Frequency synthesizer using spectrum shift interpolation

Claim 2

A frequency synthesizer for generating an output signal having a frequency which is variable in discrete steps over a prescribed frequency range, each step having a predetermined maximum size and including intermediate interpolation steps, said frequency synthesizer comprising: i. means for generating a signal having a frequency equal to a primary reference frequency; ii. means for generating an interpolation signal frequency; iii. frequency dividing means having a variable dividing ratio n, including means for coupling saId frequency dividing means to said means (ii), said frequency dividing means being responsive to said interpolation signal for generating a first output signal having a frequency equal to said interpolation signal frequency divided by a said variable dividing ratio n; iv. frequency generating means coupled to said means (i) and said means (iii) for generating a secondary reference signal having a frequency equal to said primary reference signal frequency displaced by the frequency of said first output signal; v. a controllable oscillator for producing said output signal and including a frequency control means for tuning said controllable oscillator across a predetermined frequency range and for locking said output signal frequency to a predetermined frequency within said predetermined frequency range; vi. programmable signal generator means for generating a programming signal having a frequency equal to a unique value when said controllable oscillator output signal has a frequency equal to said predetermined frequency; vii. harmonic selection means for phase-locking said output signal frequency to a harmonic of said secondary reference signal frequency including means for coupling said harmonic selection means to said secondary reference signal and to said programming signal, said harmonic selection means being responsive to said programming signal for producing a control signal for operating said frequency control means so that said output signal is phase-locked on the selected harmonic of said secondary reference signal frequency; and viii. said frequency control means being connected to said harmonic selection means and responsive to said control signal for establishing the frequency of said output signal at said predetermined frequency when said programming signal frequency is equal to said unique value.

Claim 3

A frequency synthesizer as claimed in claim 1, in which said interpolation signal frequency is equal to a multiple of a subharmonic of said primary reference signal frequency.

Claim 4

A frequency synthesizer as claimed in claim 2, in which said subharmonic of said primary reference signal frequency has a value formed by raising the number 10 to an integral power thereby providing an interpolation signal frequency which is decimally related to said primary reference signal frequency.

Claim 5

A frequency synthesizer as claimed in claim 1, in which said output signal frequency is variable in discrete steps which have a maximum size equal to an integral multiple of said primary reference signal frequency.

Claim 6

A frequency synthesizer as claimed in claim 1, in which the frequency of said output signal is displaced in frequency by an amount equal to the frequency of said interpolation signal from a selected harmonic of said primary reference signal frequency, said selected harmonic having a harmonic number equal to said variable dividing ratio n.

Claim 7

A frequency synthesizer as claimed in claim 1, in which said secondary reference signal is generated by a mixing means coupled to said primary reference signal and to said first output signal, said mixing means being operable for comparing the frequency of said primary reference signal and the frequency of said first output signal to produce a second output signal, said second output signal containing a plurality of frequencies including said primary reference signal frequency said first output signal frequency, and the difference frequencies between said primary reference signal frequency and said first output signal frequency, and further including filter means coupled to said second output signal, said filter means being used for generating a signal having a frequency equal to said primary reference signal frequency displaced by the frequency of said first output signal.

Claim 8

A frequency synthesizer as claimed in claim 1, in which said frequency generating means for generating said secondary reference signal frequency includes: i. an auxiliary controllable oscillator for generatIng a second output signal including a second frequency control means for tuning said auxiliary controllable oscillator across a predetermined frequency range and for locking said second output signal to said secondary reference signal frequency; ii. first mixing means coupled to said auxiliary controllable oscillator and coupled to said primary reference signal for producing a third output signal having a frequency equal to the difference between the frequency of said primary reference signal frequency and said second output signal frequency; iii. second comparing means being coupled to said first output signal and to said third output signal for producing a second control signal; and iv. said second frequency controlling means being connected to said second comparing means and being responsive to said second control signal for establishing the frequency of said second output signal at a value so that the frequency of said third output signal equals the frequency of said first output signal.

Claim 9

A frequency synthesizer as claimed in claim 1, in which the interpolation signal frequency is equal to the sum of a subharmonic of said primary reference frequency plus a frequency equal to an integer multiple of the primary reference signal frequency.

