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HDTV DAC to generate Composite video signal

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mami_hacky

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hdtv dac

Hi,
Any body can answer this question:

I have a ths8133 from Texas instruments which is an DAC for HDTV standard. it contains 3 independent 80MSPS DACs inside. I wanted to know if it is possible for me to use this chip for generating 3 independent normal tv (e.g. ntsc ) video composite signals.
suppose that i have an fpga before this chip and i make the data ready to exactly meet the needs of dacs.
thanks,
mami_hacky.
 

Vamsi Mocherla

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hd-dac tv

Dear mami_hacky,

Well, in one of the modes, you can tie M1 and M2 inputs to ground and then send the 4:4:4 signal into each of the DACs. So the each DAC is driven independently from that input port.
 

hcet

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how to generate a composite tv signal

Hi mami_hacky,
I don't think you can use a THS8133. The signal would be monocrome. Use an ADV7170 or similar **broken link removed**. I don't know any encoders from TI which you could use. If you insist in TI you can youse a DSP and you would not need a FPGA to do data formatting.
Regards, ep20k.
 

mami_hacky

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hd-tv-dack.ru

dear ep20k,
why you say that the signal gets monocrome. Yes , i know that great product from analog devices, but, if I do a correct data formatting , then, can i make a composite color video signal usings DACs in 8133?
thanks,
mami_hacky.
 

hcet

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generate a ntsc signal

Dear mami_hacky,
how do you want to get the croma in? I simply have no clue, how you wanna get the crominance signal into your ntsc-output-signal with the THS8133. Please explain it more detailed , i'm willing to learn.
Good luck with your project.
Regards, ep20k.

PS: Why don't you try to get hold on an FAE from TI to answer your question. They are usuallly helpfully, cause they also want to get input from 'stupid' guys like us to ask the right questions themself....
 

    mami_hacky

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mami_hacky

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ths8133

Dear ep20k,
OK! It seems that I have not understood the principles of video signals correctly, but let me ask another question:
What is a composite video signal, a basic definition says that it is a kind of video signal which has all of the color and timing information in just one signal.
if this is true then i have just one signal which contains croma and luminance inside, and one dac should be able to generate it.
what do you think? where is my mistake?
thanks,
mami_hacky.
 

Vamsi Mocherla

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dac circuit for dtv

Dear Friends,

Well, the signaling could be either GRB or YCrCb with the first one being only color channels. The second one is Y - Luminanance Cr - Chroma Difference for Red and Cb - Chroma Difference for blue. You cannot use a single DAC even when the encoding is 1X10bit 4:2:2(this will have a port driving with a single channel) . The output will be in three channels in the VDAC experience I have.
 

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making a composite video signal

Hi mami_hacky,

It seems that I have not understood the principles of video signals correctly, but let me ask another question:
What is a composite video signal, a basic definition says that it is a kind of video signal which has all of the color and timing information in just one signal.
if this is true then i have just one signal which contains croma and luminance inside, and one dac should be able to generate it.

Basically you are right, one DAC is enough. But! Why don't you just compare the functional block diagrams of ADV7170 and THS8133. DAC A of ADV7170 delivers the composite video signal. There are some blocks missing in the THS8133 to generate a composite video signal. If you want I'll give you the SMPTE standard for NTSC, which is pretty easy to understand.
Regards, ep20k.
 

mami_hacky

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generating color composite video signal in fpga

:( OK! really thanks for help,
dear ep20k, would you please upload the standard here, I think it will be useful for all of us.

Thanks,
mami_hacky.
 

hcet

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generate color composite ntsc

Hi mami_hacky,
the 170M is the original standard. EG 27 is supplemental information for ANSI/SMPTE
170M and background on the development of NTSC color standards.
Enjoy, ep20k.
 

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