JP2598926B2 - Color system conversion circuit - Google Patents

Description

The present invention relates to a method for converting a carrier signal into two-phase quadrature-modulated two color difference signals, for example, an NTSC signal and a PAL signal.

(B) Conventional technology The M system PAL color signal and the NTSC signal share the same horizontal synchronization frequency and vertical synchronization frequency, but differ in the frequency and phase of the color subcarrier. Therefore, in a video tape recorder to which an M-type PAL color television receiver is connected, it is necessary to convert an NTSC color signal into an M-type PAL color signal when reproduced. Conversely, when supplying an M-system PAL color signal reproduced by a video tape recorder to an NTSC color television receiver, the M-system PAL color signal must be converted to an NTSC color signal. Then, in the interchange between the M-system PAL color signal and the NTSC color signal, it is only necessary to convert only the modulated color signal.

On the other hand, when performing mutual conversion between a normal PAL color signal and an NTSC color signal, it is necessary to consider that the luminance signal is also different. However, if the conversion is performed on the modulated color signal, although the vertical direction of the screen is slightly expanded or contracted by performing the vertical synchronization adjustment of the television receiver, there is no practical problem.

Therefore, a circuit for inverting a burst signal by 90 ° and a circuit for forming a modulation color signal having an opposite phase to the modulation color signal are disclosed in Japanese Patent Application Laid-Open No. 58-161593 (H04N9 / 02). Some are provided with.

(C) Problems to be Solved by the Invention However, the conventional circuit described above requires a color subcarrier doubling circuit, a frequency conversion circuit, and a bandpass filter in order to form a modulated color signal of opposite phase.
It becomes difficult to make it into an IC.

(D) Means for Solving the Problems The present invention converts a color signal obtained by quadrature two-phase modulation of a carrier signal by two color difference signals into a zero signal of the carrier signal.
手段, 90 タ イ ミ ン グ, 180 ゜, 270 タ イ ミ ン グ timing sampling means, means for separating burst information and color information from the sampled output, and bursts of different types by at least multiplying the burst information by a predetermined value A burst forming means for converting information into information, and a method of distributing color information into two kinds of information of a first phase (90 °, 270 °) and a second phase (0 °, 180 °) and performing processing such as sign inversion. And a color forming means for converting the color information into color information.

(E) Function That is, in the present invention, a color signal of a certain color system is sampled at a predetermined timing, and the burst information and the color information are converted into burst information and color information of different systems, respectively.

(F) Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings. still,
The frequency of the color subcarrier has already been converted to the frequency of the format to be converted when it is reproduced and output from the video tape recorder. For this purpose, a frequency conversion circuit of a video tape recorder is used.

That is, in the video tape recorder, the modulated color signal is converted into a low frequency band and recorded, so that it is necessary to return the original band to the original band at the time of reproduction. Therefore, in the frequency conversion circuit for this purpose, the color subcarrier frequency of the system to be converted may be converted instead of the original color subcarrier frequency before recording.
(For example, when a PAL color signal is reproduced and supplied to a television receiver of an NTSC color signal, the output from the frequency conversion circuit is changed to the NTSC color subcarrier frequency.) For this purpose, the frequency of the carrier signal for frequency conversion supplied to the frequency conversion circuit may be made different from the normal case. First, an embodiment for converting from the NTSC system to the PAL system will be described.

First, the burst signal (BN) in the NTSC color signal is compared with the phase of the color subcarrier as shown in FIG.
There is a phase relationship of 0 °. On the other hand, the burst signal of the PAL color signal includes a delayed burst signal (BP1) of + 135 ° and an advanced burst signal (BP2) of -135 °. These burst signals are converted into color subcarrier phases 0 °, 90 °, 180 °, 2
When sampling at the timing of 70 °, the level becomes as shown in FIG. As is apparent from FIG. 3, in order to form a burst of the PAL color signal from a burst in the NTSC color signal, the level is set to 90 ° and 270 ° and the phase (the first phase). In the case of a delayed burst signal, the phase of 0 ° and 180 ° (second
Burst level 90 ゜ ahead in phase) Is delayed as it is by 90 °, and in the case of an advanced burst signal, it is necessary to further invert the sign of the 90 ° delayed output in the second phase.

