Frequency synthesizer apparatus having automatic fine tuning

Claim 2

Frequency synthesizer apparatus including in combination means for producing a reference frequency signal; means for producing a displaced reference frequency signal differing from the reference frequency signal by a predetermined differential frequency; means for producing a differential frequency signal equal to said predetermined differential frequency; first harmonic generating means coupled to the means for producing the reference frequency signal for producing a plurality of harmonics of the reference frequency signal; second harmonic generating means coupled to the means for producing the displaced reference frequency signal for producing a plurality of harmonics of the displaced reference frequency signal; a voltage controlled oscillator; phase detector means having a first input coupled to the first harmonic generating means, a second input coupled to the output of the voltage controlled oscillator, and an output coupled to the input of the voltage controlled oscillator to provide a phase-locked loop, whereby the frequency of the output signal of the voltage controlled oscillator is equal to a harmonic of the reference frequency signal; tuning means coupled to the input of the voltage controlled oscillator for selectively tuning the voltage controlled oscillator to produce an output signal of a particular harmonic of the reference frequency signal; frequency mixing means coupled to the second harmonic generating means and to the output of the voltage controlled oscillator for frequency mixing the plurality of harmonics of the displaced reference frequency signal with the particular harmonic of the reference frequency signal; filtering means coupled to the output of the frequency mixing means for removing the high frequency components of frequency mixing and passing the particular harmonic of the differential frequency; and adjustment means coupled to the filtering means, the means for producing the differential frequency signal, and the input of the voltage controlled oscillator, said adjuStment means being operable to change the tuning of the voltage controlled oscillator to produce an output signal of another harmonic of the reference frequency signal when the particular harmonic of the differential frequency from the filtering means differs from the differential frequency signal by a multiple of other than a predetermined harmonic value.

Claim 3

Frequency synthesizer apparatus in accordance with claim 1 including oscillator means for producing an oscillator frequency signal; and frequency reducing means coupled to the oscillator means and operable to produce said reference frequency signal, said displaced reference frequency signal, and said differential frequency signal.

Claim 4

Frequency synthesizer apparatus in accordance with claim 1 wherein said adjustment means includes means for selectively setting the predetermined harmonic value; divider means coupled to the filtering means for producing an output signal of frequency equal to the particular harmonic of the differential frequency divided by said predetermined harmonic value; comparison means coupled to the divider means, to the means for producing the differential frequency signal, and to the input of the voltage controlled oscillator; said comparison means being operable to change the value of the harmonic of the reference frequency produced by the voltage controlled oscillator toward the predetermined harmonic value when the output signal from the divider means differs from the differential frequency signal.

Claim 5

Frequency synthesizer apparatus in accordance with claim 1 wherein said adjustment means includes dividing means coupled to the filtering means and operable to be selectively set to divide by a predetermined harmonic value, said dividing means being operable to produce an output signal of frequency equal to the particular harmonic of the differential frequency divided by said predetermined harmonic value as set therein; and comparing means coupled to said dividing means, to the means for producing the differential frequency signal, and to the input of the voltage controlled oscillator; said comparing means being operable to compare the output signal of the dividing means with the differential frequency signal and to adjust the voltage level at the input of the voltage controlled oscillator to change the harmonic of the reference frequency signal produced by the voltage controlled oscillator toward the predetermined harmonic value.

Claim 6

Frequency synthesizer apparatus in accordance with claim 4 including a voltage summing network having a first input from the phase detector, a second input from the coarse tuner, a third input from the comparing means, and an output to the voltage controlled oscillator; said voltage summing network being operable to combine the voltages received at the inputs thereto and to produce an output voltage equal to the sum of the input voltages; and wherein said comparing means is operable to increase the voltage level at the third input to the voltage summing network when the frequency of the output signal from the dividing means is less than the differential frequency, and to decrease the voltage level at the third input to the voltage summing network when the frequency of the output signal from the dividing means is greater than the differential frequency.

Claim 7

Frequency synthesizer apparatus in accordance with claim 5 including oscillator means for producing an oscillator frequency signal; and frequency reducing means coupled to the oscillator means and operable to produce said reference frequency signal, said displaced reference frequency signal, and said differential frequency signal.

Claim 8

Frequency synthesizer apparatus in accordance with claim 1 wherein said adjustment means includes means for selectively setting a representation of the predetermined harmonic value; means coupled to the filtering means and to the means for producing a differential frequency signal aNd operable to count the number of cycles of the particular harmonic of the differential frequency occurring during a pre-established number of cycles of the differential frequency; and means coupled to the input of the voltage-controlled oscillator and operable to compare the representation of the predetermined harmonic value with the count of the number of cycles of the particular harmonic of the differential frequency occurring during the pre-established number of cycles of the differential frequency, and to change the value of the harmonic of the reference frequency produced by the voltage controlled oscillator toward the predetermined harmonic value when the count differs from the count for a particular harmonic having the same value as the predetermined harmonic value.

