Oscillators – Automatic frequency stabilization using a phase or frequency... – Plural a.f.s. for a single oscillator
Reexamination Certificate
2000-05-11
2002-12-24
Mis, David C. (Department: 2817)
Oscillators
Automatic frequency stabilization using a phase or frequency...
Plural a.f.s. for a single oscillator
C331S00100A, C331S014000, C331S025000, C331SDIG002, C327S156000, C327S159000
Reexamination Certificate
active
06498536
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an oscillator and, more particularly, to an oscillator for an oscillating signal synchronous with an input signal.
DESCRIPTION OF THE RELATED ART
A monitor display is usually connected to a personal computer. A video signal is supplied to the monitor display, and carries pictures at synchronizing frequencies depending upon the number of pixels defined in a VGA (Variable Graphic Array) or an SVGA (Super Variable Graphic Array), by way of example. Even though the video signal is supplied to the monitor display at different synchronizing frequencies, it is necessary that the picture size and the location of the picture are stable on the screen of the monitor display. For this reason, a multi-sink monitor display is widely used for the video signal supplied at different frequencies.
A synchronous signal processing circuit is integrated on a semiconductor chip, and the semiconductor integrated circuit device is incorporated in the multi-sink monitor display. The synchronous signal processing circuit achieves an automatic regulation for the horizontal output frequency, and the automatic horizontal frequency regulation circuitry is responsive to variation of the horizontal input frequency so as to make the free running oscillating frequency follow the horizontal input frequency. The phase and the frequency of the free running oscillating signal are coincident with those of the horizontal input signal.
FIG. 1
illustrates the prior art automatic horizontal frequency regulation circuitry. The prior art automatic horizontal frequency regulation circuitry comprises a counter
51
, a digital-to-analog converter
52
, a voltage-controlled oscillator
53
and a phase comparator
54
. The counter
51
is connected to the digital-to-analog converter
52
, which in turn is connected to the voltage-controlled oscillator
53
. The voltage-controlled oscillator
53
and a signal input node are connected to the phase comparator, and the phase comparator
54
regulates the oscillation frequency through the comparison between the input signal at the input node
101
and the free-running oscillation signal
503
.
The prior art automatic horizontal frequency regulation circuitry behaves as follows.
FIG. 2
shows the relation between the input frequency and a control voltage signal
502
. The digital-to-analog converter
52
linearly increases the magnitude of the control voltage signal
502
together with the input frequency, and the counter
51
and the digital-to-analog converter
52
uniquely determines the magnitude of the control voltage signal
502
on the basis of the input frequency. On the other hand, the relation between the control voltage signal
502
and the free-running oscillation signal
503
is shown in FIG.
3
. The frequency f
0
is linearly increased together with the magnitude of the control voltage signal
502
. Thus, the voltage-controlled oscillator
52
uniquely determines the free-running oscillation frequency on the basis of the magnitude of the control voltage signal. When the gradient of the plots is appropriately regulated, the voltage-controlled oscillator
53
varies the frequency of the free-running oscillation signal
503
in such a manner as to become coincident with the input frequency.
A problem is encountered in the prior art automatic horizontal frequency regulation circuitry in that a post regulation is required after the completion of the fabrication process. In detail, the voltage-controlled oscillator
53
repeats the charge into capacitors and the discharge therefrom for oscillating the free-running signal. The circuit components of the prior art automatic horizontal frequency regulation circuitry are integrated on a semiconductor chip through the fabrication process, and the capacitors are also formed on the semiconductor chip. However, the capacitance is liable to be dispersed, and the relation between the magnitude of the control voltage signal and the free-running frequency is not constant among the products. For example, if the voltage-controlled oscillator
53
is designed as indicated by real line in
FIG. 4
, the voltage-controlled oscillator
53
of a product may have the voltage-to-frequency characteristics indicated by broken line. In this instance, the free-running frequency is f
02
at the control voltage signal v
1
, and is different from the designed frequency f
01
. When the difference exceeds the control range of the loop consisting of the voltage-controlled oscillator
53
and the phase comparator
54
, the prior art automatic horizontal frequency regulation circuitry can not output any in-phase signal. In order to rescue the defective products from rejection, an external regulation circuit is required for the prior art automatic horizontal frequency regulation circuitry, and the manufacturer carries out the post regulation by using the external regulation circuit. The external regulation circuit makes the prior art synchronous signal processing circuit large, and increases the production cost thereof. Although discrete capacitors may avoid the problems, the semiconductor integrated circuit device requires additional pins to be connected to the discrete capacitors, and the discrete capacitors are not feasible.
SUMMARY OF THE INVENTION
It is therefore an important object of the present invention to provide an oscillation circuit, which automatically synchronizes an output oscillation signal with an input signal without any additional regulation circuit.
To accomplish the object, the present invention proposes to vary the control range of a voltage-controlled oscillator in the vicinity of the frequency of an input signal.
In accordance with one aspect of the present invention, there is provided a oscillating circuit for producing an output signal synchronous with an input signal comprising a signal input node supplied with the input signal, a voltage-controlled oscillator having voltage-to-frequency characteristics achieved in a certain control range and responsive to a control voltage signal for changing a frequency of the output signal, a first control loop connected to the signal input node and the voltage-controlled oscillator so as to compare the frequency of the output signal with an frequency of the input signal to see whether or not the input signal falls within the certain control range and changing a first sub-signal of the control signal so as to make the input signal fall within the certain control range when the input signal is out of the certain control range, and a second control loop connected to the signal input node and the voltage-controlled oscillator and controlling the voltage-controlled oscillator with a second sub-signal of the control signal so as to make the output signal and the input signal in-phase.
REFERENCES:
patent: 3825855 (1974-07-01), Basset et al.
patent: 5600279 (1997-02-01), Mori
patent: 5982208 (1999-11-01), Kokubo et al.
patent: 2-100348 (1990-08-01), None
patent: 3-274917 (1991-12-01), None
patent: 5-268078 (1993-10-01), None
patent: 9-246963 (1997-09-01), None
patent: 10-164395 (1998-06-01), None
Dickstein , Shapiro, Morin & Oshinsky, LLP
Mis David C.
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