JP4762440B2 - Video DAC device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an IC video DAC device (digital / analog converter device) used for a digital TV, DVD, game machine, etc., and more particularly to a multi-channel video DAC device.
[0002]
[Prior art]
A conventional color TV signal is formed as a composite color video signal (composite signal) N in which a luminance signal Y, a chroma signal C, a synchronization signal, and the like are combined, and is combined with the combined luminance signal Y in the receiver. The chromaticity signal (chroma signal) C is separated. It has been difficult to accurately perform Y / C separation between the luminance signal Y and the chroma signal C, which has been a cause of image quality degradation.
[0003]
In order to cope with this, in a video DAC device such as a digital TV that requires high image quality, in addition to the conventional composite signal N, a luminance signal Y and a chroma signal C, as in a so-called S video signal of a high resolution VTR, Are prepared separately to form a three-channel configuration. As a result, the TV viewer can use the desired output.
[0004]
[Problems to be solved by the invention]
Since the chroma signal C is a subcarrier (3.58 MHz in the NTSC system, 4.43 MHz in the PAL system), the first color difference signal BY and the second color difference signal RY are quadrature-phase modulated. Energy is distributed in the vicinity. This three-channel video DAC device may be integrated into an IC, and a parasitic capacitance Cp is formed between the signal wirings of each channel, so that the chroma signal C and the luminance signal Y are separated. It is inevitable that crosstalk of the chroma signal C occurs in the luminance signal Y. Further, since the chroma signal is similarly included in the composite signal N of the other channel, the luminance signal Y is also subjected to crosstalk by the chroma signal in the composite signal N.
[0005]
Thus, since the channel of the luminance signal Y is superimposed and influenced by the high frequency component of the chroma signal C from the other two channels in parallel, the crosstalk in the analog output of the luminance signal is further deteriorated and the image quality is lowered. There was a problem of inviting.
[0006]
Therefore, the present invention reduces crosstalk from other channels to a luminance signal channel in a video DAC device having a composite color video signal channel, a luminance signal channel, and a chromaticity signal channel, and prevents deterioration in image quality. With the goal.
[0007]
[Means for Solving the Problems]
The video DAC device of the present invention is a video DAC device having a composite color video signal channel, a luminance signal channel, and a chromaticity signal channel, which receives a digital video signal, converts the digital video signal into an analog video signal by the video DAC, and outputs the analog video signal. The chromaticity signal channel is provided with phase inversion means.
[0008]
The phase inversion means may be constituted by a digital inversion circuit provided on the video DAC input side of the chromaticity signal channel.
[0009]
In addition, it is desirable to provide delay means having a delay time corresponding to the processing delay time in the phase inversion means in the channel of the luminance signal Y constituting the color signal group together with the chromaticity signal C so that the timing of the signals is matched.
[0010]
Further, it is desirable to provide delay means having a delay time corresponding to the processing delay time in the phase inversion means in the composite color video signal channel so as to completely cancel the influence of crosstalk on the channel of the luminance signal Y.
[0011]
Thereby, in the video DAC device having the composite color video signal channel, the luminance signal channel, and the chromaticity signal channel, by canceling the crosstalk component from the chromaticity signal channel and the crosstalk component from the composite color video signal channel, It is possible to reduce crosstalk to the luminance signal channel and prevent deterioration of image quality.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the video DAC device of the present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a diagram showing a schematic configuration of a DAC portion of a video DAC device 10 according to the present invention, which is formed as a semiconductor integrated circuit device. In FIG. 1, Nd is an n-bit digital composite signal such as the NTSC system or the PAL system, and a luminance signal Y required for color video or a subcarrier (3.58 MHz for the NTSC system and 4.8 for the PAL system). 43 MHz) is a digital color TV signal that includes all of the chroma signal, the horizontal / vertical synchronization signal, etc. that are obtained by quadrature phase modulation of the first color difference signal BY and the second color difference signal RY. Note that n bits are, for example, 10 bits, and other digital signals are formed with the same number of bits unless otherwise specified. Yd is a digital luminance signal, which includes a horizontal synchronizing signal, a vertical synchronizing signal, and the like here. Cd is a digital chroma signal obtained by quadrature-modulating the first color difference signal BY and the second color difference signal RY with a subcarrier, and includes a subcarrier burst signal.
[0014]
Among the three-channel signals Nd, Yd, and Cd, the digital luminance signal Yd and the digital chroma signal Cd constitute one color signal group, and the digital luminance signal Yd and the digital chroma signal Cd are formed separately. Therefore, it is not necessary to perform Y / C separation on the monitor side, and an accurate color image can be obtained. The digital composite signal Nd alone constitutes a color signal.
