JPS61277273A - Video signal generator - Google Patents

Abstract

PURPOSE:To generate a horizontal synchronizing signal both the M-NTSC and B-PAL systems with low cost and high accuracy with simple circuit constitution by providing a single crystal oscillator sending a reference horizontal frequency signal and a frequency divider applying frequency division to this signal with a prescribed frequency division rate. CONSTITUTION:When N1=1001 is selected as a setting value for a selection circuit 15C, the count of a counter 15a is 1001, a coincidence pulse is sent from a comparator 15b, the counter 15a is reset and starts counting again. Since the coincidence pulse is sent every time the count reaches 1001, the coincidence signal becomes the horizontal synchronizing signal of the M-NTSC system where the reference horizontal frequency from a crystal oscillator 14 given as the count clock is subjected to frequency division by a frequency dividing ratio of 1/1001. Similarly, when the B-PAL count value N2 is selected based on the selection signal 16, the reference horizontal frequency and the B-PAL system horizontal synchronizing signal subjected to frequency division of 1/1008 are sent from the comparator 15b. Thus, high reliability and accuracy are attained with simple circuit constitution and low cost.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal generator that outputs a video signal, etc. to a display device such as a CRT, and particularly relates to a horizontal synchronization signal for outputting a video signal, etc. This relates to a configuration that generates .

[Prior art] Conventionally, the television standard system M-NTSC (M-Natio
na1choelevision System Comm
1ttee) system and B-PAL (B-P
In the case where the reference frequency of the horizontal frequency of the (hase Alternation Line) method is switched and generated, there is a configuration shown in FIG. 4 or FIG. 5, for example.

In FIG. 4, (1a) is a crystal oscillator that sends out a frequency signal L times the horizontal frequency of the N-NTSC system, (2a)
) is a frequency divider with a frequency division ratio of 1/L, (3a) is a III-NT
This is the horizontal frequency of the SC system. Similarly, (lb) is B
- A crystal oscillator that sends out a frequency signal M times the horizontal frequency of the PAL system, (2b) a frequency divider with a frequency division ratio of 1/M,
(3b)' is the horizontal frequency of the B-PAL system, and the horizontal frequency (8) selected by the selector (4) with the selection signal (5) is output as the horizontal frequency of the M-NTSC system and the B-PAL system. It is made to be. However, N
is an integer.

In addition, in FIG. 5, (7) is the reference crystal oscillator, (8
) is a phase comparator, (9) is an integrator, (10) is a voltage controlled oscillator, (lla) and (llb) are frequency dividers with variable division ratios, forming a phase-locked loop, and the frequency divider ( lla
) and (llb) are selected by the selection signal (12), and the selected horizontal frequency is the output signal (13).
).

[Problems to be Solved by the Invention] However, in the conventional device having the configuration shown in FIG. 4, a plurality of crystal oscillators must be used, which is expensive.
Further, the configuration shown in FIG. 5 has a problem in that the circuit configuration is complicated and there are many adjustment elements.

This invention was made to solve the above-mentioned problems, and provides an inexpensive and highly accurate M-NTSC with a simple circuit configuration using a single crystal oscillator.

It is an object of the present invention to provide a video signal generator capable of generating both B-PAL horizontal synchronization signals.

[Means for Solving the Problems] A video signal generator according to the present invention includes a single crystal oscillator that sends out a reference horizontal frequency signal of a predetermined frequency, and a frequency division ratio of 1 that is switchable based on a switching selection signal. The present invention includes a frequency divider that divides the reference horizontal frequency signal at a predetermined frequency division rate, and generates a horizontal synchronization signal that is compatible with a plurality of systems.

[Function] The video signal generator of the present invention can easily select a horizontal synchronizing signal that is compatible with multiple systems by changing a single reference horizontal frequency signal by a predetermined frequency division ratio, and the selection can be done by adjusting the horizontal synchronizing signal. can be made unnecessary.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
In the figure, (14) is a crystal oscillator that sends out a reference horizontal frequency signal of 15.75 MH2, and (15) is a frequency division ratio of 171001 and 1/1008 according to the switching selection signal (1B).
The horizontal synchronizing signal of either M-NTSC or B-PAL is selected and outputted as the output signal (17) by the selection signal.

That is, when the M-NTSC system is selected by the selection signal (1B), the frequency division ratio of the frequency divider (15) is 1/100.
1, and the output (17) becomes a horizontal opening signal of 15734.2115 Hz. This frequency is M-NTSC
Horizontal frequency of the method: 15734.28Hz±0.0000
It is within the tolerance of 1%.

On the other hand, when the B-PAL system is selected by the 1 selection value number (1B), the frequency division ratio of the frequency divider (15) becomes 1/1008, and the output (17) becomes 15825.0 Hz. This frequency is the horizontal frequency of 15825Hz in B-PAL system.
It is within the tolerance range of ±0.00001%.

