Fractional and rapid response frequency synthesizer, and corresponding frequency synthesizing method

A method of synthesizing frequencies by means of a frequency synthesizer, comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12),
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator and the phase-frequency comparator, in which the voltage controlled oscillator comprises a plurality of oscillator stages having different center frequencies,
• means for selecting (13, 50) an oscillator stage,
• characterized in that said method comprising a calibration step of the selection during which the phase-locked loop is open, and a frequency synthesizing step during which the phase-locked loop is closed.

A frequency synthesizer comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12) and
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator (12) and the phase-frequency comparator (16),
• characterized in that the voltage-controlled oscillator comprises a plurality of oscillator stages which have different center frequencies, in that the synthesizer further includes means for selecting (13, 50) an oscillator stage as a function of the integral component of the mean dividing ratio, in that the selection means comprise a logic table (50) connecting, respectively, the integral parts of the dividing ratio of the frequency divider to selections of stages of the voltage-controlled oscillator, and in that the selection means comprise a logic pointer (51) controlled by a data corresponding to the integral part of the dividing ratio, and associated to the logic table for selecting a stage of the voltage-controlled oscillator.

A frequency synthesizer comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12) and
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator (12) and the phase-frequency comparator (16),
• characterized in that the voltage-controlled oscillator comprises a plurality of oscillator stages which have different center frequencies, in that the synthesizer further includes means for selecting (13, 50) an oscillator stage as a function of the integral component of the mean dividing ratio, and in that the center frequencies of the voltage-controlled oscillator stages conform to an arithmetical progression and in which a calibration means comprise a first and a second counter (64a, 64b), clocked by the voltage-controlled oscillator (12) associated to the frequency divider (14) and by the reference frequency source (20), respectively, a subtracter (68) connected to the counters for establishing a counting difference, and means (70, 72) for correcting a selection as a function of the counting difference.

A method of synthesizing frequencies by means of a frequency synthesizer, comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12),
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator and the phase-frequency comparator,
• in which the voltage controlled oscillator comprises a plurality of oscillator stages having different center frequencies, and in which one of the stages of the voltage-controlled oscillator is selected as a function of the integral value of the mean dividing ratio of the frequency divider, wherein said method comprises a calibration step of the selection during which the phase-locked loop is open, and a frequency synthesizing step during which the phase-locked loop is closed.

A frequency converter comprising a mixer (200) which has a first input connected to a first signal source (202, 204) delivering a signal that has a frequency to be converted, and comprising a second signal source (1) which has a reference frequency, the second source being connected to a second mixer input, wherein the second signal source (1) having a reference comprises a frequency synthesizer (12) comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12) and
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator (12) and the phase-frequency comparator (16),
• characterized in that the voltage-controlled oscillator comprises a plurality of oscillator stages which have different center frequencies, in that the synthesizer further includes means for selecting (13, 50) an oscillator stage as a function of the integral component of the mean dividing ratio, in that the selection means comprise a logic table (50) connecting, respectively, the integral parts of the dividing ratio of the frequency divider to selections of stages of the voltage-controlled oscillator, and in that the selection means comprise a logic pointer (51) controlled by a data corresponding to the integral part of the dividing ratio, and associated to the logic table for selecting a stage of the voltage-controlled oscillator.

A portable telephone comprising a frequency converter having a mixer (200) which has a first input connected to a first signal source (202, 204) delivering a signal that has a frequency to be converted, and a second signal source (1) which has a reference frequency, the second source being connected to a second mixer input, wherein the second signal source (1) having a reference comprises a frequency synthesizer (12) comprising in a phase-locked loop:

• a phase-frequency comparator (16) connected to a reference frequency source (20),
• at least a voltage-controlled oscillator (12) and
• a fractional frequency divider (14) suitable for producing a mean dividing ratio having an integral component and a fractional component, the frequency divider being connected between the voltage-controlled oscillator (12) and the phase-frequency comparator (16),
• characterized in that the voltage-controlled oscillator comprises a plurality of oscillator stages which have different center frequencies, in that the synthesizer further includes means for selecting (13, 50) an oscillator stage as a function of the integral component of the mean dividing ratio, in that the selection means comprise a logic table (50) connecting, respectively, the integral parts of the dividing ratio of the frequency divider to selections of stages of the voltage-controlled oscillator, and in that the selection means comprise a logic pointer (51) controlled by a data corresponding to the integral part of the dividing ratio, and associated to the logic table for selecting a stage of the voltage-controlled oscillator.