JP2594153B2 - MUSE / NTSC converter - Google Patents

Description

The present invention relates to a MUSE / NTSC converter, and more particularly to a color subcarrier signal generation technique for a color encoder.

(B) Conventional technology Multiple Sub-Nyquist Sampling (MUSE) is used as a method for transmitting high-definition video signals through band compression using broadcast satellites.
Encoding) has been proposed by NHK and is being broadcast on NHK satellite channel 2 (BS channel 11).

This method uses a single channel of satellite broadcasting (bandwidth 27
In order to transmit a high-definition video signal at the same frequency, a sub-Nyquist sampling is performed on the high-definition video signal using a band compression encoder, and a band-compressed video signal (MU
SE signal, sub-sampled video signal).

The MUSE method is introduced in the following documents and the like.

(A) NHK Technical Research Vol. 39 No. 2 No. 172 of 1987,
18 (76)-53 (111), Ninomiya, Otsuka, Izumi, Koshi,
"Development of MUSE method" by Iwadate.

(B) Magazine "Nikkei Electronics, Nov. 2, 1987, No. 433", published by Nikkei McGraw-Hill, pp. 189-212, by Ninomiya, "Transmission system MUSE for high-definition broadcasting using satellites."

In order to view an image of this MUSE signal (see FIG. 5) on a current television receiver (TV), a MUSE having 1125 scanning lines is required.
A MUSE / NTSC converter for converting the signal into an NTSC signal of 525 scanning lines is required.

As the MUSE / NTSC converter, for example, a prototype MUSE / NTSC converter “UC-2” manufactured by Mitsubishi Electric Corporation is known.

This MUSE / NTSC converter (hereinafter, referred to as a converter) is used to display a MUSE playback screen having an aspect ratio of 16: 9 shown in FIG. 6a on a normal TV having an aspect ratio of 4: 3. Is the “wide mode” of FIG.
The “zoom-up mode” in FIG. C can be selected.

Other than the above, the image modes include “zoom-up mode right” and “left” as shown in FIGS. 6d and 6e, “horizontal compression mode” as shown in FIG. 6f, and FIG. A known "left and right end compression mode" is known (NHK Giken Monthly Report, September 1985, page 360, JP-A-62-84685, H04N 7/00). In the "left and right end compression mode" in FIG. 6g, black and black vertical lines (l ₁ ) and (l ₂ ) are multiplexed at the boundary between the normal part and the compressed part to reduce the unnatural feeling of the screen. But I try to reduce it.

In the future, if MUSE broadcasting is performed on multiple channels in the future, the mode setting will be stored for each channel, and the automatically stored mode will be read out when the channel is selected and set automatically. It is necessary to.

The converter is based on the aforementioned "UC-2" and the magazine "Electronic Technology, Vol. 31, No. 5, Vol. 408, published by Nikkan Kogyo Shimbun."
Izumi and Yanase's "MUSE / NTSC Converter" etc.
The outline of the circuit in the “zoom-up mode” will be described with reference to FIGS. 7 to 9.

FIG. 7 shows a satellite broadcast receiving system, where (40) is a BS antenna. (41) is the antenna body. (42) is a frequency conversion circuit that converts a received signal in the 12 GHz band into a 1 GHz band.

(43) is a BS tuner with a converter (44).
(45) is the signal of the desired channel out of the 1GHz band signal.
This is a frequency conversion circuit for converting into a 402, 78 MHz second intermediate frequency signal (2nd IF). (46) is an FM demodulation circuit.
(47) is an amplifier. (48) is a control circuit including a microcomputer for channel selection. The control circuit (48) is a PLL control circuit (5
0) to receive a signal of a desired channel.

(50) is an output processing circuit for normal broadcasting (for NTSC broadcasting), which performs triangular wave removal and the like. (51) is a synchronization separation circuit, which separates and outputs a synchronization signal.

Reference numeral (44) denotes a converter, which discriminates reception of a MUSE signal when a MUSE signal is input and outputs a determination signal from a terminal (44b). At this time, a keyed AFC pulse (P) indicating a clamp level period of the MUSE signal is also output. Output from terminal (44c). The converter (44) outputs the pseudo NTSC video signal from the terminal (44d).

 (52) is an operation switch unit.

(SW1) is an output switch, and (SW2) is an input switch.

(55) is a normal television receiver. (56) is
The MUSE decoder (57) is a high-definition television receiver. (58) is a MUSE disk player.

