JPS6382084A - Oscillation system for highly stable reference frequency - Google Patents

Abstract

PURPOSE:To transmit a signal of highly stable and highly accurate frequency by providing a variable loop filter of the output of a phase comparing circuit, obtaining phase synchronism by a phase comparing circuit, and then adding band limitation to the variable loop filter and controlling a highly stable voltage- controlled oscillator. CONSTITUTION:The phase of a signal obtained through the 1/176 frequency dividion of a highly stable 10 MHz oscillator 9 is compared by a phase compar ing circuit 7 with the phase of a signal obtained by divding the frequency of the 3.58 MHz voltagecontrolled oscillator 5 by 63 and the loop filter 8 synchronizes the 3.58 MHz voltage-controlled oscillator 5 with the highly stable 10 MHz oscillator 10. The 3.58 MHz oscillator 5 is held highly stably. A phase comparing circuit 2 compares the phase of the output of the highly stabilized 3.58 MHz oscillator 5 with a color burst signal outputted by an extracting circuit 1. A lock detecting circuit 3 monitors the phase comparing circuit 2 and lowers the cutoff frequency of the variable loop filter 4 on detecting the acquisition of synchronism, thereby controlling the highly stable 10 MHz voltage- controlled oscillator 10 slowly.

Description

[Detailed Description of the Invention] [Summary] The present invention includes a circuit for extracting a color burst signal, a voltage controlled oscillator whose phase is synchronized with a highly stable voltage controlled oscillator,
It consists of a phase comparison circuit that compares the phase of the color burst signal and the output signal of the voltage controlled oscillator.The output of the phase comparison circuit is equipped with a variable loop filter, and after phase synchronization is achieved by the phase comparison circuit, the variable loop By adding a band limit to the filter and controlling the highly stable voltage controlled oscillator, it becomes possible to obtain a highly stable and highly accurate frequency.

[Industrial application field]

The present invention relates to a highly stable reference frequency oscillation method that oscillates a highly stable and highly accurate frequency using a color burst signal.

Currently, broadcasting stations generate color burst signals using highly stable and highly accurate atomic oscillators, that is, rubidium oscillators. On the other hand, on each receiving terminal side, a highly stable oscillator is required as a reference oscillation source for generating a carrier wave, for example, when performing bidirectional communication. From this point of view, a highly stable reference frequency oscillation method has been proposed that uses the highly accurate color burst signal to obtain stable subcarrier synchronized oscillation.

[Conventional technology]

A conventional subcarrier synchronized oscillator is configured as shown in FIG. 3. A color burst extraction circuit 1 that inputs, for example, a video signal sent from a television station; a color burst signal obtained from the color burst extraction circuit 1; and 3.
A first loop filter 8 includes a phase comparison circuit 2 that detects a phase difference with a subcarrier from a 58 MHz voltage controlled oscillator 5, and a loop filter 8 that applies a band limit to the phase difference obtained by the phase comparison circuit 2. A 1763 frequency divider 6 that divides the output of the automatic phase control circuit A, the signal obtained by the first automatic phase control circuit A, and the 10M1z voltage controlled oscillator 10, respectively.
and a second automatic phase control circuit B consisting of a 1/176 frequency divider 9, a phase comparator circuit 7, and a loop filter 11. Note that the 3.58 MHz voltage controlled oscillator 5 and the 10 MHz voltage controlled oscillator 10 use crystal oscillators.

[Problem that the invention seeks to solve]

In the conventional reference frequency oscillation method described above, the phase shifter is reduced by lowering the frequency of the loop filter, but narrowing the band narrows the variable range of the reference frequency obtained, resulting in a slow synchronization period and lack of stability. As a result, the frequency of the loop filter has to be increased, and as a result, the video jitter and noise jitter in the propagation path cannot be reduced, the phase jitter increases, and the noise/signal ratio increases, making it difficult to use as a reference frequency oscillator. There was a problem that it could not be used.