Claim 10

A frequency synthesizer system as claimed in claim 1, comprising in combination a first frequency synthesizer system as claimed in claim 1 and a second similar frequency synthesizer system in which said means for generating said interpolation signal frequency for said first frequency synthesizer system includes: said second frequency synthesizer system, means for coupling the means for generating said primary reference frequency and said programmable signal generator means for said first frequency synthesizer system to said second frequency synthesizer system, means for coupling said output signal generated by said controllable oscillator in said second frequency synthesizer system to a second frequency dividing means having a predetermined dividing ratio, said second frequency dividing means being operable for generating a second output signal having a frequency equal to a submultiple of the frequency of said output signal generated by said controllable oscillator in said second frequency synthesizer system said second output signal being the interpolation signal for said first frequency synthesizer system, thereby establishing the frequency of said interpolation signal for said first frequency synthesizer system at a frequency which is harmonically related to said primary reference signal frequency.

Claim 11

A frequency synthesizer system as claimed in claim 9, in which said second predetermined dividing ratio is equal to an integer which is an integral multiple of the number 10, said integral multiple having a value equal to the number of complete frequency decades covered by said predetermined frequency range for said controllable oscillator in said second frequency synthesizer system, thereby providing an interpolation signal frequency which is a decimal harmonic of said primary reference signal frequency.

Claim 12

A frequency synthesizer system as claimed in claim 9, wherein said means for coupling the means for generating said primary reference frequency and said programmable signal generator means for said first frequency synthesizer system to said second frequency synthesizer system include third and fourth frequency divider means respectively, each having the same predetermined dividing ratio for generating output signals having a frequency equal to a submultiple of said primary reference frequency and of said programming signal frequency respectively for said first frequency synthesizer system, thereby establishing the primary reference signal frequency and the programming signal frequency for said second frequency synthesizer system at a subharmonic of the primary reference signal frequency and the programming signal frequency respectively for said first frequency synthesizer system.

Claim 13

A frequEncy synthesizer system as claimed in claim 11, in which said third and fourth predetermined dividing ratios are equal to an integer which is an integral multiple of the number 10, said integral multiple having a value equal to the number of complete frequency decades covered by said predetermined frequency range for said controllable oscillator in said second frequency synthesizer system thereby providing an interpolation signal frequency which is a desired harmonic of said primary reference signal frequency.

Claim 14

A frequency synthesizer as claimed in claim 1, in which said means for generating said interpolation signal includes: i. a controllable interpolation oscillator for producing a second output signal having a variable frequency, said interpolation oscillator including a second frequency control means for tuning said interpolation oscillator over a prescribed frequency range and locking the frequency of said second input signal to said interpolation signal frequency; ii. gated frequency divider means coupled to said interpolation oscillator and having a variable dividing ratio programmed to divide the frequency of said second output signal by a factor decimally related to said required interpolation frequency for producing a third output signal having a frequency equal to a selected sub-harmonic of said interpolation signal frequency; iii. fixed frequency dividing means coupled to said primary reference signal frequency for producing a fourth output signal having a frequency equal to a sub-harmonic of said primary reference signal frequency equal to said selected subharmonic; iv. comparing means coupled to said gated frequency divider means and said fixed frequency dividing means, said comparing means being responsive to said third and fourth output signals for generating a second control signal; and v. means coupling said second frequency control means to said comparing means, said second frequency controlling means being responsive to said second control signal for establishing the frequency of said second output signal at a frequency equal to said interpolation signal frequency.

Claim 15

A frequency synthesizer as claimed in claim 13, in which the smallest incremental decimal step in the interpolation signal frequency corresponds to said sub-harmonic of said primary reference frequency.

