EMRFD Message Archive 1649

Message Date From Subject
1649 2008-05-23 07:29:23 Kevin Wheatley AD9912 DDS clock source – just a thought?
With the release of the AD9912 DDS there has been a surge of
interest for a good 1Ghz clock source.
Not fully understanding the issues, would the proposal below be
worth experimenting with?

Crystek have recently introduced a new VCO – CVCO55CX-1000-1000, the
performance specs look
pretty good to me. If this was phase lock looped to a 10Mhz GPS,
would this be sufficient
as a clock for the AD9912.


10Mhz --- Phase det --- Diff Amp --- VCO -- Buffer Amp --- 1Ghz out
1653 2008-05-23 09:28:43 Art Re: [emrfd] AD9912 DDS clock source – just a thought?
Hi Kevin,

Phase locked 10 MHz sources are not the best
source if a clean DDS output is needed. The 10
MHz output from any VCO is going to have
relatively high phase noise, and the
multiplication to 1 GHz is going to multiply the
phase noise as well as the original 10 MHz
signals frequency. Use the phase locked DDS if
you need accuracy of the frequency, but not for a
DDS clock if you need a clean output.

If you need a very clean 1 GHz source to clock a
DDS, you can buy a ready made partial kit from
I0CG. He makes a small PCB with a helical
resonator and a MMIC amplifier to produce an
output at 500 MHz (for the 9951 through 9954 DDS
chips). I do not know if he makes a similar product for the 9912 DDS.

I have Valpey Fisher oscillators for sale, which
are known to be clean and are much cheaper than
other high performance oscillators you can get.
Digikey has helical resonators in stock and I
have MMIC's for sale also. A small pcb to hold
the MMIC, oscillator and helical resonator should
not be difficult to fabricate since the layout is fairly simple.

I have been looking for the time to lay out a
board myself, since I have most of the
components, but the time has been illusive and I
haven't gotten it done yet. I just started doing
kits for the N2PK VNA, which is a major time
sink, so the outlook for finding teh time for the
DDS clock generator looks poor (in the immediate future).

Regards,

Art


>With the release of the AD9912 DDS there has been a surge of
>interest for a good 1Ghz clock source.
>Not fully understanding the issues, would the proposal below be
>worth experimenting with?
>
>Crystek have recently introduced a new VCO – CVCO55CX-1000-1000, the
>performance specs look
>pretty good to me. If this was phase lock looped to a 10Mhz GPS,
>would this be sufficient
>as a clock for the AD9912.
>
>10Mhz --- Phase det --- Diff Amp --- VCO -- Buffer Amp --- 1Ghz out
>
1654 2008-05-23 09:28:46 Weddig, Henning-C... Re: [SPAM] [emrfd] AD9912 DDS clock source – just a thought?
Kevin,

i have a lot of (bad) experience with Hittite chips.
In general ECL chips are limited in phase noise, the floor is about -150
dBc.
I have also tried the HMC439 in a phase detector, not getting the result
as I expected and the data sheet proposed!

A better solution: use one (or two) AD9515 clock dsitribution chips from
Analog devices having a phase noise floor of about -160dBc/Hz (division
rate 10 each) for the programmable divider of the 1 GHz clock and a
"normal phase frequency detector using the a 7474 type of D-FF.
Even dividing 100 MHz down to 10 MHz You could use some of these fast
Fairchild single gate D-FF´s 8and even for the PD)

Henning
DK5LV

Kevin Wheatley schrieb:

> ------------------------------------------------------------------------
>
> Betreff:
> [emrfd] AD9912 DDS clock source – just a thought?
> Von:
> "Kevin Wheatley" <m0khz@tiscali.co.uk>
> Datum:
> Fri, 23 May 2008 08:32:25 -0000
> An:
> emrfd@yahoogroups.com
>
> An:
> emrfd@yahoogroups.com
>
>
> With the release of the AD9912 DDS there has been a surge of
> interest for a good 1Ghz clock source.
> Not fully understanding the issues, would the proposal below be
> worth experimenting with?
>
> Crystek have recently introduced a new VCO – CVCO55CX-1000-1000, the
> performance specs look
> pretty good to me. If this was phase lock looped to a 10Mhz GPS,
> would this be sufficient
> as a clock for the AD9912.
>
> 10Mhz --- Phase det --- Diff Amp --- VCO -- Buffer Amp --- 1Ghz out
>