The keyed AFC pulse (P) from the MUSE decoder (56) and the converter (44) and the vertical synchronization signal from the synchronization separation circuit (51) are signals for receiving a desired channel without being affected by triangular waves in satellite broadcasting. And is well known (for example, JP-A-57-135582).

FIG. 8 shows the MUSE signals of 1125 horizontal scanning lines
The inside of the converter (44) for converting into five NTSC signals is schematically shown. (59) on the left side of the figure is the MUSE signal processing system.
Basically, various timing controls are performed by the synchronization signal and the clock signal from the clock synchronization reproduction circuit (91). Reference numeral (60) denotes an NTSC signal processing system. Basically, various timing controls are performed by a synchronization signal and a clock signal from a clock synchronization generation circuit (93).

In FIG. 8, (61) is an 8.1 MHz low-pass filter. (62) is a clamp circuit that performs a clamp operation during the horizontal synchronization period. (63) is an A / D conversion circuit that operates with a 16.2 MHz sampling clock.

(64) is a time axis expansion circuit, which is used to scan the MUSE signal scanning line 11
Out of 25, 1050 video signals in the center are expanded in time axis for NTSC signals. (65) is a 1H delay circuit for the MUSE signal. (66) and (67) are memories for expanding the time axis of the Y signal. The memory (66) is for even-numbered lines, and the memory (67) is for odd-numbered lines.

(68) is a vertical filter circuit for a luminance signal. (6
9) is a 1H delay circuit, and (70) is a vertical filter operation circuit.

(71) is a vertical filter circuit for the RY signal.
(72) is a shift register for the time axis expansion circuit, and (73) is
A shift register for the 1H delay circuit, and (74) is a vertical filter operation circuit.

(75) is a vertical filter circuit for the BY signal.
(76) is a time base expansion circuit, (77) and (78) are 1H delay circuits,
(79) is a vertical filter operation circuit.

(80) is a D / A converter for Y signal, (81) is a D / A converter for RY signal, and (82) is a D / A converter for BY signal. (83) is a low-pass filter for Y signal, (84) and (85)
Is a low-pass filter for RY and BY color difference signals, (8
6) is a matrix circuit.

(87) is an NTSC color encoder. (88) is a color modulation circuit, (89) is a color subcarrier oscillation circuit, 3579545 Hz
Oscillates at (90) is an addition circuit.

(91) is a clock synchronous reproduction circuit, which reproduces a 16.2 MHz clock signal, a frame pulse, and a horizontal synchronous signal synchronized with the clock component of the input MUSE signal. The clock synchronous reproduction circuit (91) determines whether the MUSE
It determines whether or not a signal is being input and outputs a determination signal. or,
Keyed AFC pulse corresponding to clamp level period (P)
Is also output.

Reference numeral (92) denotes a control timing signal generation circuit for generating various signals for controlling the circuits (65), (66), and (67) based on a signal from the clock synchronous reproduction circuit (91).

Reference numeral (93) denotes a clock synchronization generating circuit for generating horizontal synchronization and clock signals for NTSC. 10.0 of this circuit (93)
The 8 MHz reference signal is PLL controlled so as to synchronize with the 16.2 MHz clock signal for MUSE. (94) is a 1/45 divider circuit, (95) is a 1/28 divider circuit, (96) is a phase comparator, (9
7) is a low-pass filter, and (98) is a 10.08 MHz reference oscillation circuit. (99) is a 1/640 frequency dividing circuit for producing a horizontal synchronizing signal. The 1/640 frequency dividing circuit (99) is reset by the frame synchronizing signal of the 30 Hz MUSE signal from the clock synchronizing reproduction circuit (91).

(100) is a circuit (66) (67) (69) (72) (73) (76) (77) using a frame synchronization signal, a horizontal synchronization signal, and a 10.08 MHz clock signal from the clock synchronization generation circuit (93).
This is a control timing signal creation circuit for creating various signals for controlling (78). This circuit (100) also generates a vertical synchronizing signal from the horizontal synchronizing signal and the frame signal, and outputs a composite synchronizing signal (SYNC).

 The processing of the video signal will be briefly described.

The input MUSE signal is input to a time axis expansion circuit (64) via a low-pass filter (61), a clamp circuit (62), and an A / D conversion circuit (63). The MUSE signal (FIG. 9a) input to the time base expansion circuit (64) is delayed by 1H in the 1H delay circuit (65). This output is shown in FIG. 9c.

