US 4,568,888 A · PLL Fast frequency synthesizer with memories for coarse tuning and loop gain correction

Abstract

A phase-locked loop frequency synthesizer apparatus for providing an output signal whose frequency jumps from one value to another, at regular intervals of time. Coarse tuning circuitry couples a prescribed signal to the apparatus' voltage-controlled oscillator (VCO), to drive the VCO immediately to the correct frequency each time a new frequency is selected, thereby substantially reducing the apparatus' settling time. In addition, adaptive coarse tuning circuitry continuously updates the values of stored coarse tuning information for each possible frequency, to correct for any drifts in the VCO's voltage/frequency characteristic. A VCO gain normalizer circuit amplifies the error signal coupled to the VCO by an amount that varies with the selected frequency, so as to correct for any non-uniformities in the apparatus' various elements, particularly the VCO, and to thereby provide a uniform loop gain.

Claims41

Dependent claims

Phase-locked loop apparatus having a substantially uniform loop gain over its entire frequency range, comprising:

voltage-controlled oscillator means for producing an output signal having a selected frequency;
phase detector means for comparing the phases of the output signal and a reference signal, to produce an error signal representing any phase difference;
and
gain normalization means for amplifying the error signal by a selected gain factor that varies according to the frequency of the output signal and for coupling the amplified error signal to the voltage-controlled oscillator means, to controllably adjust the output signal frequency, wherein the gain factor is selected such that the phase-locked loop apparatus has a substantially uniform loop gain over its entire frequency range, the gain normalization means including
memory means for storing information indicating the desired gain factor for each of a plurality of possible output signal frequencies,
means for generating a frequency-select signal indicating the selected output signal frequency and for coupling the frequency-select signal to the memory means, and
amplifier means responsive to the gain factor information selected from the memory means by the frequency-select signal, for amplifying the error signal by the indicated gain factor.

4 more elements

Gain adjustment apparatus for use in a phase-locked loop of the kind that includes a voltage-controlled oscillator for producing an output signal having a selected frequency, a digital phase detector for producing a sequence of control pulses having durations proportional to any difference in phase between the output signal and a reference signal, and a loop filter for filtering an error signal in accordance with the sequence of control pulses to control the voltage-controlled oscillator, wherein the digital phase detector has a gain that varies in accordance with the frequency of the output signal, the gain adjustment apparatus comprising:

variable current source means for supplying a current whose magnitude is selected according to the frequency of the output signal produced by the voltage-controlled oscillator;
and
switch means actuated by the sequence of control pulses produced by the digital phase detector, for switching the current supplied by the variable current source means to produce a current pulse sequence for coupling to the loop filter;
wherein the loop filter filters the error signal for controlling the voltage-controlled oscillator in accordance with the current pulse sequence;
and wherein the magnitude of the current supplied by the variable current source means is selected to substantially compensate for the variability of the digital phase detector gain with frequency, whereby the phase-locked loop has a loop gain that is substantially uniform, regardless of the frequency of its output signal.

2 more elements

Phase-locked loop apparatus having a substantially uniform loop gain over its entire frequency range, comprising:

voltage-controlled oscillator means for producing an output signal having a selected frequency;
digital phase detector means for producing a sequence of control pulses having durations that vary both in accordance with any difference in phase between the output signal and a reference signal and in accordance with the selected frequency;
loop filter means for filtering an error signal in accordance with the sequence of control pulses, to control the voltage-controlled oscillator means;
variable current source means for supplying a current whose magnitude is selected according to the selected frequency of the voltage-controlled oscillator means;
and
switch means actuated by the sequence of control pulses produced by the digital phase detector means, for switching the current supplied by the variable current source means to produce a current pulse sequence for coupling to the loop filter means;
wherein the loop filter means filter the error signal for controlling the voltage-controlled oscillator means in accordance with the current pulse sequence;
and wherein the magnitude of the current supplied by the variable current source means is selected to substantially compensate for the variability of the digital phase detector means gain with frequency, whereby the phase-locked loop has a loop gain that is substantially uniform, regardless of the frequency of its output signal.

