JPS6247389B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention aims to simplify the circuit configuration by making it possible to share the main parts of an NTSC system synchronization signal generator and a so-called PAL-M system synchronization signal generator.
This paper proposes a synchronization signal generator for NTSC and PAL-M systems. In the PAL-M system, the horizontal sync frequency _H and vertical sync frequency _V are equal to the horizontal sync frequency and vertical sync frequency of the NTSC system,
Refers to a PAL system in which the color subcarrier frequency _C has the relationship _C = 909 _H/4 .

An example of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a system diagram of an example of the present invention, where 1N is the original oscillator used in the NTSC system, and the original oscillation frequency is the color subcarrier frequency.
It is selected to be four times as large as _C (=910 _H ). on the other hand,
(1P) is the original oscillator of the PAL-M system, and the original oscillation frequency in this case is selected to be four times the color subcarrier frequency _C (=909 _H ). These original oscillation outputs are frequency-divided into 1/4 by a frequency-dividing counter 2 to form color subcarrier signals S _C suitable for each standard system.

10 is a synthesizer, in the case of NTSC system and
It is used in both cases of PAL-M system. The reference frequency o used in this synthesizer 10 is
In order to achieve zero sharing, the original oscillation frequency of the NTSC system is especially used. From this synthesizer 10, in this embodiment, a horizontal period signal S
_H , a vertical period signal S _V and a color framing signal C _F as a field identification signal are formed.

Therefore, as shown in the figure, the reference signal S _O is supplied to the counter 11 and the reference frequency _O is divided by 1/455 to form a signal S _2H that is twice the horizontal synchronization frequency _H , which is further sent to the counter 12. The frequency is divided by 1/2 to form a horizontally periodic signal S _H . signal S _2
H is further divided into 1/525 by a counter 13, thereby forming a vertical period signal S _V.

Note that the signal S _V of this vertical synchronization frequency _V is 1/4
is supplied to a logic circuit 14 having a counter of 4 to form a field signal C _FN with a 4-field period, and this is further supplied to a 1/2 counter 15 to form a field signal C _FP of 8 field periods.
is formed.

Here, in the case of the NTSC system, the color subcarrier signal S _C
The field period in which the phase of returns to the original value is 4 fields, and in the case of the PAL-M method, it is 8 fields, so the relative phase between the above-mentioned field signals C _FN , C _FP and the color subcarrier signal S _C is always fixed. If the relationship is as follows, these field signals C _FN and C _FP
can be used as a color framing signal in each standard system.

The means for specifying the relative phase will be explained from the case of the NTSC system.If the counting state of the counter 2 for forming the color subcarrier signal is controlled (reset, loaded, etc.) by the field signal C _FN , this field signal C _FN Since the phase of the color subcarrier signal S _C is regulated by , the relative phase is fixed thereby. In this example, the control signal for counter 2 is not the field signal C _FN itself, but
A signal with a horizontal period of 2m (m is an integer) is used.
That is, if the horizontal period is used as a reference, the phase of the color subcarrier signal S _C returns to its original state every two horizontal periods, so it is sufficient to control the counter 2 with a signal of this 2 m horizontal period.

In this example, even in the case of m=1, the control signal S〓 _H is formed by the 1/2 counter 16, which is supplied to the counter 2, and the control signal S〓 _H of two horizontal periods is used to generate the color. The phase of the subcarrier signal S _C is regulated. Then, the logic circuit 14 is further controlled (in this example, reset) by this control signal _S〓H , and as a result, the phase of the field signal _CFN is regulated by _the control signal _S〓H . The relative phase of the subcarrier signal S _C is fixed by this control signal S 〓 _H , and this field signal C _FN becomes a color framing signal.

By the way, the count phase of counter 2 can also be controlled by using the control signal S 〓 _H itself, but in this example, for the reasons described below, this control signal S 〓 _H is temporarily output from the original oscillation. This is a case where the output normalized to S _N is used as a control signal.

That is, since a large number of counters are used to obtain the horizontal period signal _S from the original oscillation output _S In this case, the count phase is controlled when the control signal is "1" or "0", so if the pulse width of this control signal is one clock width or more of the original oscillation output S _N , the pulse width The count phase controlled by the difference in , will also vary.

Therefore, due to these reasons, there is a possibility that the count phase controlled by the control signal S– _H cannot always be fixed. In this embodiment, such unstable elements of counter control are removed by normalizing them to the original oscillation output S _N .

FIG. 2 shows an example of the normalization circuit 20, which is composed of two D-type flip-flop circuits 21 and 22, with a signal S _H supplied to each clear terminal, and an original oscillation output S _N supplied to the clock terminal. A certain reference signal S _O is provided. Since the DC voltage B ₊ is applied to the _D1 terminal of the flip _- flop circuit 21 in the previous stage, _the signal _S〓H (in the figure B), the output of the _Q1 terminal S _q1 occurs at the rising edge of the reference signal S _O immediately after the input of this signal S 〓 _H.
stands up as shown in the figure. The inverted output _q1 (D in the same figure) is supplied to the _D2 terminal of the flip-flop circuit 22 in the subsequent stage, so the output _Sq2 of the _Q2 terminal is one cycle of the reference signal _SO immediately after the input of the signal _S〓H . It is synchronized with the rising edge and is obtained only during this one cycle (E in the same figure), and based on the signal _S
The reference signal S _O of _C is standardized.

