Phase locked loop with D.C. modulation

Details Phase locked loop with D.C. modulation Phase locked loop with D.C. modulation

1992-08-31

1994-05-10

Grimm, Siegfried H.

Modulators

Frequency modulator

Including stabilization or alternatively distortion, noise...

331 23, 331 25, 332128, 455113, H03C 309, H03L 7197

Patent

active

053111524

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates generally to phase locked oscillators and voltage controlled crystal oscillators. More particularly, the present invention relates to a phase locked loop with D.C. modulation, and uses of the D.C. modulated phase locked loop in such electrical devices as single frequency transmitters and channelized transmitters.


BACKGROUND ART

The frequency of radio frequency voltage controlled oscillators (RF VCO) has been closely controlled by phase locking a feedback signal from the RF VCO to a crystal controlled reference oscillator (XO). A phase detector has been used to determine the phase difference between the feedback signal and a crystal controlled reference frequency; and an integrator has been used to summate the phase difference and to control the frequency of the RF VCO oscillator in accordance with the summated phase difference.
Improvements taught by the prior art over the basic phase locked oscillator include the use of prescalers to provide a feedback signal having a lower frequency than the RF VCO, thereby lowering the required frequency of the controlling circuitry. Prior art improvements over the basic circuitry also include the use of a dual modulus divider to channelize the output frequency by dividing the feedback by higher and lower dividing ratios in a technique known as pulse swallowing. That is, a pulsed signal, having a frequency proportional to the output frequency, is provided in the feedback path, and channelizing is accomplished by swallowing, or removing, pulses in the feedback path.
While phase locked oscillators have provided a frequency output that drifts very little, a significant problem has been in trying to frequency modulate the output on a D.C. basis.
One attempt at D.C. modulating the frequency output of a phase locked oscillator has been to use a voltage controlled crystal oscillator (VCXO) in place of a crystal controlled reference oscillator (XO), and to simultaneously modulate the RF VCO as well as the VCXO. The problems with this approach have been non-linearities in the VCXO, limited frequency deviation, limited frequency response of modulation, and significantly increased frequency drift as a function of both time and temperature.
In stark contrast to the limitations of the prior art, the present invention provides highly linear D.C. modulation of a RF VCO together with very little frequency drift as well as almost unlimited deviation and frequency response.
More particularly, the present invention provides both single frequency and channelized phase locked loops that are capable of D.C. modulation.


DISCLOSURE OF INVENTION

In the present invention, a D.C. modulated phase locked RF VCO includes a phase locked loop with a forward path, an RF VCO in the forward path that produces an output, a feedback path that is connected to the output, a crystal controlled reference oscillator, a phase detector that is connected to the crystal controlled reference oscillator and that is connected to both the feedback path and the forward path, and an integrator in the forward path that controls the frequency of the voltage controlled oscillator in response to integrated differences in the phase between said reference oscillator and the frequency in the feedback path.
The means for D.C. modulating the RF VCO includes a dual modulus divider that is interposed into the feedback path, and a modulation oscillator that is connected to the dual modulus divider and that causes the dual modulus divider to divide by a higher dividing ratio for each cycle of the audio oscillator. Preferably, the modulation oscillator is a voltage controlled audio oscillator (AF VCO).
Therefore, the dual modulus divider cooperates with the voltage controlled audio oscillator to remove one pulse from the feedback path for each cycle of the audio oscillator. That is, the output frequency is used to provide a pulsed signal in the feedback path that is proportional to the output frequency, and one of these pulses is removed for each cycle, or pulse, of the modulation o

REFERENCES:
patent: 3622913 (1969-10-01), Shipley
patent: 3805192 (1974-04-01), Ocnaschek et al.
patent: 4068198 (1978-01-01), Otto
patent: 4068199 (1978-01-01), Madoff
patent: 4543542 (1985-09-01), Owen
patent: 4546331 (1985-10-01), DaSilva et al.
patent: 4581749 (1986-04-01), Carney et al.
patent: 4870384 (1989-09-01), Thomas

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