a signal thereat which is the inverse of the signal at the first output of said second flip-flop logic element; and
a NOR gate having a first input connected to the first output of said second flip-flop logic element and a second input receiving said second frequency signal, and an output at which said output signal having a frequency equal to the difference between said first and second signal frequencies appears; andfrequency-arithmetic means receiving the third frequency signal for synthesizing said at least one output signal and for providing a loop signal for coupling to the second input of said phase detector for causing said waveform generating means frequency to vary and lock the frequency of said at least one output frequency to said input signal frequency.
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14. Apparatus for providing at least one output frequency signal phase-locked to the frequency of an input signal, comprising:
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a phase detector having first and second inputs and an output having a signal related to the difference in phase between the signals at the first and second inputs; input signal conditioning means receiving said input signal for providing a reference frequency signal to said first phase detector input;
means connected to the phase detector output for filtering said phase detector output signal;means receiving the filtered output signal from the filtering means for generating a periodic waveform having a first frequency controlled by the magnitude of the filtered phase detector output signal; crystal controlled oscillator means for providing a signal at a second frequency; means having a first input receiving the first frequency signal and a second input receiving the second frequency signal for providing an output signal having a third frequency equal to one of the sum and difference between said first and second signal frequencies; frequency-arithmetic means receiving the third frequency signal for synthesizing said at least one output signal and for providing a loop signal for coupling to the second input of said phase detector for causing said waveform generating means frequency to vary and lock the frequency of said at least one output frequency to said input signal frequency; auxiliary frequency-arithmetic means receiving signal frequencies from said synthesizing frequency-arithmetic means for providing an additional signal at said first frequency; and switch means activated to connect the first frequency receiving input of said third frequency providing means to the output of said additional frequent-arithmetic means whenever said input signal is not present at said apparatus.
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Specification