 The modulated color signal E in the NTSC color signal is expressed as follows: E = (B−Y) sin ωt + (R−Y) cos ωt (1) (where ω = 2πfsc, fsc is a color carrier frequency).

 On the other hand, the modulated color signal E in the PAL color signal is represented by E = (BY) sinωt ± (RY) cosωt (2), and the sign is inverted every horizontal line.

As is clear from the equations (1) and (2), one of the modulated color signals (hereinafter, referred to as a fixed phase color signal) in the PAL color signal is common to the NTSC system, but the other modulated color signal (hereinafter, the inverted phase signal). 4, the level in the second phase must be opposite in polarity to that of the NTSC system, as apparent from FIG. That is, to form an inverted phase color signal, it is necessary to invert the sign of the sampling output of the second phase.

In view of the above, this embodiment is provided with a circuit block as shown in FIG.

First, an NTSC color signal is input to an AD conversion circuit (1) and an oscillation control circuit (2).

This oscillation control circuit (2) has a color subcarrier 4
The output of the oscillation circuit (21) that oscillates at twice the frequency is input to the 1/4 frequency divider (24), and the 1/4 frequency output obtained is used as the comparison input of the phase comparator (23). Is used as a reference input of the phase comparison circuit (23). The phase comparison circuit (23) performs a phase comparison using a burst gate pulse generated by a burst gate pulse generation circuit (22) for inputting a horizontal synchronization signal as a timing input, and controls the oscillation state of the oscillation circuit (21). ing. Further, this oscillation output is input to the sampling pulse generation circuit (25), and the color subcarriers 0 °, 90 °, 180 °, and 270 are output.
It is converted into a sampling pulse at the timing that matches the phase of ゜. Further, this sampling pulse is divided into a first phase pulse corresponding to a phase of 90 ° and 270 ° and a second phase pulse corresponding to a phase of 180 ° and 0 ° in a two-phase pulse generating circuit (26).

The AD conversion circuit (1) performs AD conversion in synchronization with the sampling clock. The AD conversion data is input to the data distribution circuit (3), and is divided into burst data and color data based on the burst gate pulse.

Burst forming means for inputting burst data (4)
First, burst data Input to the multiplication means (41). The multiplied data is input to one-clock delay means (42) for inputting a sampling pulse, and the multiplied data is delayed by one clock (90 °). The delayed data is further input to the first sign inverting means (43) and sign-inverted. The first data selecting means (44) has multiplied data as a first input and delayed data as a second input, and the second data selecting means (45) has multiplied data as a first input and inverted data as a second input. Both data selection means (44) and (45) select the first input by the first phase pulse and select the second input by the second phase pulse. As a result, delayed burst data is derived from the first data selecting means (44), and advanced burst data is derived from the second selecting means (45).

On the other hand, color forming means (5) for inputting color data
First, the color data is distributed and derived into the first phase data corresponding to the first phase pulse and the second phase data corresponding to the second phase pulse by the data distribution means (51). The first phase data is a first input of each of the third data selection means (53) and the fourth data selection means (54), and the second phase data is a second input of the third data selection means (53). . Further, the second phase data is sign-inverted by the second sign inversion means (54), and then becomes the second input of the fourth data selection means (53). The third and fourth data selection means (53) and (54) select the first phase data when the first phase pulse is input, and select the second phase data when the second phase pulse is input. As a result, the fixed phase color data which does not change the NTSC color signal is output from the third selection means, and the fourth data selection means (5
From (4), inverted phase color data in which the (RY) axis is inverted is derived.

The first input of the switching means (6) receives fixed phase color data corresponding to the delayed burst data as fixed phase data, and the second input receives advanced burst data and inverted phase color data as inverted phase data. Is done. The switching means (6) alternately selects an input in synchronization with a horizontal synchronization pulse to form PAL color data. The PAL color data is DA-converted in a DA conversion circuit (7) in synchronization with the sampling pulse. As a result, the NTSC color signal is converted into an M-type PAL color signal.

Next, an embodiment in which a PAL color signal is input and an NTSC color signal is output will be described with reference to FIGS.

In FIG. 5, the same components as those in FIG. 1 are denoted by the same reference numerals, and the detailed description is omitted. 1 includes an oscillation control circuit (2), a burst forming means (4),
The configuration of the color forming means (5) is slightly different, and a burst sequence generating means (8) is added.

