JP2002344988A - Video digital/analog converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video digital/analog converter formed to be an IC and having a plurality of video signal channels that can reduce fluctuations in a power supply voltage of the IC and prevent deterioration in the image quality without the need for an especially increased power supply capacity even when using a plurality of monitors at the same time. SOLUTION: The video digital/analog converter receiving a digital video signal, converting it into an analog video signal, outputting the analog video signal, and having a plurality of video signal channels is provided with a delay means with a prescribed delay time placed in a video signal channel of at least a color signal group including a luminance signal to provide a timing difference to an output current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a digital TV,
Video D made into IC used for DVD, game machine, etc.
Regarding AC devices (digital-to-analog converter devices)
In particular, it relates to a multi-channel video DAC device.

[0002]

2. Description of the Related Art A conventional color TV signal is formed as a composite color video signal (composite signal) in which a luminance signal Y, a chromaticity signal (chroma signal) C, a synchronizing signal, and the like are compounded. And the combined luminance signal Y and chroma signal C are separated. It is difficult to accurately perform the Y / C separation of the luminance signal Y and the chroma signal C, and this has caused a deterioration in image quality.

In order to cope with this, in a video DAC device such as a digital TV which requires high image quality, in addition to the conventional composite signal N, a color TV signal such as a so-called S video signal of a high-resolution VTR is used. A luminance signal Y and a chroma signal C are separately prepared, and a total of three channels is formed. Further, recently, the chroma signal C itself is a signal obtained by mixing two color signals of a red color difference signal RY (hereinafter, U) and a blue color difference signal BY (hereinafter, V). To get high accuracy,
The color TV signal has a three-channel configuration using a first color difference signal U and a second color difference signal V in addition to the luminance signal Y.

For this reason, in a video DAC device which is a part of a video signal processing device, a video DAC device comprising a luminance signal Y, a composite signal N, and a chroma signal C is used in order to cope with any usage. One channel of three channels, a luminance signal Y, a first color difference signal U, and a second color difference signal V
Is used to form a total of six channels, including three channels of the second stream using. This gives T
The V viewer can appropriately use the signal output desired to be used.

[0005]

In the video DAC device having the six-channel structure, any one of the color signal groups constituting the color TV signal is used as an output signal so that it can be driven without any particular problem. It is configured. However, the case where the luminance signal Y and the chroma signal C and the composite signal N of the three channels of the first stream are used simultaneously, or the case where the three channels of the first stream and the three channels of the second stream are used simultaneously ( For example, CRT
In the case where a monitor and a VCR are used or a case where a plurality of monitors are used), a plurality of loads are driven simultaneously. In this case, the integrated video DA
For the C device, an output current larger than the expected output current is supplied, and those output currents increase and decrease at the same time, so that the power supply voltage of the IC fluctuates and causes deterioration of image quality. .

In view of the above, the present invention provides a video DAC device having a multi-channel video DAC that is integrated into an IC, even if a plurality of monitors are used at the same time, without increasing the power capacity of the IC. An object of the present invention is to reduce voltage fluctuation and prevent image quality deterioration.

[0007]

Video D according to claim 1
An AC device receives a digital video signal, converts the digital video signal into an analog video signal by a video DAC, and outputs the analog video signal.
The apparatus is characterized in that delay means having a predetermined delay time is provided in a video signal channel of at least one color signal group.

