On Fri, 25 Feb 2005 20:23:52 -0800, george_barr wrote:
[top-post re-arranged]
The Analog AD9858 DDS chip has a max of 2,000MSPS speed when using a
divide by 2 thing. So, does this mean that the maximum sine wave
frequency is 2,000M / 2 = 1GHZ Sine Wave?
No. The input clock can be up to 2 GHz, but when it is, it is mandatory to
use the divide by 2 feature, which slows the internal clock back down to 1
GHz. I have used that chip, but I am not re-reading the datasheet right
now. So if you think I am wrong, please quote me chapter and verse from
the datasheet.
And the 9858 is the fastest DDS that I know of. I don't think it is much
good beyond 400 MHz output.
I am looking for a DDS that can output upto a 1GHZ Sine Wave. Does
anyone know of a chip that can do this?
You should explore the possibility of using frequency multipliers
and/or mixers to attain your goals. For example, if you clock the DDS at 1
GHz, you can mix the 1 GHz with the DDS output to obtain either 1 GHz -
Fdds, or 1 GHz + Fdds, depending on how you filter the output. Fdds is the
DDS output frequency.
The DDS chip actually has a mixer built into it, but I think it is set up
for down-conversion only. So you probably want to find a mixer elsewhere.
Realistically, if you want to operate somewhere near 930 MHz, you should
probably operate the DDS at, say, 700 MHZ, then output 230 MHz, and
upconvert by mixing the 700 MHz with the DDS output to obtain 930 MHz
and 470 MHz. A high-pass filter should get rid of the 470 MHz. Note,
however, that I am not really an RF guy, so...
Also, please don't top-post. It forces others to read the thread
out-of-order.
--Mac