JPH0342782Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an automatic subcarrier switching circuit in a multi-system color television receiver.

In special regions such as the Middle East, due to historical background, the color television broadcasting system of developed countries, i.e.
PAL and SECAM systems are mixed, and
With the spread of VTRs, there is a demand for multi-system color television receivers that can not only receive broadcast programs from both of these formats, but also enjoy NTSC programs that are played back on VTRs from soft tapes provided by the United States, Japan, etc. In response to these circumstances, this type of multi-system color television receiver has been developed.

<Prior Art> In such conventional multi-system color television receivers, since the signal formats of the NTSC system and PAL system are generally relatively similar, the color signal processing circuits of both systems, especially the subcarrier oscillator, are It also uses a phase detector for APC, a phase detector for killer, etc., and determines the reception method at that time and performs appropriate switching operations accordingly.

To explain more specifically, the PAL system generally uses 4.43MHz as its subcarrier, whereas the NTSC system usually uses 3.58MHz. Also, in some areas it is 3.58M in PAL format.
Hz is also used in some places. Furthermore, NTSC
Also used as a subcarrier for VTR soft tapes using
There is a mixture of 3.58MHz and 4.43MHz.

Therefore, conventionally, multi-system color television receivers such as color television receivers capable of receiving both PAL and NTSC systems, and video tape recorders capable of playing various types of soft tape, usually use 4.43 MHz and 3.58 MHz. Two MHz subcarrier oscillators are used, and these two oscillators are switched in conjunction with system switching to obtain the required subcarrier output as appropriate.

For this reason, conventional multi-system color television receivers of this type use two oscillators, which increases costs and requires the output of these oscillators to be switched and driven each time according to each system.

Therefore, the applicant of the present application filed utility model registration application No. 51136 dated April 7, 1980 (see Utility Model Publication No. 152070/1983) as an improvement over such conventional technology.
For example, even when receiving color television signals of two or more systems with different subcarrier frequencies, such as PAL and NTSC, it is possible to obtain different subcarrier frequency outputs that match the systems from one oscillator. We have already proposed an automatic subcarrier switching circuit.

For example, this is configured as shown in FIG. 2, where 1 is a burst gate circuit that separates and derives only the burst signal component from the chroma signal based on the burst gate pulse of the horizontal scanning period, and 2 is the burst gate circuit that separates and derives only the burst signal component from the chroma signal. The phase detector for APC, 3 is a low-pass filter, and 4 is a VCO (voltage controlled oscillator). This VCO 4 constitutes an APC circuit together with the phase detector 2 and low-pass filter 3, and a subcarrier signal is oscillated from the VCO 4. .

Here, especially for this VCO4, one for 3.58MHz and one for 4.43M
Two Hz crystal oscillators 5a and 5b are attached,
A switching circuit 6 is inserted in series with these vibrators 5a, 5b, and these vibrators 5a, 5b are appropriately switched in accordance with the frequency of the burst signal.

Furthermore, here, 7 is a phase detector for killer use, and only when the regular output of this phase detector 7 stops, the flip-flop circuit 8 is invertedly driven based on a drive pulse of about 200 msec, and the switching circuit 6 is switched. .

To explain in detail the operation of the automatic subcarrier switching circuit configured as above,
When receiving NTSC color television broadcast,
A 3.58 MHz burst signal is separated and derived from the burst gate circuit 1 and supplied to each phase detector 2 and 7. At this time, the switching circuit 6 switches to the 3.58MHz crystal resonator 5a side according to the output of the flip-flop circuit 8, and also switches the APC
The loop is synchronized to 3.58MHz in accordance with the burst signal, and a 3.58MHz subcarrier signal is oscillated from VCO4. Once the APC loop is synchronized in this way, a detection output is derived from the phase detector 7, and based on this, the operation of the flip-flop circuit 8 is stopped from now on, and the normal signal is output from the VCO 4.
A stable subcarrier signal of 3.58MHz is oscillated.
However, for some reason, the flip-flop circuit 8
If the control of the APC is delayed and the switching circuit 6 is switched to the 4.43MHz crystal resonator 5b side, the APC
The synchronization within the loop is lost and no output is derived from the phase detector 7. At this time, the flip-flop circuit 8 is reversed by the next drive pulse, and the switching circuit 6 is switched to the 3.58 MHz crystal resonator 5a side. As a result, the APC loop is synchronized to 3.58MHz and a regular subcarrier signal of 3.58MHz is output from VCO4.

Similarly, when a PAL color television broadcast is received and a 4.43MHz burst signal is derived from the burst gate circuit 1, the switching circuit 6 switches the 4.43MHz crystal oscillator 5b based on the control output of the flip-flop circuit 8. switched to the side,
The APC loop is synchronized to 4.43MHz,
A 4.43MHz subcarrier signal is output from VCO4. Once synchronization is applied to 4.43MHz in the APC loop, a detection output is derived from the phase detector 7, after which the operation of the flip-flop circuit 8 is stopped, the switching circuit 6 is fixed to the 4.43MHz oscillator 5b side, and the output from the VCO 4 is A stable subcarrier signal of 4.43MHz is derived.

