Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural a.f.s. for a single oscillator
Patent
1990-02-12
1991-04-30
Grimm, Siegfried H.
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural a.f.s. for a single oscillator
331 14, 331 17, 331 25, 388911, H03L 7087, G11B 1928
Patent
active
050122045
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a phase-control circuit wherein the output terminal of a phase comparator that compares the actual frequency with the reference frequency is connected to the input terminal of a controlled oscillator.
U. Tietze and Ch. Schenk describe a phase-control circuit, called a phase-locked loop, on pages 683 to 684 of Halbleiter-Schaltungstechnik, 4th ed., Springer, 1978.
Phase-locked loops, often abbreviated PLL, are employed in compact-disk players for example to obtain a synchronizing signal for controlling the speed of a disk drive from the EFM signal, the data signal coded in accordance with an eight-to-fourteen code and optically read from the disk. The speed must be controlled in order to keep the data flowing at a constant bit rate.
One drawback is that the controlled oscillator in the loop must be adjusted to the reference frequency by compensating it manually when the player is manufactured, and manual adjustments are always complicated and expensive.
Another drawback becomes apparent only once the compact-disk player has been operating for a while, when the parameters for the individual components of the loop vary over time as the result of temperature drift or aging of the components and lead to a gradually and initially almost imperceptible deterioration in sound reproduction.
SUMMARY OF THE INVENTION
The object of the invention is accordingly to eliminate the disadvantageous manual adjustment of a phase-locked loop and to ensure smooth operation as independent as possible of component aging and temperature drift.
This object is attained in accordance with the invention in that the output terminal of another control stage is connected to the input terminal of the controlled oscillator, in that the output terminal from the controlled oscillator is connected to one input terminal of another phase comparator, the second input terminal of which is supplied with reference frequency and the output terminal of which is connected to the input terminal of the second control stage, in that the first control stage is separated from the controlled oscillator to compensate the loop automatically, in that the second control stage varies its output until the frequency at the output terminal from the controlled oscillator equals the reference frequency, and in that the second control stage retains this level subsequent to compensation independent of the output from the second phase comparator and the first control stage is reconnected to the input terminal of the controlled oscillator.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings,
FIG. 1 is a schematic block diagram showing the essential elements of one embodiment according to the present invention,
FIG. 2 is a schematic block diagram showing the essential elements of another embodiment of the present invention
FIG. 3 is a schematic block diagram showing the essential elements of a third embodiment, and
FIG. 4 is a schematic block diagram showing the essential elements of a fourth embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will now be described and its function explained with reference to the embodiment illustrated in FIG. 1.
The EFM signal in FIG. 1 is supplied to the input terminal of a phase comparator Pl, the output terminal of which is connected to the input terminal of a control stage R. The output terminal of a quartz oscillator OZ that generates a reference frequency BF is connected to the second input terminal of phase comparator P1 and to the second input terminal of another phase comparator P2, the first input terminal of which is connected to the output terminal of a controlled oscillator VCO, a voltage-controlled oscillator for example, which is connected to the output terminal of another control stage in the form of a microprocessor MP and by way of a controlled switch S to the output terminal of first control stage R. The input terminal E of microprocessor MP is connected to the output terminal of phase comparator P2. The control input terminal of
REFERENCES:
patent: 4388596 (1983-06-01), Yamashita
Baas Dieter
Storz Dieter
Deutsche Thomson-Brandt GmbH
Fogiel Max
Grimm Siegfried H.
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