[0015]
These three-channel signals, that is, the digital composite signal Nd, the digital luminance signal Yd, and the digital chroma signal Cd are formed from a set of color signals R, G, and B, and are supplied as signals in which the timing of each signal is adjusted to be the same. Is done.
[0016]
In the composite signal channel, the digital composite signal Nd is latched by the first latch circuit 11, delayed by the first delay circuit 12 having the delay time τ1, and n-bit data is decoded by the first decoder 13, and the first video. The analog signal is converted by the DAC 14 and output from the video DAC device 10 as an analog composite signal Na. Note that the decoder 13 decodes n-bit digital data into a predetermined m-bit code adapted to the first video DAC 14, and may not be provided depending on the configuration of the first video DAC 14. This also applies to other channels.
[0017]
In the luminance signal channel, the digital luminance signal Yd is latched by the second latch circuit 21, delayed by the second delay circuit 22 having the delay time τ 1, n-bit data is decoded by the second decoder 23, and is output by the second video DAC 24. It is converted into an analog signal and output from the video DAC device 10 as an analog luminance signal Na.
[0018]
Similarly, in the chroma signal channel, the digital chroma signal Cd is latched by the third latch circuit 31, the signal phase is inverted by the digital inversion circuit 32, n-bit data is decoded by the third decoder 33, and the third video DAC 34 is obtained. Is converted to an analog signal and output from the video DAC device 10 as an analog chroma signal Na.
[0019]
Here, the inverting circuit 32 inverts the phase of all signals including the period of the subcarrier burst signal included in the digital chroma signal Cd by the inverter circuit. When the time required for this inversion processing is τ1, the delay of the first delay circuit 12 and the second delay circuit 22 is the delay time τ1, and the timing of each channel is matched.
[0020]
CLK is a system clock supplied from the outside, and is supplied to each channel in common.
[0021]
Cp is a parasitic capacitance generated inside the video DAC device 10 between the outputs of the first video DAC 14, the second video DAC 24, and the third video DAC 34, and Cp ′ is also external to the video DAC device 10. This is the parasitic capacitance that occurs.
[0022]
In FIG. 1, a color signal group composed of an analog luminance signal Ya and an analog chroma signal Ca and a color signal of an analog composite signal Na are supplied to a TV receiver and a monitor, respectively. Then, in the TV receiver or monitor, signal processing corresponding to the input color signal, for example, color signal demodulation processing, RGB matrix processing, etc. is performed to obtain an R signal, a G signal, and a B signal. Become.
[0023]
Next, the operation of the video DAC device of the present invention will be described with reference to the circuit diagram for explaining operation in FIG. 2 and the signal waveform diagram for explaining operation in FIG.
[0024]
FIG. 2 is a diagram for simplifying the description by omitting the decoders 13, 23, and 33 of FIG. 1. The output side of the first video DAC 14 of the composite signal channel, the output side of the second video DAC 24 of the luminance signal channel, and Between each output side of the third video DAC 34 of the chroma signal channel, there is a parasitic capacitance Cp generated inside the video DAC device 10 and a parasitic capacitance Cp ′ (not shown) generated outside. . Through these parasitic electrostatic capacitances Cp and Cp ′, the channels influence each other according to their respective signals.
[0025]
The influence of the externally generated parasitic capacitance Cp ′ is the same as that of the internally generated parasitic capacitance Cp. Therefore, the following description will be made only on the internally generated parasitic capacitance Cp.
[0026]
The load equivalent circuit 40 is an equivalent circuit such as a signal processing circuit viewed from the output terminals of the analog composite signal Na, the analog luminance signal Ya, and the analog chroma signal Ca, and is formed by a capacitor C1 and a resistor R1, respectively. The Resistor R1 is typically 75 ohms and capacitor C1 is large. Driving power is supplied from the power supply potential Vcc and the reference potential Vss. The power supply potential Vcc and the reference potential Vss have a parasitic resistance Rp and a parasitic inductance Lp in the IC configuration.
[0027]
In FIG. 3, the analog luminance signal Ya has a horizontal synchronizing signal in the negative direction with the black level as a reference, and has a luminance level corresponding to the screen in the positive direction, as shown in FIG. The upper limit of the luminance level is the white level indicated by a broken line, and the lower limit is the black level. This luminance level varies depending on the luminance of the screen, but here it is represented by a straight line having a predetermined inclination for convenience of explanation. The analog chroma signal Ca has a sub-carrier burst signal and a chroma level obtained by quadrature-modulating the first color difference signal BY and the second color difference signal RY with the subcarrier as shown in FIG. is doing.
[0028]
The analog composite signal Na has a horizontal sync signal in the negative direction with reference to the black level, a subcarrier burst signal, and a luminance level according to the screen in the positive direction with the black level as a reference, as shown in FIG. The chroma level superimposed on the luminance level is obtained by quadrature-modulating the first color difference signal BY and the second color difference signal RY with the subcarrier.
[0029]
Thus, the analog composite signal Na is obtained by adding the analog luminance signal Ya and the analog chroma signal Ca. However, since the phase of the digital chroma signal Cd is inverted by the inverting circuit 32, the phase of the analog chroma signal Ca is opposite to that of the chroma signal component (burst signal and chroma level) included in the analog composite signal Na. It is a phase. Although the phase of the analog chroma signal Ca is inverted, phase inversion is performed including a burst signal used as a reference for color reproduction, so there is no inconvenience when used in a monitor or the like.
[0030]
When the video DAC device 10 starts operating, in the composite signal channel, the digital composite signal Nd is delayed by a predetermined time τ1, converted by the first DAC 14, and output as an analog composite signal Na. Similarly, in the luminance signal channel, the digital luminance signal Nd is delayed by a predetermined time τ1, converted by the second DAC 24, and output as an analog luminance signal Ya. Further, in the chroma signal channel, the digital chroma signal Nd is phase-inverted by the inversion circuit 32, converted by the third DAC 34, and output as the analog chroma signal Ca.
[0031]
The analog composite signal Na, the analog luminance signal Ya, and the analog chroma signal Ca influence each other through the parasitic capacitance Cp according to the respective signals. In particular, since the analog composite signal Na and the analog chroma signal Ca include subcarrier frequency components (burst signal and chroma level), the analog luminance signal Ya includes this subcarrier frequency as indicated by a dashed line arrow in the figure. The effect of crosstalk due to components tends to increase.
[0032]
However, in the present invention, the analog chroma signal Ca and the analog chroma signal included in the analog composite signal Na are set so as to be in opposite phases, so that the analog chroma signal Ca with respect to the analog luminance signal Ya is used. The crosstalk and the crosstalk due to the analog chroma signal included in the analog composite signal Na cancel each other. Therefore, crosstalk to the luminance signal channel is reduced, and deterioration in image quality is prevented.
[0033]
In order to better cancel out the crosstalk, in the video DAC device 10, their arrangement is symmetrical with respect to the luminance signal channel so that the influence from the composite signal channel and the influence from the chroma signal channel on the luminance signal channel are equal. It is desirable to consider such as.
[0034]
Note that the analog luminance signal component and the luminance signal Ya included in the analog composite signal Na also contain frequency components, but there is no particular problem because the degree of influence by these frequency components is small.
[0035]
Further, when the luminance signal Y of three channels, the chroma signal C, and the composite signal N are used at the same time (for example, when using a CRT monitor and a video deck, or when using a plurality of monitors), The load is driven simultaneously. In this case, for the video DAC device that is made into an IC, an output current that is larger than the planned output current is supplied, and these output currents increase and decrease at the same time, so that the power supply voltage of the IC fluctuates. This may cause image quality degradation.
[0036]
In the present invention, since the analog chroma signal component included in the analog composite signal Na and the analog chroma signal Ca are in opposite phases, the three-channel luminance signal Y, the chroma signal C, and the composite signal N are simultaneously transmitted. Even when it is used, the current due to the analog chroma signal component and the current due to the analog chroma signal Ca do not overlap each other, and since they are in opposite phase, when one is the discharge current, the other is in the relationship of the sink current. Accordingly, fluctuations in the power supply voltage of the IC can be reduced.
[0037]
The operation in the case of the simultaneous drive will be described with reference to FIG. 2. A current i1 due to the analog chroma signal component included in the analog composite signal Na is supplied from the power supply potential Vcc via the first video DAC 14 to a predetermined value of the load equivalent circuit 40. Flows into the load. At the same time, the current i2 due to the analog chroma signal Na flows from the other predetermined load of the load equivalent circuit 40 to the reference potential Vss via the third video DAC 34.
[0038]
The fluctuation of the power supply potential Vcc (or the reference potential Vss) is not only the resistance voltage drop due to the parasitic resistance Rp but also the influence of the induced voltage drop due to the change of the current flowing through the parasitic inductance Lp. That is, since the voltage drop is expressed by Rp (i1 + i2) + Lp (di1 / dt + di2 / dt), it becomes particularly large when the current i1 and the current i2 change simultaneously in the same direction.