<Problem> By the way, in a multi-system color television receiver equipped with the above-mentioned automatic subcarrier switching circuit,
There was no problem when receiving PAL or NTSC signals, but there was a drawback that malfunctions occurred when receiving SECAM signals.

In other words, in the SECAM method, there is a
Contains a 4.25MHz or 4.406MHz subcarrier component,
Moreover, this frequency is very close to the frequency of the 4.43MHz burst signal, so when a SECAM format signal is received, the signal component applied to the trailing edge of the horizontal synchronization signal where the NTSC or PAL format burst signal is located. If this happens, there is a risk that the APC circuit will perform a pull-in operation, leading to an erroneous identification operation as if it had received a 4.43MHz burst signal.

<Purpose> The present invention was developed in view of the above points, and is applicable not only when receiving NTSC or PAL format on a multi-system color television receiver.
An object of the present invention is to provide an automatic subcarrier switching circuit that does not cause an erroneous identification operation even when SECAM format is received.

<Embodiment> An embodiment of the present invention shown in FIG. 1 will be described below. In FIG. 1, the same parts as in the conventional example shown in FIG. 2 are given the same reference numerals.

In this case, the conventional subcarrier automatic switching circuit shown in FIG. 2 is simply added with an OR gate circuit 9, and in this case, a flip-flop circuit 8
In addition to the output of , the color killer output obtained from the killer phase detector 10 built in the SECAM type color signal processing circuit is supplied to the switching circuit 6 via the OR gate circuit 9, and a The switching operation of the switching circuit 6 is performed by using the switching circuit 6.

Describing the operation of the automatic subcarrier switching circuit configured as described above, when an NTSC signal is received, the flip-flop circuit 8 goes high by an operation similar to that of the conventional example described above. The output is derived and applied to the switching circuit 6 via the OR gate circuit 9, and at this time the switching circuit 6 is switched to the 3.58 MHz crystal resonator 5a side. As a result, the APC loop is synchronized to 3.58MHz, and VCO4 is synchronized to 3.58MHz.
A stable subcarrier signal of 3.58MHz is output.

On the other hand, if a PAL signal is received,
An “L” output is derived from the flip-flop circuit 8, and at this time, an “L” output is derived from the OR gate circuit 9.
Since an output of Output.

However, when a SECAM system signal is received, an "H" output is derived from the killer phase detector 10 in the SECAM system color signal processing circuit, so the OR gate is output regardless of the output of the flip-flop circuit 8. 9, an "H" output is applied to the switching circuit 6, and at this time, the switching circuit 6 is switched to the 3.58 MHz crystal resonator 5a side. In this case, even if the 4.25MHz or 4.406MHz subcarrier component in the chroma signal is mixed into the APC phase detector 2, this is far different from 3.58MHz, so the APC loop will not perform a synchronization pull-in operation. VCO4 oscillates freely around 3.58MHz. At this time, a color killer output is derived from the killer phase detector 7, which stops the operation of the color signal processing circuit for the NTSC/PAL system, and only operates the color signal processing circuit for the SECAM system. The signal is received normally.

<Effects> As described above, according to the automatic subcarrier switching circuit of the present invention, in a multi-system color television receiver capable of receiving signals of the NTSC system, PAL system, and SECAM system, errors occur when receiving signals of the SECAM system. When receiving an NTSC/PAL signal, the content can be accurately identified without any identification operation, and a regular subcarrier signal matching each system can be appropriately oscillated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the automatic subcarrier switching circuit of the present invention, and FIG. 2 is a block diagram of a conventional automatic subcarrier switching circuit. 1...Burst gate circuit, 4...VCO, 5
a, 5b...Crystal resonator, 6...Switching circuit, 7...Killer phase detector, 8...Flip-flop circuit, 10...SECAM killer phase detector.

Claims (1)

[Scope of utility model registration request] In a multi-system color television receiver that can receive signals of PAL, SECAM, and NTSC systems, oscillators with different frequencies attached to a voltage-controlled oscillator (VCO) forming an APC loop are used. , a phase detector that detects the oscillation phase of the VCO and the phase of the burst signal, a flip-flop circuit whose operation is controlled based on the output of the phase detector, a SECAM killer phase detector, and the flip-flop circuit. An automatic subcarrier switching circuit comprising an OR gate circuit into which the output of the SECAM killer and the color killer output from the SECAM killer phase detector are input, and a switching circuit that appropriately switches the vibrator based on the output of the OR gate circuit. .