Low-noise digitally tunable phase-locked loop frequency generator

Claim 1

A method of suppressing noises in the output of a digitally tunable high-frequency oscillator whose output frequency f A is controlled via a filter network by a phase discriminator receiving a relatively low comparison frequency from a reference source and a matching feedback frequency stepped down from said output frequency f A , at least one of the frequencies fed to said phase discriminator being adjustable for varying said output frequency f A in coarse and fine increments, comprising the steps of: generating an auxiliary frequency f H of the same order of magnitude as said output frequency f A ; modifying said auxiliary frequency f H by the same coarse increments as said frequency f A ; continuously producing a difference frequency f D =f A -f H ; and feeding a corrective voltage dependent on said difference frequency f D to a control input of said high-frequency oscillator over a path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond a limiting frequency of said filter network, said corrective voltage being fed to said control input through a blocking capacitor, comprising the further step of diminishing said corrective voltage ahead of said blocking capacitor by a compensating voltage proportional to a fine-increment adjustment of said output frequency f A .

Claim 2

A method of suppressing noises in the output of a digitally tunable high-frequency oscillator whose output frequency f A is controlled via a filter network by a phase discriminator receiving a relatively low comparison frequency from a reference source and a matching feedback frequency stepped down from said output frequency f A , at least one of the frequencies fed to said phase discriminator being adjustable for varying said output frequency f A in coarse and fine increments, comprising the steps of: generating an auxiliary frequency f H of the same order of magnitude as said output frequency f A ; modifying said auxiliary frequency f H by the same coarse increments as said frequency f A ; continuously producing a difference frequency f D =f A -f H ; and feeding a corrective voltage dependent on said difference frequency f D to a control input of said high-frequency oscillator over a path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond a limiting frequency of said filter network, said corrective voltage being fed to said control input through a blocking capacitor, comprising the further step of diminishing said corrective voltage ahead of said blocking capacitor by a compensating voltage proportional to a fine-increment adjustment of said output frequency f A .

Claim 3

A method of suppressing noises in the output of a digitally tunable high-frequency oscillator whose output frequency f A is controlled via a filter network by a phase discriminator receiving a relatively low comparison frequency from a reference source and a matching feedback frequency stepped down from said output frequency f A , at least one of the frequencies fed to said phase discriminator being adjustable for varying said output frequency f A in coarse and fine increments, comprising the steps of: generating an auxiliary frequency f H of the same order of magnitude as said output frequency f A ; modifying said auxiliary frequency f H by the same coarse increments as said frequency f A ; continuously producing a difference frequency f D =f A -f H ; and feeding a corrective voltage dependent on said difference frequency f D to a control input of said high-frequency oscillator over a path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond a limiting frequency of said filter network, said difference frequency f D being used as said feedback frequency.

Claim 4

A method of suppressing noises in the output of a digitally tunable high-frequency oscillator whose output frequency f A is controlled via a filter network by a phase discriminator receiving a relatively low comparison frequency from a reference source and a matching feedback frequency stepped down from said output frequency f A , at least one of the frequencies fed to said phase discriminator being adjustable for varying said output frequency f A in coarse and fine increments, comprising the steps of: generating an auxiliary frequency f H of the same order of magnitude as said output frequency f A ; modifying said auxiliary frequency f H by the same coarse increments as said frequency f A ; continuously producing a difference frequency f D =f A -f H ; and feeding a corrective voltage dependent on said difference frequency f D to a control input of said high-frequency oscillator over a path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond a limiting frequency of said filter network, said difference frequency f D being used as said feedback frequency.

Claim 5

A system for generating a digitally tunable high-frequency oscillation, comprising: a main oscillator having a control input and an output terminal for producing a high output frequency f A ; a first phase-locking loop connected between said output terminal and said control input; a phase discriminator in said phase-locking loop with a first input connected to a source of a relatively low comparison frequency, a second input connected to said output terminal via a step-down circuit converting said output frequency f A into a feedback frequency matching said comparison frequency, and a voltage output connected to said control input via a filter network whose limiting frequency varies monotonically with the output voltage of said phase discriminator; first selection means coupled to one of the inputs of said phase discriminator through a frequency divider for modifying the frequency applied thereto in coarse-tuning steps corresponding to relatively large increments of said output frequency f A ; second selection means coupled through a switching network and said frequency divider to one of the inputs of said phase discriminator for modifying the frequency applied thereto in fine-tuning steps corresponding to relatively small increments of said output frequency f A ; an ancillary oscillator emitting an auxiliary frequency f H of the same order of magnitude as said output frequency f A , said ancillary oscillator being provided with a second phase-locking loop including control means coupled with said first selection means for varying said auxiliary frequency f H in the same relatively large increments as said output frequency f A ; mixer means connected to the output terminal of said main oscillator and to a corresponding terminal of said ancillary oscillator for generating a difference frequency f D =f A -f H ; a frequency discriminator connected to said mixer means for converting said difference frequency f D into a corrective voltage; and circuit means feeding said corrective voltage to said control input over an impedance path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond the limiting frequency of said filter network.

