----- Original Message -----
Sent: Friday, January 20, 2006 1:29
Subject: Re: [Xylo-SDR] FPGA pin names
Phil has been looking at that, maybe he can tell us what he thinking on
I think you need a DAC and a elliptical filter. you may
want to look at the DDS-60 board, it has all the components all figured out
for the filter and amplifier, except the DAC part
Phil Harman, or
anybody please chime in so Leon can put it in before making a
We have been discussing how to make a cleaner DDS, and
it requires a high precision Sine table with as many as 32K to 64K entries.
If we use the internal RAM to hold those values, it being very fast, we
might need RAM on the outside for use in buffers, etc. By the way, how wide
is the RAM that you have put in? A lot of the boards that have RAM have one
chip that is 16 bits wide, so every 10 ns you can pull out a 16 bit
precision number to feed the DAC or FX2. If the internal RAM is not big
enough then we are going to need to use the external RAM and it needs to be
16 bit wide to minimize the number of fetches.
This where a second
precision optional clock device besides the 24.4xx MHz comes in feeding a
clock input pin, you want the DDS STATE clock as high as the RAM will
tolerate, if we use internal RAM for the Sine table, our clock could be in
the 200MHz range, which would give better resolution and lower
We really need to get together on TeamSpeak to make
sure we are not leaving something critical out of the board.
Of course all of these components are optional and you
populate the board with them if needed only.