LF Stability

Terry Fox tfox@erols.com
Mon, 08 Feb 1999 19:30:42 -0500

No, it does not have quad outputs.  However, I am planning to run the DDS output at 4X the
necessary LO frequency, and use an external walking ring counter (2 flip-flops) to generate
a 90 degree delayed signal.  I run the AD818 output through a 74HCT14 to change the sine
wave to a square wave.  If the square wave has a 50% duty cycle, you can actually create a
90 deg. phase delayed signal by using both sides of a bit transition through 2 flip flops,
and then you can use a X2 oscillator frequency.

My LF receiver uses a 2.4576MHz IF, so a X4 LO at 9.83MHz just barely works with the
AD9832.  The 9850/9851 runs with a 125 or 180MHz clock, so they can be used thru 30MHz
easily, at a higher cost.

I think there are DDS devices from Harris and others that generate quad outputs and other
fun things, but they often use multiple ICs to create the full DDS, and tend to be more
costly and less available than the Analog Device parts.  Overall, the AD9832 looked like the
most fun for my applications.

I have created a prototype board layout, and Sandy is cleaning up the layout.  I have a
hard-wired prototype running now, but those pins and wires are too small!.  More on the
board and further design later.


Alberto di Bene wrote:

> Terry Fox wrote:
> > ...... snip
> > 6. I love the AD9832 DDS, and it's big brother the AD9850/51, and plan
> > to use them for lots of fun stuff.  It takes a 25MHz oscillator in, and
> > ...... snip
> Terry, does it have quadrature outputs ? They would be handy for an Hilbert-type
> direct-conversion receiver.
> If not, do you know of a DDS which does ? And, are you intending to produce a Postscript
> file for the PCB you are reading for the DDS ? Thanks,
> 73
> Alberto di Bene,  I2PHD