The writing to the memory (67) is controlled by the control timing signal generation circuit (92) described above, and the Y of the even line is controlled.
Only the central part of the signal and the color signal of the odd-numbered line (RY signal) is written (see FIG. 9c). The memory (67) is controlled as a FIFO memory, and reading is controlled by the control timing signal generation circuit (100) described above to output the signal of FIG. 9D. Of this signal,
Although the time axis expansion of the color signal is insufficient, the Y signal is time axis expanded to the normal value of the NTSC signal.

Also, the memory (66) is controlled in the same manner to perform time axis expansion as shown in FIG. 9Ab.

Then, the two Y signals in FIG. 9bd are input to a Y signal vertical filter circuit (68), subjected to vertical filtering, and output as Y signals.

The RY signal and BY signal of FIG.
After being input to the signal vertical filter circuit (71) and the BY signal vertical filter circuit (75) and expanded on the time axis, respectively,
A vertical filtering process is performed, and the RY signal, BY
Output as a signal.

These Y, RY, and BY signals are converted by a D / A conversion circuit (8
0) (81) (82), low-pass filter circuits (83) (84)
The signal is input to the color encoder circuit (87) via (85) and is converted into a color television video signal (NTSC signal).

The oscillation circuit (89) of the color encoder (87) does not perform PLL control contrary to common sense. The reason will be described.

As is well known, a normal NTSC signal satisfies the following conditional expression.

f _sc is the number of color subcarriers.

f _h is the horizontal synchronization frequency.

However, this is the case of color broadcasting with a field frequency of about 59.94 Hz and a horizontal synchronization frequency of 15.734266 KHz.

As described above, the field frequency of the MUSE signal is 60 Hz. The video signal of the converter created by converting the MUSE signal is also 60 Hz. Therefore, the horizontal frequency is also 15.75 KHz, which is the same as the black and white broadcasting standard. That is, the output video signal of the converter (44) that has converted the MUSE signal is the same as the black and white broadcast standard, and the ratio of the value to the color broadcast standard is also 1000 to 1001.

 Therefore, the above equation (1) does not hold.

Therefore, the oscillating circuit (87) of the chrominance subcarrier of the encoder (87) self-oscillates without synchronizing with the horizontal frequency and outputs a signal of about 3.579545 MHz. If the frequency of the color sub-carrier oscillation circuit (89) is forcibly controlled so as to satisfy the above equation (1), the frequency of the color sub-carrier changes by 0.1% from the normal value, and the frequency of the ordinary television receiver is reduced. The color synchronization circuit does not work properly.

The oscillation frequency of the color subcarrier oscillation circuit (89) and the MU
The relationship of the horizontal frequency (fh) of the video signal created from the SE signal is as follows.

In other words, the chrominance carriers are shifted by 3/11 cycles every horizontal period as shown in FIG.

Therefore, when the output of the converter is viewed on a black-and-white television, the color subcarrier has a dot pattern as shown in FIG.
Since it is almost inverted every horizontal scanning), it is canceled out by the spatio-temporal integration effect of the eyes, and is less noticeable.

Note that the frequency of this color subcarrier is described in
As shown in 7293 (H04N 11/20), the same frequency as before, Has been proposed.

However, the oscillation circuit (89) of the chrominance subcarrier of the NTSC encoder in FIG. For example, as shown in FIG. 12, if the phase of the color subcarrier shifts by 1.5 / 11 periods after one field (263H), an oblique pattern is generated due to dot interference.

(C) Problems to be solved by the invention In order to prevent this, an oscillating circuit (8
In 9), a high-precision and high-stability one that does not cause frequency deviation may be used.

However, such an oscillating circuit is expensive and cannot be adopted for consumer equipment.

An object of the present invention is to obtain a stable oscillation circuit.

Another object of the present invention is to provide a MUSE / NTSC converter suitable for reproducing a good color screen on a conventional TV.

(D) Means for Solving the Problems The present invention relates to a method for generating a chrominance subcarrier signal of a MUSE / NTSC converter (44), wherein the phase of the chrominance subcarrier signal of the pseudo NTSC signal is set between the fields of the pseudo NTSC signal. And the frequency of this color subcarrier signal is
An oscillation circuit (20) (20a) (20a ') for generating a color subcarrier signal of the pseudo NTSC signal is added to the MUSE signal so that the variation value is within ± 0.02% of the frequency of the color subcarrier signal of the signal. It is controlled by a PLL circuit (10) using a synchronized signal.