5 more elements

A gain adjustment method for use in a phase-locked loop apparatus of the kind that includes a voltage-controlled oscillator for producing an output signal having a selected frequency, a digital phase detector for producing a sequence of control pulses having durations proportional to any difference in phase between the output signal and a reference signal, and a loop filter for filtering an error signal in accordance with the sequence of control pulses to control the voltage-controlled oscillator, wherein the digital phase detector has a gain that varies in accordance with the frequency of the output signal, the gain adjustment method comprising steps of:

supplying a current whose magnitude is selected eaccording to the frequency of the output signal produced by the voltage-controlled oscillator;
and
switching the current supplied in the step of supplying, in accordance with the sequence of control pulses produced by the digital phase detector, to produce a current pulse sequence for coupling to the loop filter;
wherein the loop filter filters the error signal for controlling the voltage-controlled oscillator in accordance with the current pulse sequence;
and wherein the magnitude of the current supplied in the step of supplying is selected to substantially compensate for the variability of the digital phase detector gain with frequency, whereby the phase-locked loop has a loop gain that is substantially uniform, regardless of the frequency of its output signal.

2 more elements

A method for generating an output signal having a controllably-adjustable frequency, comprising steps of:

generating an output signal having a selected frequency;
comparing the phases of the output signal and a reference signal, to produce a sequence of control pulses having durations that vary both in accordance with any phase difference and in accordance with the selected frequency;
outputting an error signal in accordance with the sequence of control pulses, for use in the step of generating, to controllably adjust the output signal frequency;
supplying a current whose magnitude is selected according to the selected frequency;
and
switching the current supplied in the step of supplying, in accordance with the sequence of control pulses produced in the step of comparing, to produce a current pulse sequence for use in the step of outputting;
wherein the step of outputting outputs the error signal for use in the step of generating in accordance with the current pulse sequence;
and wherein the magnitude of the current supplied in the step of supplying is selected to substantially compensate for the variability of the control pulse duration with frequency.

5 more elements

Phase-locked loop frequency synthesizer apparatus adapted to generate an output signal having a controllably selectable frequency, comprising:

voltage-controlled oscillator means for generating an output signal having a frequency that is controllably variable over a predetermined frequency range;
phase detector means for comparing the phases of the output signal and a reference signal, and for producing an error signal representing any phase difference, the error signal being coupled to the voltage-controlled oscillator means to controllably vary the frequency and phase of the output signal so as to reduce the phase difference;
and
coarse tuning means for producing a dc coarse tuning signal for coupling to the voltage-controlled oscillator means, to effect a coarse selection of the output signal frequency, the coarse tuning means including
memory means for storing coarse tuning information indicating the nominal dc coarse tuning signal value required by the voltage-controlled oscillator means to provide each output signal frequency in the predetermined frequency range;
frequency selection means for generating a frequency-select signal indicating the selected output signal frequency and for coupling the frequency-select signal to the memory means;
signal generating means responsive to the coarse tuning information selected from the memory means by the frequency-select signal, for supplying the appropriate dc coarse tuning signal to the voltage-controlled oscillator means, to effect a coarse selection of the output signal frequency;
and
adaptive tuning means responsive to the error signal produced by the phase detector means, for adjusting the coarse tuning information stored in the memory means, the adaptive tuning means including
polarity detection means for detecting the polarity of the error signal immediately after the frequency selection means first selects a particular frequency and for producing a corresponding polarity signal;
and
adjustment means for adjusting the coarse tuning information stored in the memory means in accordance with the polarity signal, such that the error signal will be reduced whenever the frequency selection means again selects the particular frequency.

9 more elements

Phase-locked loop frequency synthesizer apparatus adapted to generate an output signal having a controllably selectable frequency, comprising:

