JPS60235598A - Vco for secam encoder - Google Patents

Abstract

PURPOSE:To attain circuit integration by matching focibly an oscillating frequency of a VCO from the start time of subcarrier blanking till the start time of a composite synchronizing signal to a reference frequency so as to lock surely the oscillating frequency to the reference frequency even in a short phase locked time and use only one VCO. CONSTITUTION:A trigger circuit 30 is added to a VCO main body 10 and a phase comparator 20, a switch SW2 is closed in the timing shown in Fig. (d) so as to control each function activated respectively. That is, the VCO main body 10 is triggered in the reference frequency by the timing when the switch SW1 is closed and the PLL lock is attained at the remaining time. In this case, the phase comparator 20 applied PLL operation when the power switch SW2 is closed and holds the control variable of feedback when the SW2 is opened. Thus, the phase lock is attained surely in a short time, stable operation is attained, one VCO main body and one phase comparator are enough for the circuit operation and monolithic circuit integration is realized.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention provides a
It is related to CO.

[Prior art] Generally, the color signal in the SECAM color TV signal is FM
Using a modulated signal, the reference frequency is 282 f H (4,40625 MH) per horizontal scanning (H) time.
z) and 272 f H (4.25 MHz). Therefore, two COs for the conventional SECUM encoder are prepared, one for 282fH and one for 272fH, and their outputs are switched and used for each IH, and the VCO that is not at output time is activated by PLL operation during the IH waiting time. , was configured to lock to a reference frequency.

However, this conventional configuration has drawbacks such as the need for two VCOs and the need to take countermeasures against beats due to the fact that the frequencies of the two VCOs are adjacent to each other.

Also, in order to convert the SECAM encoder system into an IC, V
It is necessary to configure it with one CO, but in order to use one VCO, the time allowed for locking to the reference frequency by PLL operation becomes extremely short. Therefore, in order to obtain stable operation, it is necessary to add a very complicated circuit such as the addition of a VCO operation stop circuit, and it has been difficult to implement this into an IC.

[Summary of the invention]

The present invention was made in view of the above-mentioned situation, and includes a method of forcing the oscillation frequency of the VCO to match the reference frequency from the start time of subcarrier blanking to the start time of the composite synchronization signal. By stabilizing the oscillation frequency by phase locking from the start time of the composite synchronization signal to the end time of subcarrier blanking, it is possible to construct a SECUM encoder system that can operate stably with three V2O units, and also to integrate it into an IC. The purpose is to provide a ■CO for SECUM encoders that can be achieved.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 shows a SECOM encoder according to an embodiment of the present invention.
In the figure, 10 is the VCO main body, and the
The main body 10 is of a conventionally known delayed multi-type system, and its oscillation frequency is controlled by the voltage difference between the reference human power Vref and the control human power Vc. Also VCO
A phase comparator 20 is provided as a feed bank circuit to match the oscillation frequency of the main body 1o with the frequency of the reference signal a, and the phase comparator 20 is configured to match the frequency of the output signal A of the VCO main body 10 and the frequency of the reference signal a. The comparison result is fed back to the operating current of the VCO main body, and V
The CO reference oscillation frequency is determined. When the phase comparator 2o operates, the control human power Vc of the VCO main body 10 is set to the same potential as the reference human power Vref.

In the conventional SECUM encoder system, two sets of this VCO and a phase comparator were prepared. Then, switch SW2, which controls the timing at which the phase comparator operates, is closed every IH to adjust the VCO to the reference frequency, and when it is open, only Vco is operated, and the operation timings of the two sets are set to IH.
By shifting the outputs by H and selecting and using the outputs of the two VCOs alternately, a continuous ■CO output was obtained. In contrast, in this embodiment, a trigger circuit 30 is added to the VCO main body IO and the phase comparator 20, and the switch SW2 is closed at the timing Tdl in FIG. 2 to control each function to operate. The number of phase comparators has been reduced.

By the way, the time required for the output b of the VCo body 1o to be a TV video signal is outside the subcarrier blanking period as shown in FIG.
To configure a CO-only SECAM encoder system,
It is necessary to lock the oscillation frequency of the VCO main body 1o to the frequency of the reference signal a using this blanking period BL (see figure (al)). However, since this time is short, it is not possible to reliably use only P and LL operations. Can't get it to lock.

Therefore, in this embodiment, as shown in FIG. 2 (cl), the CO main body 10 is triggered at the reference frequency only when the switch SWI is closed, and the lock is performed by PLL operation during the remaining time. In this case, the phase comparator 2o is activated by the PLL when its power switch SW2 is closed.
When the switch SW2 is opened, a hold operation is performed to bold the control amount of the feed bank.

In this way, in this embodiment, the oscillation frequency of the CO main body is forced to match the reference frequency at the start of the subcarrier blanking time, so phase lock can be achieved reliably in a short time and stable operation can be achieved. It was possible, and only one VCO body and one phase comparator were required, making it possible to create a monolithic IC.

Also, since only one CO body is required, there is no variation in characteristics and there are no problems such as beats.

[Effects of the Invention] As described above, the ■CO for SECUM encoder according to the present invention
According to the method, the oscillation frequency of the VCO is forced to match the reference frequency from the start time of subcarrier blanking to the start time of the composite synchronization signal, and the oscillation frequency of the VCO is forced to match the reference frequency from the start time of the composite synchronization signal to the start time of the composite synchronization signal. Since the oscillation frequency is stabilized by phase lock until the end time, the oscillation frequency can be reliably locked to the reference frequency even with a short phase lock time, and as a result, the VCO is 1.
This has the effect of making it possible to achieve IC implementation.

[Brief explanation of the drawing]

FIG. 1 shows a V for a SECUM encoder according to an embodiment of the present invention.
The circuit diagram of the CO, FIG. 2, is a diagram showing the operation timing of the circuit of FIG. 1. 10... ■CO main body, 20... Phase comparator, 30.
...Trigger circuit. Agent Masuo Oiwa Figure 1 (272fHor 282fH)

Claims (1)

[Claims] (1) The main body of the CO that oscillates at one of two reference frequencies, and the sub The above VC operates from the start time of the carrier blanking period to the start time of the seven-cam composite synchronization signal.
a trigger circuit that matches the oscillation frequency of the VCO main body with the frequency of the reference signal; and a trigger circuit that operates from the start time of the composite synchronization signal to the end time of the subcarrier blanking period to connect the output of the VCO main body and the reference signal. A VCO for a SECUM encoder characterized by comprising a phase comparator that compares phases and feeds the comparison results to the vCO main body.