In addition, Fig. 2 and Fig. 3 respectively show the above selection signal (1B).
A frequency divider (15) that changes the frequency division ratio based on the frequency and sends a horizontal synchronizing signal of either M-NTSC or B-PAL system.
In Fig. 2, (15a
) is the above crystal oscillation! 15.7 sent from (14)
A counter (15b) that inputs and counts a 5MHz reference horizontal frequency signal as a count clock is a comparator that sends out a coincidence pulse when the count number of the counter (15a) reaches a predetermined value. ) and as a reset input to the M-NTSC or B-PA as described below.
This is one of the horizontal synchronization signals of the L system.

Therefore, (15c) is M based on the selection signal (IB).
- A selection circuit that selects either the NTSC count value Nl (Ml-1001) or the B-PAL count value N2 (N2-1008) and sends it to the comparator (15b) as a comparison setting value, for example N1-1001. is selected as the set value, when the count value of the counter (15a) reaches 1001, the comparator (15b)
A coincidence pulse is sent out from the counter (15a), and the counter (15a) is reset and starts counting again.A coincidence pulse is sent out every time the count value reaches 1001, so the coincidence pulse is given as a count clock. 15 which is obtained by dividing the standard horizontal frequency 15.75MH2 from the crystal oscillator (14) with a frequency division ratio of 1/1001.
This is a 734.28 Hz M-NTSC horizontal synchronization signal.

Similarly, when the B-PAL count value N2 is selected based on the selection signal (16), the comparator (tsb
), the reference horizontal frequency is 15.75MHz and the frequency division ratio is 1/
15B25 divided by 1008. oOH2 B-PAL
The horizontal synchronization signal of the system will be sent out.

In contrast to the embodiment shown in Fig. 2 above, the structure shown in Fig. 3 has a frequency divider (
This is a configuration example according to another embodiment of 15), and in the figure, (1
5d) is a counter whose initial value to be loaded changes based on the selection signal (1B); for example, this counter (15d)
When the maximum count-up value is 2000, the M-NTSC count value N1 selected by the 1 selection circuit (15c) is set to 988, and the B-PAL count value N2 is set to 882. Therefore, for example, when the selection circuit (15c) selects the NTSC count value Ml (Ml-999) based on the selection signal (1B), the counter (15d) starts loading from the initial value 888 and uses the crystal oscillator. (Reference horizontal frequency from 10 (
15.75MHz) as a count clock and count until the count value reaches 2000.
A carry output is sent in 001 cycles. In other words, M-N of 15734.26Hz, which is obtained by dividing the reference horizontal frequency (15.75MHz) with a frequency division ratio of 1/1001.
The TSC horizontal synchronization signal is sent out as a carry output. Similarly, when the selection circuit (15c) selects the count value N2 (N2-992) as the initial value to the counter (15d), the reference horizontal frequency 15.75MH2 is divided into 1/1008 as a carry output. A frequency-divided 15825.00 Hz B-PAL horizontal synchronization signal is sent out.

In the above embodiment, it goes without saying that the original oscillation frequency and frequency division ratio may be multiplied by the same integral number.

[Effects of the Invention] As described above, according to the present invention, since a single crystal oscillator is used and the circuit configuration is simple, the device can be made at low cost, and
Since no adjustment is required and it is easy to configure with a highly stable circuit, it has the effect of obtaining high reliability and accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the present invention, FIG. 2 is a detailed internal block diagram of the frequency divider shown in FIG. 1, and FIG. 3 is a diagram of a frequency divider according to another embodiment corresponding to FIG. The detailed internal configuration diagrams of FIGS. 4 and 5 are conventional configuration diagrams that are compatible with both M-NTSC and B-PAL systems, respectively. In the figure, (14) is a crystal oscillator, (15) is a frequency divider, (15a
) is a counter, (15b) is a comparator, (15c
) is a selection circuit, (15d) is a counter, (te) is a switching selection signal, and (17) is a horizontal synchronization signal. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) A video signal that generates a horizontal synchronizing signal of the M-NTSC system, B-PAL system, or a standard system with a horizontal frequency similar to these among the television standard systems to output a video signal etc. to a display device. a single crystal oscillator for delivering a reference horizontal frequency signal at a predetermined frequency in the generator;
and a frequency divider whose frequency division ratio is switchable and which divides the reference horizontal frequency signal by a predetermined frequency division ratio based on a switching selection signal, and generates a horizontal synchronization signal compatible with a plurality of systems. video signal generator. (2) The frequency divider includes a counter that inputs and counts the reference horizontal frequency sent out from the crystal oscillator as a count clock, and a comparator that sends out a matching pulse when the count number of this counter reaches a predetermined value. , a selection circuit that selects one of the plurality of setting values based on the switching selection signal and sends it to the comparator as a comparison setting value, and provides the matching pulse as a reset input to the counter, The video signal generator according to claim 1, characterized in that the video signal generator is configured to generate a horizontal synchronization signal. (3) The frequency divider inputs the reference horizontal frequency sent from the crystal oscillator as a count clock, and also connects the counter to which the initial value to be loaded is set and counts up to the maximum count-up value, and the switching selection signal. a selection circuit that selects one of a plurality of set values based on a plurality of set values and changes the initial value to be loaded into the counter, and provides a carry output sent from the counter as a load pulse input, and a horizontal synchronization signal. 2. A video signal generator according to claim 1, characterized in that the video signal generator has a configuration as follows.