On 2/10/06, Sean H Breheny <shb7@netzero.net> wrote:
>
> Hi Sean S.,
>
> BTW, I like your name ;-)


Haha, yours isn't that bad either ;-)


I still don't have clear what your clock rate is and what your max output
> frequency is? You may not really be able to use a Sallen-Key type filter (at
> least if it involves an op-amp) because they usually have very limited
> bandwidth. The fastest commmonly available op-amps have a gain-bandwidth
> product of about 2GHz, meaning that they have a gain of 1 at 2GHz, so they
> are usable up to say 500MHz or so. These are expensive current-feedback
> types. BUT, most op-amps have a gain-bandwidth product of only about 1MHz,
> meaning that you can really only use them up to 100kHz at best.



100Khz is more than enough.  The DDS is actually  probably kind of overkill
as I don't need anything more than audio-frequency filtering up to no more
than about 25Khz, which should not be too much of a problem. I think that I
will select 10Mhz as the clock rate for my AD9834, and filter-simulations
that I have run, make it look like a 500Khz cutoff is just about right for
what I need.

In your first reply you stated that a phase shift does NOT change the shape
of a sine wave. I thought that some one told me that that was the case, but
the more I think of it, the less logical it sounds. The strange thing is
that I encountered some deformities during some spice simulations I run, but
I guess that I have to take a better look at it all, and check and see if
all is what it seems.

After I get all this sorted, I need to finish my PCB-Design and turn what is
on paper into a ready prototype on which I can start experimenting with
software... I can't wait!

Sean S
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist