Controlled frequency signal source apparatus including a feedback path for the reduction of phase noise
First Claim
1. A low phase noise signal source comprising:
- controlled oscillator means having an output terminal and a frequency control terminal, said controlled oscillator means for generating a periodic signal at a frequency determined by a frequency control signal supplied to said frequency control terminal;
a first feedback path including noise discriminator means connected for supplying a feedback signal from said output terminal of said controlled oscillator means to said frequency control terminal thereof, said noise discriminator means including phase detector means having first and second input ports and an output port, said first and second input ports of said phase detector means being connected for receiving at least a portion of the signal supplied at said output terminal of said voltage-controlled oscillator means, said phase detector means including means for supplying a signal at said output port thereof that is representative of the phase difference between signals supplied to said first and second input ports;
said noise discriminator means including time delay means for delaying an applied signal by a predetermined amount of time τ
, said time delay means connected to delay the signal coupled to one of said first and second input ports of said phase detector means from said output terminal of said controlled oscillator means;
said noise discriminator means including variable phase shift means having a phase shift control terminal and including means for shifting the phase of an applied signal by an amount determined by a phase shift control signal applied to said phase shift control terminal, said variable phase shift means being connected to shift the phase of the signal being coupled to one of said first and second input ports of said phase detector means from said output terminal of said controlled oscillator means;
said noise discriminator means further including phase shift control means for supplying said phase shift control signal to said variable phase shift means, said phase shift control means being responsive to the signal supplied at said output port of said phase detector means and supplying a signal representative thereof to cause said variable phase shift means to supply a phase shift that minimizes the signal at said output port of said phase detector means; and
signal coupling means for coupling said signal supplied at said output port of said phase detector means as said noise discriminator feedback signal that is coupled to said frequency control terminal of said controlled oscillator means, said signal coupling means including means for establishing said feedback signal as negative feedback.
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Abstract
A low phase noise signal source is disclosed which incorporates a voltage controlled oscillator (VCO) and a feedback network that, in effect, demodulates the VCO output signal and supplies negative feedback representative of the VCO signal noise to the VCO frequency control terminal. The feedback network includes a frequency discriminator of the type wherein a time delay network is connected to one input port of a phase detector, with the VCO output signal being supplied to the time delay network and the second input port of the phase detector. A variable phase shifter, responsive to the signal supplied by the phase detector, is included in one of the phase detector input paths to cause a zero crossover of the frequency discriminator transfer characteristic to occur at the frequency to which the VCO is tuned. By establishing predetermined relationships between the transmission poles and zeroes of the feedback network, normal VCO tuning characteristics are preserved while simultaneously decreasing VCO phase noise. Various arrangements for operating the signal source over a wide band of output frequencies are disclosed, including a low-noise phase-locked loop frequency synthesizer.
84 Citations
13 Claims
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1. A low phase noise signal source comprising:
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controlled oscillator means having an output terminal and a frequency control terminal, said controlled oscillator means for generating a periodic signal at a frequency determined by a frequency control signal supplied to said frequency control terminal; a first feedback path including noise discriminator means connected for supplying a feedback signal from said output terminal of said controlled oscillator means to said frequency control terminal thereof, said noise discriminator means including phase detector means having first and second input ports and an output port, said first and second input ports of said phase detector means being connected for receiving at least a portion of the signal supplied at said output terminal of said voltage-controlled oscillator means, said phase detector means including means for supplying a signal at said output port thereof that is representative of the phase difference between signals supplied to said first and second input ports;
said noise discriminator means including time delay means for delaying an applied signal by a predetermined amount of time τ
, said time delay means connected to delay the signal coupled to one of said first and second input ports of said phase detector means from said output terminal of said controlled oscillator means;
said noise discriminator means including variable phase shift means having a phase shift control terminal and including means for shifting the phase of an applied signal by an amount determined by a phase shift control signal applied to said phase shift control terminal, said variable phase shift means being connected to shift the phase of the signal being coupled to one of said first and second input ports of said phase detector means from said output terminal of said controlled oscillator means;
said noise discriminator means further including phase shift control means for supplying said phase shift control signal to said variable phase shift means, said phase shift control means being responsive to the signal supplied at said output port of said phase detector means and supplying a signal representative thereof to cause said variable phase shift means to supply a phase shift that minimizes the signal at said output port of said phase detector means; andsignal coupling means for coupling said signal supplied at said output port of said phase detector means as said noise discriminator feedback signal that is coupled to said frequency control terminal of said controlled oscillator means, said signal coupling means including means for establishing said feedback signal as negative feedback. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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Specification