Claim 6

A system for generating a digitally tunable high-frequency oscillation, comprising: a main oscillator having a control input and an output terminal for producing a high output frequency f A ; a first phase-locking loop connected between said output terminal and said control input; a phase discriminator in said phase-locking loop with a first input connected to a source of a relatively low comparison frequency, a second input connected to said output terminal via a step-down circuit converting said output frequency f A into a feedback frequency matching said comparison frequency, and a voltage output connected to said control input via a filter network whose limiting frequency varies monotonically with the output voltage of said phase discriminator; first selection means coupled to one of the inputs of said phase discriminator through a frequency divider for modifying the frequency applied thereto in coarse-tuning steps corresponding to relatively large increments of said output frequency f A ; second selection means coupled through a switching network and said frequency divider to one of the inputs of said phase discriminator for modifying the frequency applied thereto in fine-tuning steps corresponding to relatively small increments of said output frequency f A ; an ancillary oscillator emitting an auxiliary frequency f H of the same order of magnitude as said output frequency f A , said ancillary oscillator being provided with a second phase-locking loop including control means coupled with said first selection means for varying said auxiliary frequency f H in the same relatively large increments as said output frequency f A ; mixer means connected to the output terminal of said main oscillator and to a corresponding terminal of said ancillary oscillator for generating a difference frequency f D =f A -f H ; a frequency discriminator connected to said mixer means for converting said difference frequency f D into a corrective voltage; and circuit means feeding said corrective voltage to said control input over an impedance path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond the limiting frequency of said filter network.

Claim 7

A system for generating a digitally tunable high-frequency oscillation, comprising: a main oscillator having a control input and an output terminal for producing a high output frequency f A ; a first phase-locking loop connected between said output terminal and said control input; a phase discriminator in said phase-locking loop with a first input connected to a source of a relatively low comparison frequency, a second input connected to said output terminal via a step-down circuit converting said output frequency f A into a feedback frequency matching said comparison frequency, and a voltage output connected to said control input via a filter network whose limiting frequency varies monotonically with the output voltage of said phase discriminator; first selection means coupled to one of the inputs of said phase discriminator through a frequency divider for modifying the frequency applied thereto in coarse-tuning steps corresponding to relatively large increments of said output frequency f A ; second selection means coupled through a switching network and said frequency divider to one of the inputs of said phase discriminator for modifying the frequency applied thereto in fine-tuning steps corresponding to relatively small increments of said output frequency f A ; an ancillary oscillator emitting an auxiliary frequency f H of the same order of magnitude as said output frequency f A , said ancillary oscillator being provided with a second phase-locking loop including control means coupled with said first selection means for varying said auxiliary frequency f H in the same relatively large increments as said output frequency f A ; mixer means connected to the output terminal of said main oscillator and to a corresponding terminal of said ancillary oscillator for generating a difference frequency f D =f A -f H ; a frequency discriminator connected to said mixer means for converting said difference frequency f D into a corrective voltage; and circuit means feeding said corrective voltage to said control input over an impedance path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond the limiting frequency of said filter network, said impedance path including a blocking capacitor in series with a resistor.

Claim 8

A system for generating a digitally tunable high-frequency oscillation, comprising: a main oscillator having a control input and an output terminal for producing a high output frequency f A ; a first phase-locking loop connected between said output terminal and said control input; a phase discriminator in said phase-locking loop with a first input connected to a source of a relatively low comparison frequency, a second input connected to said output terminal via a step-down circuit converting said output frequency f A into a feedback frequency matching said comparison frequency, and a voltage output connected to said control input via a filter network whose limiting frequency varies monotonically with the output voltage of said phase discriminator; first selection means coupled to one of the inputs of said phase discriminator through a frequency divider for modifying the frequency applied thereto in coarse-tuning steps corresponding to relatively large increments of said output frequency f A ; second selection means coupled through a switching network and said frequency divider to one of the inputs of said phase discriminator for modifying the frequency applied thereto in fine-tuning steps corresponding to relatively small increments of said output frequency f A ; an ancillary oscillator emitting an auxiliary frequency f H of the same order of magnitude as said output frequency f A , said ancillary oscillator being provided with a second phase-locking loop including control means coupled with said first selection means for varying said auxiliary frequency f H in the same relatively large increments as said output frequency f A ; mixer means connected to the output terminal of said main oscillator and to a corresponding terminal of said ancillary oscillator for generating a difference frequency f D =f A -f H ; a frequency discriminator connected to said mixer means for converting said difference frequency f D into a corrective voltage; and circuit means feeding said corrective voltage to said control input over an impedance path bypassing said filter network for suppressing noises due to phase differences occurring at said filter network and varying at frequencies beyond the limiting frequency of said filter network, said impedance path including a blocking capacitor in series with a resistor.