voltage-controlled oscillator means for generating an output signal having a frequency that is controllably variable over a predetermined frequency range;
phase detector means for comparing the phases of the output signal and a reference signal, and for producing an error signal representing any phase difference, the error signal being coupled to the voltage-controlled oscillator means to controllably vary the frequency and phase of the output signal so as to reduce the phase difference;
and
coarse tuning means for producing a dc coarse tuning signal for coupling to the voltage-controlled oscillator means, to effect a coarse selection of the output signal frequency, the coarse tuning means including
memory means for storing coarse tuning information indicating the nominal dc coarse tuning signal value required by the voltage-controlled oscillator means to provide each output signal frequency in the predetermined frequency range;
frequency selection means for generating a frequency-select signal indicating the selected output signal frequency and for coupling the frequency-select signal to the memory means;
signal generating means responsive to the coarse tuning information selected from the memory means by the frequency-select signal, for supplying the appropriate dc coarse tuning signal to the voltage-controlled oscillator means, to effect a coarse selection of the output signal frequency;
and
adaptive tuning means responsive to the error signal produced by the phase detector means, for adjusting the coarse tuning information stored in the memory means;
wherein the memory means includes adjustable memory means and fixed memory means, both for storing coarse tuning information indicating the nominal signal value required by the voltage-controlled oscillator means to provide each output signal frequency in the predetermined range of frequencies, both memory means outputting selected coarse tuning information in accordance with the frequency-select signal, and the fixed memory means permanently storing its coarse tuning information;
the adaptive tuning means adjusts the coarse tuning information stored in the adjustable memory means;
the signal generating means is responsive to the coarse tuning information output by both the adjustable memory means and the fixed memory means, to generate the dc coarse tuning signal;
and
the voltage-controlled oscillator means includes means for summing together the error signal produced by the phase detector means and the dc coarse tuning signal produced by the signal generating means, to produce a sum signal for use in adjusting its output signal frequency.

11 more elements

A frequency synthesizing method comprising steps of:

generating an output signal having a selected frequency;
comparing the phases of the output signal and a reference signal, and producing an error signal representing any phase difference, the error signal being used in the step of generating, to controllably vary the frequency and phase of the output signal so as to reduce the phase difference;
producing a dc coarse tuning signal for use in the step of generating, to effect a coarse selection of the output signal frequency, the step of producing including steps of
storing coarse tuning information in a memory, the stored information indicating the nominal dc coarse tuning signal value required in the step of generating to provide each of a plurality of output signal frequencies;
selecting from the memory the stored information corresponding to a selected one of the plurality of output signal frequencies;
and
generating the dc coarse tuning signal in accordance with the coarse tuning information selected from the memory for use in the step of generating, to coarsely adjust the output signal frequency to the selected value;
and
adjusting the coarse tuning information stored in the memory, in accordance with the error signal produced in the step of comparing, the step of adjusting including steps of
detecting the polarity of the error signal immediately after the step of selecting first selects a particular frequency and producing a corresponding polarity signal;
and
adjusting the coarse tuning information stored in the memory in accordance with the polarity signal, such that the error signal will be reduced whenever the step of selecting again selects the particular frequency.

9 more elements

A frequency synthesizing method comprising steps of:

generating an output signal having a selected frequency;
comparing the phases of the output signal and a reference signal, and producing an error signal representing any phase difference, the error signal being used in the step of generating, to controllably vary the frequency and phase of the output signal so as to reduce the phase difference;
producing a dc coarse tuning signal for use in the step of generating, to effect a coarse selection of the output signal frequency, the step of producing including steps of
storing coarse tuning information in a memory, the stored information indicating the nominal dc coarse tuning signal value required in the step of generating to provide each of a plurality of output signal frequencies;
selecting from the memory the stored information corresponding to a selected one of the plurality of output signal frequencies;
and
generating the dc coarse tuning signal in accordance with the coarse tuning information selected from the memory for use in the step of generating, to coarsely adjust the output signal frequency to the selected value;
and
adjusting the coarse tuning information stored in the memory, in accordance with the error signal produced in the step of comparing;
wherein the memory used in the step of storing includes both an adjustable memory and a fixed memory, both for storing coarse tuning information indicating the nominal signal value required in the step of generating to provide each of the plurality of output signal frequencies, the fixed memory permanently storing its coarse tuning information;
the adaptive tuning means adjusts the coarse tuning information stored in the adjustable memory;
the step of selecting simultaneously selects stored information from both the adjustable memory and the fixed memory;
the step of generating the dc coarse tuning signal is performed in accordance with the coarse tuning information selected from both the adjustable memory and the fixed memory;
and
the step of generating an output signal includes a step of summing together the error signal produced in the step of comparing and the dc coarse tuning signal produced in the step of generating, to produce a sum signal for use in adjusting the output signal frequency.

12 more elements

Dependencies are inferred from the claim text.

PLL Fast frequency synthesizer with memories for coarse tuning and loop gain correction

Life of this patent

PLL Fast frequency synthesizer with memories for coarse tuning and loop gain correction

Life of this patent

Abstract

Claims41