First, the relationship between the burst signal of the PAL system and the NTSC system will be described with reference to FIG. Unlike the above-described case, when the average phase of the burst signals (BP ₁ ) and (BP ₂ ) of the PAL color signal is considered as a reference, the relationship is as shown in FIG. That is, the burst signal (BP ₁ ) in the PAL color signal
To form a burst signal of the NTSC color signal from (BP _2), the first phase (90 °, 270 °) the level of However, in the second phase (0 °, 180 °), it may be replaced with a fixed value of 0 (zero).

For the modulated color signal, the above equation (1) is used.
As is apparent from (2) and FIG. 7, the level of the second phase (0 °, 180 °) must be inverted in the inverted phase color signal.

Therefore, for the burst signal, the multiplication means (46) In the first phase (90 °, 270 °), the output of the multiplication means (46) is the first input and the fifth data selection means (47) having the fixed input of 0 (zero) as the second input. Select one input,
In the second phase (0 °, 180 °), by selecting the second input, the signal is converted into an NTSC burst signal.

The output of the data distribution circuit (3) is used as a first input of a switching circuit (6) on the one hand, and is input to the data distribution means (51) on the other hand. The data distribution means (51) distributes the first phase data and the second phase data according to the first phase pulse and the second phase pulse. Seventh data selection means (5
For (5), the first phase data is supplied as a first input, and the second phase data is inverted and supplied as a second input. Then, the data selecting means (55) in FIG. 7 selects the first input according to the first phase pulse and selects the second input according to the second phase pulse. The output of the seventh data selection means (55) becomes the second input of the switching means (6). On the other hand, the burst signal from the fifth data selection means (47) is applied to both inputs of the switching means (6).

The control of the switching means (6) is performed by the burst sequence generating means (8). The sixth data selection means (82) is selectively controlled by the output (0 °, 180 ° timing) of the two-phase pulse generation circuit (27) of the oscillation control circuit (2). That is, the first input (output of the data distribution circuit (3)) is applied to the output pulse of 0 °, and the second input (output of the data distribution circuit (3) is applied to the sign inversion circuit (81) for the output pulse of 180 °. ).

Therefore, the output of the sixth data selecting means (82) has a positive value in the horizontal period of the fixed phase color signal of the PAL color signal, and has a negative value in the horizontal period of the inverted phase color signal. In order to prevent malfunction, the output of the sixth data selection means (82) is averaged (integrated) and compared with a predetermined voltage (for example, a reference voltage (earth level)) (by the comparator (83)). The output of the comparator (83) becomes H level when the input is a positive value, and becomes L level when the input is a negative value.
It is provided to be a level. Then, the waveform of the comparator output (83) is further shaped by a pulse generating circuit (84) and applied to the switching means.

The switching means (6) is controlled to select the first input when the input PAL color signal is a fixed phase color signal, and to select the output of the color forming means (5) when the input PAL color signal is an inverted phase color signal. Thus, an NTSC color signal is obtained at the output of the D / A conversion circuit (7).

(G) Effects of the Invention As described above, according to the present invention, in the conversion between different color schemes, the doubling circuit of the color subcarrier, the frequency conversion circuit, and the band pulse filter are not required, and the IC conversion is realized. Is easy, and this effect is great.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram illustrating the phase relationship of the burst signal, FIG. 3 is a diagram illustrating the process of converting the burst signal, and FIG. 4 is a diagram illustrating the process of converting the color signal. 5 to 7 relate to the second embodiment, FIG. 5 is a circuit block diagram, FIG. 6 is an explanatory diagram of a conversion process of a burst signal, and FIG. 7 is an explanatory diagram of a conversion process of a color signal. FIG. (1) ... AD conversion circuit, (7) ... DA conversion circuit, (4)
... Burst conversion means, (5) color conversion means.

Claims (1)

(57) [Claims] A color signal obtained by orthogonally modulating a carrier signal with two color difference signals by two color difference signals is represented by 0 ° of the carrier signal,
Means for sampling at timings of 90 °, 180 °, and 270 °; means for separating burst information and color information from the output sampled by the sampling means; and different methods by multiplying the burst information by at least a predetermined number. A burst forming means for converting the color information into a first phase (90 °, 270 °) and a second phase (0 °);
{Circle around (180)}, and a color forming means for distributing the data into two types of data and converting the data into color information of a different type by sign inversion processing.