Claim 9

Frequency synthesizer apparatus in accordance with claim 1 wherein said adjustment means includes counting means operable to count the cycles of an input signal; means for selectively setting a count representative of the predetermined harmonic value in said counting means; input gating means coupled to the filtering means and to the counting means; control means coupled to said means for producing a differential frequency signal and to said input gating means and operable to enable cycles from the filtering means to be counted by the counting means for a pre-established number of cycles of the differential frequency; said counting means being operable to produce signals representative of the magnitude and direction of the difference between the value of the predetermined harmonic as represented by the count set in the counter and the value of the particular harmonic as represented by the number of cycles of the particular harmonic of the differential frequency counted during the pre-established number of cycles of the differential frequency; and means coupled to the counting means and to the input of the voltage controlled oscillator and operable to apply a voltage related to the magnitude and direction of the difference in harmonic values as represented by the signals from the counting means to the input of the voltage controlled oscillator to change the harmonic of the reference frequency signal produced by the voltage controlled oscillator to the predetermined value.

Claim 10

Frequency synthesizer apparatus in accordance with claim 8 including tuning detection means coupled to the voltage controlled oscillator and to the counting means and operable to cause the counting means to terminate said signals therefrom when the value of the harmonic of the reference frequency produced by the voltage controlled oscillator becomes equal to the predetermined harmonic value.

Claim 11

Frequency synthesizer apparatus in accordance with claim 1 wherein said adjustment means includes counting means operable to count the cycles of an input signal and operable to produce an output signal when the count in the counting means is at zero; means for selectively setting an initial count corresponding to the value of the predetermined harmonic in said counting means; input gating means coupled to the filtering means and to the counting means; control means coupled to said means for producing a differential frequency signal and to said input gating means and operable to enable the input gating means to permit cycles of the signal from the filtering means to be counted for the period of a cycle of the differential frequency, the number of cycles of the signal from the filtering means during a cycle of the differential frequency corresponding to the value of the particular harmonic of the reference frequency; direction control means coupled to the counting means and operable to produce a first control signal when in a first condition and to produce a second control signal when in a second condition, said direction control means being normally set in the first condition and being operable to be switched to the second condition in response to an output signAl from said counting means; means coupled to the control means, to the direction control means, and to the counting means, said means being operable to cause the counting means to count downward during the period the control means is enabling the input gating means, being operable to cause the counting means to count downward when the control means is not enabling the input gating means and the direction control means is in the first condition, and being operable to cause the counting means to count upward when the control means is not enabling the input gating means and the direction control means is in the second condition; voltage generating means coupled to the control means, to the counting means, to the direction control means, and to the input of the voltage controlled oscillator, said voltage generating means being operable when the control means is not enabling the gating means and the counting means is not producing an output signal to produce a ramp voltage in one direction in response to a first control signal applied thereto from the direction control means and to produce a ramp voltage in the opposite direction in response to a second control signal applied thereto from the direction control means; and tuning detector means coupled to the voltage controlled oscillator and to the input gating means and operable to produce a signal for each change in the harmonic of the reference frequency caused by a ramp voltage applied to the input of the voltage controlled oscillator; said input gating means being operable to apply a pulse to the counting means in response to each signal thereto from the tuning detector means when the control means is not enabling the input gating means; said counting means being operable to count said pulses until a count of zero is reached and the value of the harmonic of the reference frequency produced by the voltage controlled oscillator equals the predetermined harmonic value whereby an output signal is produced thereby terminating the ramp voltage from the voltage generating means and preventing further changes in the frequency of the output signal of the voltage controlled oscillator.

Claim 12

Frequency synthesizer apparatus in accordance with claim 10 wherein said control means includes a bistable means which is switched alternately between first and second conditions during each cycle of the differential frequency signal; said bistable means being operable when in the first condition to enable the input gating means to permit cycles of the signal from the filtering means to be counted, to prevent pulses from the tuning detector means from being counted, to cause the counting means to count downward, and to prevent operation of the voltage generating means; said bistable means being operable when in the second condition to prevent cycles of the signal from the filtering means from being counted, to permit pulses from the tuning detector means to be counted, to permit the direction of counting of the counting means to be controlled by the condition of the direction control means, and to permit the voltage generating means to produce a ramp voltage.

Claim 13

Frequency synthesizer apparatus in accordance with claim 11 wherein said direction control means includes a bistable means coupled to the counting means and to the bistable means of said control means and having a first condition corresponding to the first condition of the direction control means and a second condition corresponding to the second condition of the direction control means, said bistable means of said direction control means being switched from the first condition to the second condition in response to an output signal from the counting means while the bistable means of the control means is in the first condition.