Further, according to the present invention, one input signal of the PLL circuit is a pseudo N
The horizontal synchronization signal of the TSC signal or a signal four times as large as the horizontal synchronization signal is used.

The present invention is also characterized in that the oscillating circuit (20a ') for generating the chrominance subcarrier signal of the pseudo NTSC signal is divided by 1/4 into the chrominance subcarrier signal.

The present invention also provides a MUSE / NTSC converter (44), wherein a frequency of the pseudo NTSC signal horizontal synchronizing signal generated in synchronization with a reference signal of the MUSE signal is compared with a frequency of the pseudo NTSC signal color subcarrier. PLL means (14 ') for controlling the oscillation circuit (20a') for generating the color subcarrier signal of the pseudo NTSC signal so as to synchronize the signal frequency with the ratio of 2500/11 with the reference signal of the MUSE signal. , 22 ', 16, 18).

(E) Function In the present invention, the quasi-NTSC signal color subcarrier signal is synchronized with the reference signal of the MUSE signal by the PLL circuit (10). The horizontal synchronizing signal of the pseudo NTSC signal is also synchronized with the reference signal of the MUSE signal. Therefore, this pseudo NTSC
The signal color subcarrier signal and the pseudo NTSC signal horizontal synchronizing signal are also synchronized, so that color disturbance can be stably and easily prevented.

Further, the frequency of the pseudo NTSC signal color subcarrier signal is set to 25 with respect to the frequency of the pseudo NTSC signal horizontal synchronization signal.
The ratio of 00/11 is such that the phase of the color signal in the 1H delay line is exactly inverted.

(F) Embodiment An embodiment of the present invention will be described with reference to FIG.

(10) is a PLL oscillation circuit for the color subcarrier signal function,
The circuit configuration itself is well known. (12) is 1
Input terminal for pseudo NTSC horizontal sync signal converted from 5.75KHz MUSE signal. (14) is a 1 / m frequency dividing circuit. (1
6) is a phase comparison circuit. (18) is a low-pass filter. (20) is a voltage-controlled oscillation circuit for producing a color subcarrier. (22) is a 1 / n frequency dividing circuit.

The feature of this circuit is that m and n of the frequency dividing circuits (14) and (22) are set to correspond to a non-standard 60 Hz video signal. With this setting, the oscillation circuit (10) operates without any inconvenience even if a video signal of a nonstandard (field frequency of 60 Hz) is input.

 The selection of m and n will be described.

First, the frequency f _sc ′ of this chrominance subcarrier signal must be within the synchronization range of the chrominance subcarrier signal of the television receiver. That is, this frequency f _sc ′ is a fluctuation value within ± 0.02% of the normal frequency f _sc .

(1-0.0002) · f _sc ≦ f _sc ′ ≦ (1 + 0.0002) · f _sc ……
(3) In order to prevent dot disturbance between fields, about 3/11 cycle in one horizontal scanning period (about 3/11 cycle because the present invention is slightly shifted from 3/11 cycle). It is sufficient that there is a phase shift of about 7/11 period between the fields. Assuming that dot disturbance can be prevented within a range of ± 20% of the 7/11 period, the following is achieved.

T _263H is the time required for 263 horizontal scanning. [F _sc ′ · T _263H ] is an integer part of a decimal point or more of f _sc ′ · T _263H .

Further, since the chrominance subcarrier signal is controlled by the PLL, it becomes as follows.

When the above equation is inserted into (3), (4a) and (4b), the following is obtained.

227.227 ≦ n / m ≦ 227.318 (6) 0.509 ≦ 263 × n / m− [263 × n / m] ≦ 0.764 (7) n and m are natural numbers, and [263 × n / m] is (263) × n / m).

M and n satisfying the above equations (6) and (7) are, for example, m = 4, n = 909, and at this time, n / m = 227.25, 263 × n / m− [263 × n / m]
= 0.75.

Another example is m = 11, m = 2500, where n / m = 227.273, 263 × n / m− [263 × n /
m] = 0.727.

The dot pattern is as shown in FIG. 2 when m = 4 and n = 909. When m = 11 and n = 2500, the result is as shown in FIG.

By the way, the pseudo NTSC from this MUSE / NTSC converter
Some TVs to which signals are input include a well-known comb filter. In general, many TVs currently use a glass delay line as an element for delaying a video signal by one horizontal scanning period (1H period). Then, the TV uses this glass delay line to delay the NTSC signal by 1H. The luminance signal component has the same phase as the original signal, and the chrominance signal component has the opposite phase. Then, the luminance signal is obtained by taking the sum of the non-delayed NTSC signal and the delayed NTSC signal, and the chrominance signal is taken out by taking the difference.