According to the video DAC device of the present invention, a video signal channel of a color signal group including a luminance signal includes:
Since a delay means having a predetermined delay time is provided to make the output current supplied to the load have a time difference, power supply fluctuation, that is, voltage fluctuation is reduced. Therefore, even when a plurality of monitors and the like are used at the same time, deterioration of image quality is reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a video DAC device according to the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a portion relating to a DAC of a video DAC device 10 of the present invention, and is formed as a semiconductor integrated circuit device. In FIG. 1, Y
d1 is an n-bit first digital luminance signal, which includes components such as a horizontal synchronizing signal and a vertical synchronizing signal. The n bits are, for example, 10 bits, and other digital signals are formed with the same number of bits unless otherwise specified. Nd is NTSC system or PAL
The composite signal includes a luminance signal Y required for a color image and a subcarrier (3.58 MHz in the NTSC system).
In the PAL system, the first color difference signal B-
Y, a chroma signal obtained by orthogonally modulating the second color difference signal RY, a horizontal / vertical synchronization signal, and the like are all included.
Cd is a digital chroma signal, and the first color difference signal B
−Y, the second color difference signal RY.

Of the three channel signals, one color signal group is formed by the first digital luminance signal Yd1 and the digital chroma signal Cd, and the first digital luminance signal Yd1 and the digital chroma signal Cd are separately formed. Therefore, there is no need for Y / C separation, and a highly accurate color image can be obtained. The digital composite signal Nd alone forms a color signal group.

[0012] Yd2 is a second digital luminance signal, which is the same as the first digital luminance signal Yd1.
Ud is the digital first color difference signal BY, and Vd
Is a digital second color difference signal RY. These three channel signals, that is, the second digital luminance signal Yd2
, The digital first color difference signal Ud and the digital second color difference signal Vd constitute one color signal group. In this color signal group, since the luminance signal and each color difference signal are all separately constituted, not only the Y / C separation but also the separation of the chroma signal is not required, so that a more accurate color image can be obtained. it can.

The signals of these six channels, that is, the first
A digital luminance signal Yd1, a digital composite signal Nd, a digital chroma signal Cd, a second digital luminance signal Yd2, a digital first color difference signal Ud, and a digital second color difference signal Vd are formed from a set of color signals R, G, and B. , Are supplied as signals whose timings are adjusted in the same manner.

The signals of the six channels are the same as those of the first three channels.
1 (11-1 to 11-3), the digital data is latched and converted into analog signals by the first DAC 12 (12-1 to 12-3), and the analog signals are converted into the first driver 13 (13-1 to 13-1). 13-3), the first
Analog luminance signal Ya1, analog composite signal N
a, Output as analog chroma signal Ca.

Here, the digital composite signal Nd
Channel, the first latch circuit 11-2 and the first
A first signal having a predetermined delay time τ1 with the DAC 12-2
A delay circuit 14 is provided. As a result, a time difference corresponding to the delay time τ1 is formed between the first analog luminance signal Ya1 and the analog chroma signal Ca forming one color signal group and the analog composite signal Na forming the other color signal group.

For the signals of the second three channels, digital data is latched by a second latch circuit 21 (21-1 to 21-3), and the latched digital data has a predetermined delay time τ2. 2 delay circuit 24
After being respectively delayed by (24-1 to 24-3), the signals are converted into analog signals by the second DAC 22 (22-1 to 22-3), and the analog signals are converted to the second signals.
The signals are output as the second analog luminance signal Ya2, the first analog color difference signal Ua, and the second analog color difference signal Va via the driver 23 (23-1 to 23-3). The predetermined delay time τ2 is set to a length different from the delay time τ1.
If the delay times τ1 and τ2 are set to the same time, the number of simultaneous changes increases, but the delay circuit can be omitted.

As a result, the second analog luminance signal Ya
2. A color signal group composed of the analog first color difference signal Ua and the analog second color difference signal Va is converted into a color signal group composed of the first analog luminance signal Ya1 and the analog chroma signal Ca, and the analog composite signal Na. And the other color signals
2, and a time difference [tau] 2- [tau] 1 can be different color signal groups. The delay times τ1, τ2 and the time difference τ2−τ1 are preferably large in order to obtain the effect of the present invention, but are determined in consideration of an increase in the area of the IC required for the configuration of the delay circuit.