Claim 16

A frequency synthesizer system for generating a signal having a frequency which differs from a selected harmonic of a reference frequency by a fixed offset frequency which includes: i. means for producing a first harmonic spectrum containing harmonics of a primary reference frequency; ii. controllable signal generator means for producing a second harmonic spectrum containing harmonics of a auxiliary reference frequency; iii. a controllable oscillator for generating a first output signal of variable frequency f1 and including a first frequency control means for tuning said controllable oscillator over a predetermined frequency range and for locking said first output signal to a predetermined frequency, said frequency range including a selected portion of said second harmonic spectrum; iv. first circuit means coupled to said controllable oscillator and to said means (ii) for comparing the phase of said first output signal with the signal generated by said means (ii) and operable to produce a first control signal having an amplitude dependent on the relative phase difference between the first output signal and the signal generated by said means (ii), said amplitude having a unique value when the frequency difference between the first output signal and a selected harmonic in the second harmonic spectrum has a desired value; v. said first frequency control means being connected to said first circuit means and being responsive to said first control signal for establishing the frequency of said first output signal at said predetermined frequency when said first control signal has said unique value; vi. sweeping means Coupled to said first frequency control means and operable by said first control signal for sweeping the frequency of said first output signal across said second harmonic spectrum when said first output signal frequency is different from said predetermined frequency; vii. a second frequency control means having first and second signal inputs connected to said means (i) and to said means (ii) for comparing the frequency difference between the output signal frequency of said means (i) and (ii) with sub-harmonics of a programmed reference signal having a frequency equal to a first selected fixed frequency and for generating a second control signal; said second control signal being coupled to said means (ii) for controlling said second harmonic spectrum so that the harmonics in said second harmonic spectrum have a predetermined relationship with the harmonics in said first harmonic spectrum and one specific harmonic in said second harmonic spectrum differs in frequency from said selected harmonic in said first harmonic spectrum by said first selected fixed frequency; viii. second circuit means coupled to said controllable oscillator and to said means (i) for mixing said first output signal with frequencies in said first harmonic spectrum to produce a second output signal having a frequency equal to a second selected fixed frequency when said specific harmonic in said first harmonic spectrum differs in frequency from the frequency of said first output signal by an amount equal to said second selected fixed frequency; and ix. gate means coupled to said means (viii) and responsive to said second output signal and coupled to said means (iv) for producing a third control signal to enable said means (iv) when the frequency of said second output signal is within a predetermined frequency range centered about a frequency equal to said second selected frequency, wherein said means (iv) is enabled and generates said first control signal thereby establishing the frequency of said first output signal at said predetermined frequency which is equal to said selected harmonic in said first harmonic spectrum plus said first selected fixed frequency.

Claim 17

A frequency synthesizer system for generating a signal having a frequency which differs from a selected harmonic of a reference frequency by a fixed offset frequency which includes: i. means for producing a first harmonic spectrum containing harmonics of a primary reference frequency; ii. controllable signal generator means for producing a second harmonic spectrum containing harmonics of a auxiliary reference frequency; iii. a controllable oscillator for generating a first output signal of variable frequency f1 and including a first frequency control means for tuning said controllable oscillator over a predetermined frequency range and for locking said first output signal to a predetermined frequency, said frequency range including a selected portion of said second harmonic spectrum; iv. first circuit means coupled to said controllable oscillator and to said means (ii) for comparing the phase of said first output signal with the signal generated by said means (ii) and operable to produce a first control signal having an amplitude dependent on the relative phase difference between the first output signal and the signal generated by said means (ii), said amplitude having a unique value when the frequency difference between the first output signal and a selected harmonic in the second harmonic spectrum has a desired value; v. said first frequency control means being connected to said first circuit means and being responsive to said first control signal for establishing the frequency of said first output signal at said predetermined frequency when said first control signal has said unique value; vi. sweeping means Coupled to said first frequency control means and operable by said first control signal for sweeping the frequency of said first output signal across said second harmonic spectrum when said first output signal frequency is different from said predetermined frequency; vii. a second frequency control means having first and second signal inputs connected to said means (i) and to said means (ii) for comparing the frequency difference between the output signal frequency of said means (i) and (ii) with sub-harmonics of a programmed reference signal having a frequency equal to a first selected fixed frequency and for generating a second control signal; said second control signal being coupled to said means (ii) for controlling said second harmonic spectrum so that the harmonics in said second harmonic spectrum have a predetermined relationship with the harmonics in said first harmonic spectrum and one specific harmonic in said second harmonic spectrum differs in frequency from said selected harmonic in said first harmonic spectrum by said first selected fixed frequency; viii. second circuit means coupled to said controllable oscillator and to said means (i) for mixing said first output signal with frequencies in said first harmonic spectrum to produce a second output signal having a frequency equal to a second selected fixed frequency when said specific harmonic in said first harmonic spectrum differs in frequency from the frequency of said first output signal by an amount equal to said second selected fixed frequency; and ix. gate means coupled to said means (viii) and responsive to said second output signal and coupled to said means (iv) for producing a third control signal to enable said means (iv) when the frequency of said second output signal is within a predetermined frequency range centered about a frequency equal to said second selected frequency, wherein said means (iv) is enabled and generates said first control signal thereby establishing the frequency of said first output signal at said predetermined frequency which is equal to said selected harmonic in said first harmonic spectrum plus said first selected fixed frequency.