This normalized output S _q2 has a pulse width within one cycle of the reference signal S _O. Therefore, if the counter 2 is controlled by this normalized output S _q2 , the phase relationship between the color framing signal C _FN and the color subcarrier signal S _C will always be constant.

By the way, in the case of the NTSC system, the original oscillation frequency is 910 _H , which is the same as the reference frequency _O , so
When the circuit shown in FIG. 1 is used as an NTSC synchronization signal generator, the original oscillation output S _N may be directly supplied to the synthesizer 10. In contrast, in the case of the PAL-M method, the original oscillation frequency is 909
_Therefore , when this circuit is used as a PAL-M synchronizing signal generator, the original oscillation output S _P cannot be directly used as the reference signal S _O.

Therefore, in this invention, a variable oscillator is provided, and the 910 _H oscillation output (phase-locked to the original oscillation output S _P ) obtained by this variable oscillator is used as the reference signal S _O
30 indicates a voltage controlled variable oscillator (VCO).

The first and second switches SW ₁ and SW ₂ are switched as shown by the broken line, and the original oscillation output S _P is switched as shown by the broken line.
The signal is supplied to the counter 31 via SW ₁ and frequency-divided to 1/909 to form a horizontal period signal S _H .

On the other hand, the oscillation output obtained by the VCO 30 is sent to the counter ₁₁ via the second switch SW2 as the reference signal S.
As _a result, in the case of the PAL-M system as well as in the case of the NTSC system, a signal S _H with a horizontal period is obtained at the terminal 12a, and a signal S _V with a vertical period is obtained at the terminal 13a. The horizontal period signal S _H 〓 described above is then supplied to the phase comparator 32 together with the horizontal period signal S _H obtained from the counter 12 for phase comparison, and its output is passed through the low pass filter 33 to the VCO 30 to control its control. Supplied as voltage. Because the existence of this PLL system makes the phases of the signals S _H and S _H 〓 match,
The oscillation output of the VCO 30 can be used as a reference signal S _O for the synthesizer 10, and as a result, the synthesizer 10 can also be used as a synthesizer for a PAL-M synchronization signal generator.

Next, we will discuss color framing in the PAL-M system. In this example, the frequency-divided output _S〓V of 8 field periods, which is frequency-divided by the counter 35 to 1/2100, is used as a control signal for the counter 2. In this case as well, the counter 2 is controlled by an output obtained by normalizing the frequency-divided output _S〓V to the original oscillation output power _SP . 40 is a standardization circuit, and its configuration and operation description will be omitted. The third switch _SW3 is switched as shown by the broken line.

This frequency divided output _S〓V used as a control signal for the counter 2 is further supplied as a control signal (set pulse or reset pulse) to the counters 13, 15 and the counter of the logic circuit 14. In this way, if the count phase of the counter 2 for forming the color subcarrier signal, the counters 13 and 15 for forming the field signal, and the counter of the logic circuit 14 are simultaneously controlled by the divided output S〓 _V , the color subcarrier signal S Since the relative phase of _C and field signal C _FP is fixed, field signal C _FP is
It can be used as a color framing signal in the PAL-M system.

Note that the horizontal period signal S _H , vertical period signal S _V , color framing signal C _F and color subcarrier signal S _C obtained by the synthesizer 10 are supplied to a synchronization signal synthesizer (not particularly shown). From this, various synchronization signals required in television systems, VTR systems, etc., such as horizontal and vertical synchronization pulses, horizontal and vertical drive pulses, and color framing signals used in editing, multiple relay, etc. It is something that is formed.

As explained above, according to the present invention, the synthesizer 10, which is the main part of the synchronous signal generator, can be used in common in the NTSC system and PAL-M system synchronous signal generator, so that the circuit configuration can be simplified. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an example of the present invention, FIG. 2 is a connection diagram showing an example of a standardization circuit, and FIG. 3 is a waveform diagram for explaining its operation. 1P and 1N are the original oscillators, 10 is the synthesizer,
20 and 40 are standardization circuits, and 30 is a VCO.

Claims (1)

[Claims] 1. An 11th source oscillator that oscillates a frequency that is an integral multiple of the color subcarrier frequency in the NTSC system, and a PAL
- a second source oscillator that oscillates a frequency that is an integral multiple of the color subcarrier frequency in the M method; a synthesizer that divides the input reference signal to obtain at least a horizontal period signal and a vertical period signal; It has a variable oscillator that oscillates at substantially the same frequency as the oscillation frequency of the original oscillator, and in the case of the NTSC system, the oscillation output of the first original oscillator is supplied to the synthesizer as an input reference signal via a switch, In the case of the PAL-M system, the oscillation output of the variable oscillator is supplied to the synthesizer as an input reference signal via the switch, and the horizontal period obtained by frequency-dividing the oscillation output of the second original oscillator. The variable oscillator is controlled by the output of a phase comparison between the signal and the horizontal period signal obtained from the synthesizer, and the switch is configured to switch between the NTSC system and the PAL-M system. .