In FIG. 1, the first analog luminance signal Ya1
And a color signal group composed of an analog chroma signal Ca, a second analog luminance signal Ya2, and an analog first signal.
A color signal group composed of a color difference signal Ua, an analog second color difference signal Va, and an analog composite signal Na
Are supplied to the TV receiver and the monitor, respectively. Then, in the TV receiver or the monitor, signal processing according to the input color signal, for example, color signal demodulation processing, RGB matrix processing, or the like is performed to obtain an R signal, a G signal, and a B signal. Become.

CLK is a system clock supplied from the outside, and the first latch circuit 11, the first DAC
12, the first delay circuit 14, the second latch circuit 21, the second D
AC 22 is supplied to the second delay circuit 24.

Next, the operation of the video DAC device of the present invention will be described with reference to the circuit diagram for explaining the operation of FIG. 2 and the signal waveform diagram for explaining the operation of FIG. 2 and 3, the channels of the first digital luminance signal Yd1 and the second digital luminance signal Yd2 are taken as representatives from each color signal group.

In FIG. 2, the first load equivalent circuit 30 and the second load equivalent circuit 40 are provided with a first analog luminance signal Ya1.
And an equivalent circuit such as a load circuit viewed from the output terminal of the second analog luminance signal Ya2.
1 and a resistor R1. The resistor R1 is typically 75 ohms, the capacitor C1 is large and the video D
The driving power is supplied from the power supply potential Vcc and the reference potential Vss of the AC device 10. On the other hand, the power supply potential Vcc and the reference potential Vss have a parasitic resistance Rp and a parasitic inductance Lp in the IC configuration.

In FIG. 3, the first analog luminance signal Ya
Reference numeral 1 denotes a horizontal synchronization signal in the negative direction with reference to the black level and a luminance level corresponding to the screen in the positive direction, as shown in FIG. The upper limit of the luminance level is a white level indicated by a broken line, and the lower limit is a black level. FIG. 6B shows the second analog luminance signal Ya2 'when the second delay circuit 24 is not provided, and the first analog luminance signal Y2'.
The waveform and timing are exactly the same as a1. FIG. 3C shows a second analog luminance signal Ya2 according to the present invention, which has the same waveform as the first analog luminance signal Ya1, but its timing is shifted by the delay time τ2 of the second delay circuit 24. I have.

Now, when the first driver 13 is driven,
A current i1 flows from the power supply potential Vcc to the first load equivalent circuit 30 via the output terminal of the first analog luminance signal Ya1. Similarly, when the second driver 23 is driven, a current i2 flows from the power supply potential Vcc to the second load equivalent circuit 40 via the output terminal of the second analog luminance signal Ya2. When these currents i1 and i2 flow through the parasitic resistance Rp and the parasitic inductance Lp, a voltage drop occurs, and a voltage applied as a power supply voltage to the first driver 13, the second driver 23, and other drivers (not shown). However, it fluctuates. Similarly, when the currents i1 and i2 are absorbed by the reference potential Vss, the reference potential also changes.

As shown in FIGS. 3A and 3B, the first,
When the timings of the second luminance signals Ya1 and Ya2 'are exactly the same, not only the resistance voltage drop due to the parasitic resistance Rp but also the induced voltage drop accompanying the change in the current flowing through the parasitic inductance Lp is simultaneously received. The effect is large. That is, the voltage drop is Rp (i1 + i2) + Lp (di1 / dt + di2
/ Dt), it is particularly large when the current i1 and the current i2 change simultaneously.

However, as shown in FIG. 3 (c), in the present invention, the timing of the first analog luminance signal Ya1 and the timing of the second analog luminance signal Ya2 are shifted by the delay time τ2. The drop does not occur at the same time, and the voltage drop is reduced.

In particular, in the case of the analog luminance signal, the signal level changes drastically at the falling (a) and rising (b) points of the synchronizing signal, and at the starting point (c) and ending point (d) for each line. However, since this change is temporally dispersed between the first analog luminance signal Ya1 and the second analog luminance signal Ya2, the induced voltage drop due to the current change is reduced.

