JPH048699Y2 - - Google Patents

Description

[Detailed explanation of the idea]

<Technical field> This invention can receive both PAL and NTSC color television broadcasts.
This invention relates to a vertical blanking pulse generation circuit in a PAL/NTSC shared receiver. <Background technology> Traditionally, in specific regions such as the Middle East,
A PAL/NTSC common TV receiver is used. Furthermore, recently, there are regions where VTR soft tapes include a mix of PAL and NTSC tapes, and even in these regions, PAL/NTSC shared receivers are used as monitor receivers. . By the way, the PAL system and the NTSC system differ as shown in Table 1, as an example of various constants related to horizontal and vertical scanning.

[Table] Therefore, in the conventional PAL/NTSC common receiver of this type, a relatively simple circuit as shown in FIG. 1 was used as the vertical blanking pulse generating circuit to generate the vertical blanking pulse. That is, in the vertical pulse amplifier 2 that amplifies the vertical oscillation signal obtained from the vertical oscillation circuit 1, an RC time constant circuit consisting of a resistor R ₁ , capacitors C ₁ , C ₂ and a transistor Q _{1 is attached, and the RC time constant circuit is attached to the vertical pulse amplifier 2 that amplifies the vertical oscillation signal obtained from the vertical oscillation circuit 1} .
By switching this RC time constant depending on the method reception, vertical blanking pulses with different pulse widths were obtained from the pulse amplifier 2. However, when the blanking pulse width is changed by switching the charging/discharging time constant of CR depending on the reception method as in the conventional circuit described above, the capacitors C ₁ and C ₂
Due to variations in the constants of the resistor R1 and the resistor _R1 , it was not possible to obtain the desired vertical blanking pulse width for each method, and therefore a vertical retrace line sometimes appeared on the screen. <Purpose> The present invention was devised in view of the above points, and provides a vertical blanking pulse generation circuit that can obtain a desired blanking pulse width with high precision in a PAL/NTSC common receiver. It is. <Example> An example of the present invention shown in FIG. 2 will be described below. Here, 3 is a synchronous separation circuit, 4 is a vertical oscillation circuit,
5 is a horizontal oscillation circuit, and each of these circuits 3, 4,
5 is not particularly different from those used in conventional PAL/NTSC joint receivers. Reference numeral 6 denotes a counter for determining the reception method, and this counter 6 counts the vertical synchronization signals obtained from the synchronization separation circuit 3, and in particular counts the number of synchronization signals that exist during a certain period of time. It is determined whether the signal is a NTSC format signal or an NTSC format signal. 7
is a horizontal counter, and this counter 7 is triggered by the vertical pulse obtained from the vertical oscillation circuit 4, starts counting the horizontal pulses obtained from the horizontal oscillation circuit 5, and generates a vertical blanking pulse having a predetermined pulse width. do. The set value of this counter 7 is appropriately switched according to the discrimination output of the reception method discrimination counter 6, that is, the reception method. If a PAL color television signal is currently being received, the vertical synchronization signal (50Hz) obtained from the synchronization separation circuit 3 is sent to the reception system discrimination counter 6.
When it is determined by counting that a PAL signal is being received, the set value of the horizontal counter 7 is set to 25, for example, based on the determination output of the counter 6 at this time. Therefore, in this case, the horizontal counter 7 is triggered every time a vertical pulse as shown in FIG. 3a is supplied from the vertical oscillation circuit 4, and counts the horizontal pulses as shown in FIG. 3b obtained from the horizontal oscillation circuit 5. Start. The horizontal counter 7 ends the counting operation every time 25 horizontal pulses are counted, and as a result, the counter 7 calculates a pulse width of 25H (where H represents the horizontal scanning period) as shown in Figure 3c. A rectangular wave pulse is output, which is amplified by a pulse amplifier 8 and then taken out as a vertical blanking pulse. However, when a color television signal of the NTSC system is received, the set value of the horizontal counter 7 is set to, for example, 14 based on the determination output of the reception system determination counter 6;
Then, each time the vertical pulse shown in FIG. 3a is supplied, the counting operation of horizontal pulses shown in FIG. 3b is triggered, and the counting operation is stopped every time 14 horizontal pulses are counted. As a result, the counter 7 outputs a rectangular wave pulse having a pulse width of 14H as shown in FIG. 3d, which is amplified by the pulse amplifier 8 and taken out as a vertical blanking pulse. In this way, in the vertical blanking pulse generation circuit of this embodiment, as described above, the receiving system determining counter 6 determines whether the signal currently being received is the PAL system or the NTSC system, and based on the output of this determination. The set value of the horizontal counter 7 is automatically switched and set, and as a result, the horizontal counter 7
A vertical blanking pulse having a pulse width of 25H when receiving the PAL system and 14H when receiving the NTSC system is output. <Effects> As described above, the present invention has a reception method discriminating means that counts the number of vertical synchronization signals present during a certain period of time and determines whether the reception state is PAL or NTSC. , the horizontal oscillation signal is counted triggered by the vertical oscillation signal, and the count setting value is determined to be a value corresponding to the vertical blanking pulse width of the PAL system or a vertical blanking pulse of the NTSC system based on the determination output of the reception system determining means. It is equipped with a horizontal counting means that can be switched to a value corresponding to the width, and is characterized by obtaining a vertical blanking pulse with a pulse width corresponding to the PAL system or NTSC system depending on the reception condition, so it is always responsive to each reception system. A blanking pulse having a predetermined pulse width can be obtained. Therefore, the vertical blanking pulse generation circuit of the present invention
If used in a PAL/NTSC shared receiver, vertical retrace lines will no longer appear on the screen as in the past.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a vertical blanking pulse generation circuit used in a conventional PAL/NTSC shared receiver, Fig. 2 is a block diagram of one embodiment of the present invention, and Fig. 3 is a block diagram of the same embodiment. FIG. 3 is a signal waveform diagram for explaining operation. 3... Synchronous separation circuit, 4... Vertical oscillation circuit, 5
...Horizontal oscillation circuit, 6...Counter for determining reception method, 7...Horizontal counter, 8...Blanking pulse amplifier.

Claims (1)

[Claims for Utility Model Registration] Receiving method determining means for counting the number of vertical synchronization signals present during a certain period of time to determine whether the receiving state is PAL or NTSC, and vertical oscillation. The horizontal oscillation signal is counted triggered by the signal, and the count setting value is set to a value corresponding to the vertical blanking pulse width of the PAL system or a value corresponding to the vertical blanking pulse width of the PAL system or NTSC based on the determination output of the reception system determination means.
A vertical blanking method is provided with a horizontal counting means that can be switched to a value corresponding to the vertical blanking pulse width of the PAL system or the NTSC system, and obtains a vertical blanking pulse with a pulse width compatible with the PAL system or the NTSC system depending on the reception state. Ranking pulse generation circuit.