In view of the above-mentioned conventional situation, the present invention aims to provide a highly stable reference frequency oscillation method that can obtain a highly stable reference frequency that is unaffected by phase jitter occurring in the propagation path and phase jitter due to video signals. be.

[Means for solving problems]

In this invention, as shown in FIG. 1, an extraction circuit 1, a phase comparison circuit 2, 7, a 3.58 MHz voltage controlled oscillator 5, a frequency divider 6.9, a highly stable 10 MHz voltage controlled oscillator 10, and a lock detection circuit are used. 3, a variable loop filter 4, and a loop filter 8.

[Effect]

3.58 MHz voltage controlled oscillator 5 is highly stable 10 M
It is synchronized with the Hz voltage controlled oscillator 10 via the phase comparator circuit 7, resulting in a highly stable 3.58 MHz voltage controlled oscillator, and this is synchronized with the color burst signal. The lock detection circuit 3 detects that synchronization has been achieved, applies band limit to the variable loop filter, and controls the highly stable 10 MHz voltage controlled oscillator 10. Therefore, a highly stable reference frequency that is not affected by phase jitter can be obtained.

〔Example〕

FIG. 1 is a block diagram of an embodiment in which the present invention is applied;
A feature of the present invention lies in the use of a highly stable 10 MHz voltage controlled oscillator 10 which is extremely stable in the short term. The frequency fluctuation width of this highly stable 10 MHz voltage controlled oscillator 10 is about 2 cycles. In addition, this highly stable 10 MHz
The present invention is proposed from the viewpoint that the voltage controlled oscillator 10 needs to be controlled at a low frequency.

In other words, a highly stable 10 MHz oscillator 10 divided into 1/17B by the frequency divider 9, and a 3.58 MHz oscillator
The output of the z voltage controlled oscillator 5 is divided into 1/63 by the frequency divider 6.
A phase comparator circuit 7 compares the phases of the divided frequencies, and a loop filter 8 synchronizes the 3.58 MHz voltage controlled oscillator 5 with the highly stable 10 MHz oscillator 10. Therefore, the 3.58 MHz oscillator 5 can be kept highly stable.

The output of the highly stabilized 3.58 MHz oscillator 5 and the color burst signal output from the extraction circuit 1 for extracting the color burst signal are compared in phase by the phase comparison circuit 2.

When the lock detection circuit 3 monitors the phase comparator circuit 2 and detects that synchronization has been achieved, the lock detection circuit 3 lowers the cutoff frequency of the variable loop filter 4 and gently controls the highly stable 10 MHz voltage controlled oscillator 10.

If the phase comparison circuit 2 cannot be synchronized, for example, if the extraction circuit 1 does not extract a color burst signal, the lock detection circuit 3 detects an abnormality, and the variable loop filter 4 detects the abnormality.
The highly stable 10 MHz voltage controlled oscillator 10 oscillates at the self-oscillation frequency, and when the extraction circuit 1 extracts the color burst signal again, the synchronization control described above is performed.

〔effect〕

As is clear from the above description, according to the present invention, a highly stable reference frequency can be obtained without being affected by jitter, and if the present invention is applied to a device that requires a reference frequency, it will be extremely effective. be effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment to which the present invention is applied, and FIG. 2 is a block diagram of a conventional carrier synchronized oscillator.

Claims (1)

[Claims] An extraction circuit (1) for extracting a color burst signal, a voltage controlled oscillator (5) phase-locked to a highly stable voltage controlled oscillator (10), and a voltage controlled oscillator (5) that extracts the color burst signal and the voltage controlled oscillator (10). An automatic phase control system comprising a phase comparison circuit (2) that compares the phase with the output signal of step 5), and a variable loop filter (
4), and after the phase comparison circuit (2) achieves phase synchronization, the variable loop filter (4) applies band limitation to control the highly stable voltage controlled oscillator (10). Highly stable reference frequency oscillation method.