Further, since the superimposed luminance level is also reduced, it can be expected that the resistance voltage drop is also reduced.

As described above, fluctuations in power supply, that is, fluctuations in voltage can be reduced, so that deterioration in image quality can be reduced even when a plurality of monitors are used at the same time.

In the examples shown in FIGS. 2 and 3, as a representative example, the first analog luminance signal Ya1 is selected from the color signal group.
And the second analog luminance signal Ya2 have been described. Regarding other signals, that is, the analog chroma signal Ca, the analog first color difference signal Ua, the analog second color difference signal Va, and the analog composite signal Na, although the signal waveforms themselves are different, the current flows with the start of the video signal period. At the beginning, stopping at the same time as the end is the same, and their loads are the same as the load equivalent circuit 30 and the like according to the standard such as TV. Therefore, the first analog luminance signal Y is also obtained as a color signal group to which other signals are added.
The same operation and effect as those described for a1 and the second analog luminance signal Ya2 can be obtained.

The channels in which the first delay circuit 14 and the second delay circuit 24 are provided are not limited to the example of FIG. 1, but three color signal groups, that is, a first digital luminance signal Yd1 and a digital chroma signal Cd, or The digital composite signal Nd or the first digital luminance signal Yd1, the digital first color difference signal Ud, and the digital second color difference signal Vd can be provided in any two color signal groups.

The delay circuit is an analog delay circuit, and the first delay circuit 14 and the second delay circuit 24 are replaced by
It can be provided on the output side of the first DAC 12 and the second DAC 22, and in that case, a clock signal to each delay circuit becomes unnecessary.

Further, the first DAC 12 and the second DAC 22
When the driving capability of the first driver 13 can be secured,
The second driver 23 may be omitted, and each analog signal may be directly output.

The second digital luminance signal Yd2, the digital first color difference signal Ud, and the digital second color difference signal Vd
A set of color signals Rd, Gd, Bd may be used instead of one color signal group composed of d.

[0034]

According to the video DAC apparatus of the present invention, a delay means having a predetermined delay time is provided in the video signal channel of at least one color signal group, so that the output current supplied to the load has a time difference. Therefore, fluctuations in power supply, that is, fluctuations in voltage are reduced. Therefore, even when a plurality of monitors and the like are used at the same time, deterioration of image quality is reduced.

[Brief description of the drawings]

FIG. 1 is a video DAC according to a first embodiment of the present invention.
FIG.

FIG. 2 is a circuit configuration diagram for explaining the operation of the present invention.

FIG. 3 is a signal waveform diagram for explaining the operation of the present invention.

[Explanation of symbols]

 Reference Signs List 10 video DAC device 11 first latch circuit 12 first DAC 13 first driver 14 first delay circuit 21 second latch circuit 22 second DAC 23 second driver 24 second delay circuit Yd1 first digital luminance signal Nd digital composite signal Cd digital Chroma signal Yd2 Second digital luminance signal Ud Digital first color difference signal Vd Digital second color difference signal Ya1 First analog luminance signal Na Analog composite signal Ca Analog chroma signal Ya2 Second analog luminance signal Ua Analog first color difference signal Va Analog second Color difference signal 30 First load equivalent circuit 40 Second load equivalent circuit Vcc Power supply potential Vss Reference potential

Continued on front page F-term (reference) 5C021 PA42 PA86 SA21 5C066 AA03 CA05 KC11 KE20 5J022 AB01 BA01 CA10 CE04 CE08 CG01

Claims (1)

[Claims] A digital video signal having a plurality of video signal channels for receiving a digital video signal, converting the digital video signal into an analog video signal by a video DAC, and outputting the analog video signal.
The video DAC device according to claim C, wherein delay means having a predetermined delay time is provided in a video signal channel of at least one color signal group.