Timothy Miller wrote:
On 3/16/06, James Richard Tyrer <[EMAIL PROTECTED]> wrote:
Getting back to the RAMDAC.
I can't find any that are not intended for TV use -- although I might
look some more if I have time.
So, if we want to implement this, I would suggest that we have the SRAM
in the FPGA. Therefore, the only circuit requirement would be that ALL
the DAC inputs be connected to the FPGA then the implementation could be
done however we want by just changing the FPGA programing.
I guess I forgot to mention this. The FPGA has gobs of RAM in it.
There will definitely be three LUTs for video. There's not a lot we
can do to get MORE than 8 bits out, although we can temporally
modulate it to trick the eye into seeing more shades.
The extra RAMDAC bits are used for gamma and color correction. You
still have only 8 bits per color in memory.
The Philips 3xDAC has 10 bits per channel, and we are grounding the 2
LSBs rather than connecting them to the FPGA.
Do consider using the less expensive DAC which is made for this specific
use and has RS-170 buffers already built in.
The 330MHz DAC isn't that bad, is it? We're not populating the highspeed ones.
Note that if we do go with the design, I should point out that the black
voltage for RS-170 is NOT 0 volts but rather 0.095 volts so a slight
bias is needed for the video out buffers. Perhaps this would be enough
so that they could be run with single supply if we used a different amp
that was designed for single supply.
Isn't there only an amp for the highspeed DAC? Still, it's important
that we get this right too.
Yes, I have now found the Philips TDA8777 which is about the same as the
Analog Devices one except for the sync and blanking.
--
JRT
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