[0039]
However, in the present invention, as shown by the solid arrow line and the broken arrow line in FIG. 2, the increasing and decreasing directions of the currents i1 and i2 are reversed, so that the induced voltage drops cancel each other, and the resistance voltage drop is reduced by half. Therefore, the fluctuation of the power supply potential Vcc (or the reference potential Vss) is reduced.
[0040]
Thus, since the current i1 and the current i2 do not flow superimposed on the power supply potential Vcc (or reference potential Vss), fluctuations in the power supply potential Vcc (or reference potential Vss) in the case of simultaneous driving are reduced. . Accordingly, high image quality can be provided accordingly.
[0041]
In the above embodiment, the first delay circuit 12 and the second delay circuit 22 having the same delay time as the time τ1 required for the inversion processing in the inversion circuit 32 are provided in the composite signal channel and the luminance signal channel, respectively. I am going to do that. However, when the time τ1 required for the inversion process is short and the phase difference between the current i1 due to the analog chroma signal component included in the analog composite signal Na and the current i2 due to the analog chroma signal Ca is within a small range, the first The delay circuit 12 does not need to be provided and can be deleted.
[0042]
For the second delay circuit 22, since the analog chroma signal Ca and the analog luminance signal form one color signal, it is desirable to align the timing as much as possible, but the time τ1 required for the inversion process is short, and the time τ1 If the difference is acceptable as a color image, it can also be deleted.
[0043]
Further, depending on the driving capability of the first video DAC 14 to the third video DAC 34, a driver circuit may be provided on the output side of the first video DAC 14 to output from each driver circuit.
[0044]
【The invention's effect】
According to the video DAC device described in this specification, in the video DAC device having the composite color video signal channel, the luminance signal channel, and the chromaticity signal channel, the chromaticity signal channel is provided with the phase inversion means, By canceling the crosstalk component from the signal channel and the crosstalk component from the composite color video signal channel, the crosstalk to the luminance signal channel can be reduced and the deterioration of the image quality can be prevented.
[0045]
Further , according to the video DAC device described in the present specification , the phase inversion means is constituted by the digital inversion circuit provided on the input side of the video DAC of the chromaticity signal channel, so that the inversion process is easy. .
[0046]
Further , according to the video DAC device described in the present specification , the delay of the channel of the luminance signal Y constituting the color signal group together with the chromaticity signal C has a delay time corresponding to the processing delay time in the phase inversion means. Since the means is provided, the timing of the signal of each channel can be matched, and the image quality can be improved.
[0047]
Further , according to the video DAC device described in this specification , the composite color video signal channel is provided with delay means having a delay time corresponding to the processing delay time in the phase inversion means. It is possible to completely cancel the influence of crosstalk.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a video DAC device according to a first embodiment of the present invention.
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]
10 video DAC device 11 first latch circuit 12 first delay circuit 13 first decoder 14 first video DAC
21 Second latch circuit 22 Second delay circuit 23 Second decoder 24 Second video DAC
31 Third latch circuit 32 Inversion circuit 33 Third decoder 34 Third video DAC
Yd Digital luminance signal Nd Digital composite signal Cd Digital chroma signal Ya Analog luminance signal Na Analog composite signal Ca Analog chroma signal 40 Load equivalent circuit Vcc Power supply potential Vss Reference potential

Claims (5)

In a video DAC apparatus having a composite color video signal channel, a luminance signal channel, and a chromaticity signal channel, to which a digital video signal is inputted, converted into an analog video signal by a video DAC, and output.
Phase inverting means is provided in the chromaticity signal channel ,
A video DAC device comprising delay means having a delay time corresponding to a processing delay time in the phase inversion means in the luminance signal channel .   2. The video DAC device according to claim 1, wherein a delay unit having a delay time corresponding to a processing delay time in the phase inversion unit is provided in the composite color video signal channel.   In a video DAC apparatus having a composite color video signal channel, a luminance signal channel, and a chromaticity signal channel, to which a digital video signal is inputted, converted into an analog video signal by a video DAC, and output.
  Phase inverting means is provided in the chromaticity signal channel,
  A video DAC device comprising delay means having a delay time corresponding to a processing delay time in the phase inversion means in the composite color video signal channel.   4. The video DAC device according to claim 1, wherein the phase inversion means is constituted by a digital inversion circuit.   By supplying the output of the video DAC in each channel to the output destination of the analog video signal without phase inversion other than the phase inversion by the phase inversion means, the composite color video signal and the chromaticity signal are in opposite phases to each other. The video DAC device according to claim 1, wherein the video DAC device is supplied to an output destination of the analog video signal.

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