 The delay period of the 1H glass delay line is 1 / 15.734266KHz = 63.55555448 μsec.

When the pseudo NTSC signal of m = 4 and n = 909 is input to the TV, the chrominance subcarrier is as follows.

The delay period of the color subcarrier in the 1H glass delay line is Becomes That is, the color signal output from the 1H glass delay line is not out of phase, the comb filter does not operate normally, and the image quality is degraded by the comb filter.

When the pseudo NTSC signal of m = 11 and n = 2500 is input to the TV, the chrominance subcarrier is represented by the following equation.

In the 1H glass delay line, the delay period of the color subcarrier is Becomes In other words, the color signal output from the 1H glass delay line has a substantially opposite phase, and the image quality deterioration due to the comb filter can be reduced.

As described above, in this embodiment, the oscillation circuit (20) can be controlled in phase by the horizontal synchronizing signal to prevent dot interference between fields.

The circuit configuration of the oscillation circuit (20) is, as shown in FIG. 3, an oscillation circuit (20a) that oscillates at an integral multiple (l times) of f _sc ′.
And a 1 / l frequency dividing circuit (20b) that divides the frequency by 1.

Further, in a configuration in which the horizontal synchronizing signal and the color subcarrier signal are directly frequency-divided, the values of m and n cannot actually be set so large that the phase control is performed quickly. For this reason,
As shown in FIG. 4, the output of the oscillation circuit may be compared with a frequency four times the horizontal synchronizing signal component. In FIG. 4, (99a) is a 1/160 frequency dividing circuit, (99b) is a 1/4 frequency dividing circuit, (14 ') is a 1/11 frequency dividing circuit, and (22') is 1/1 frequency dividing circuit. A 2500 frequency dividing circuit, (20a ') is a voltage controlled oscillation circuit oscillating at about 14.32 MHz, and (20b') is a 1/4 frequency dividing circuit.

In the above color encoder, Y, BY, RY
Although a signal is input, an RGB signal may be input if an inverse matrix circuit is provided.

In this embodiment, the phase is controlled in order to eliminate the dot disturbance between the fields. However, the phase may be reduced by inverting the phase of the color subcarrier between the frames.

In the case where the pseudo NTSC signal of this embodiment is subjected to RF conversion, the audio carrier frequency may be in a relationship between the color subcarrier frequency and the frequency interleaving.

(G) Effects of the Invention As described above, according to the present invention, a stable high-quality chrominance subcarrier for a pseudo-NTSC signal with little dot interference can be created.

In particular, this MUSE / N
Even if a pseudo NTSC signal is output from the TSC converter (44), it is possible to reduce the image quality deterioration that occurs in the comb filter.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention. FIG. 2 is a diagram for explaining the operation. FIG. 3 is a diagram showing another example of the present invention. FIG. 4 is a view showing still another example of the present invention. FIG. 5 shows the MUSE signal, FIG. 6, FIG. 7, FIG.
FIG. 9 is a diagram for explaining a MUSE / NTSC converter, and FIG.
FIG. 0, FIG. 11, and FIG. 12 are diagrams for explaining a dot pattern by a color subcarrier signal. (44) MUSE / NTSC converter, (20) Oscillator circuit of about 3.58 MHz, (20a) Oscillator circuit oscillating at an integer multiple of about 3.58 MHz, (20a ') Oscillator circuit of about 14.32 MHz, (10 Oscillator circuit for color subcarrier (PLL means), (14) 1 / m frequency dividing circuit (first frequency dividing means), (14 ') ... 1/11 frequency dividing circuit (first frequency dividing means) , (22) ... 1 / n frequency dividing circuit (second frequency dividing means), (2
2 ') 1/2500 frequency dividing circuit (second frequency dividing means), (16) phase comparing circuit (phase comparing means), (18) low-pass filter.

Claims (1)

(57) [Claims] 1. 1125 horizontal scanning lines, 60 Hz field frequency
525 horizontal scanning lines, field frequency 60H
MUSE / NTSC converter to convert to z pseudo NTSC signal (44)
In the PLL means (10) (14 ', 14), the oscillation circuit (20a') for generating the color subcarrier signal of the pseudo NTSC signal is phase-synchronized with the horizontal synchronization signal at a ratio of 2500/11 to perform oscillation control. Two
2 ', 16,18) MUSE / NTSC converter.