[time-nuts] ADF4002 phase noise - in FireFly-IIA-100MHz

SAIDJACK at aol.com SAIDJACK at aol.com
Tue Mar 9 23:28:00 UTC 2010


Hi John,
 
we have a new 100MHz board (FireFly-IIA-100MHz) that uses an ADF4002 to  
generate 100MHz from the 10MHz internal OCXO.
 
The VCXO we use is rated at better than 100dBc at 100Hz.
 
The 10MHz reference achieves typ. -148 dBc at 100Hz.
 
We measured -115dBc/Hz at 100MHz at 100Hz offset in a couple of sample  
units using the TSC5125A.
 
This is in-line with your measurement at 80MHz.
 
Loop BW is ~30Hz, so the 100Hz offset is slightly outside of the  ADF4002 
loop BW.
 
Note that we get ~15dB better performance at 100Hz offset than the VCXO  
datasheet would let us expect.
 
bye,
Said
 
 
In a message dated 3/9/2010 14:00:16 Pacific Standard Time, jmiles at pop.net  
writes:

I  haven't exhaustively tested the ADF4107 but I have played with the  
ADF4002
recently.  I haven't been able to come within several dBc/Hz  of its rated
noise level.  In one test, at 100 Hz from an 80 MHz  carrier, I've seen
about -118 dBc/Hz from the ADF4002 when fed by 10 MHz  with -145 dBc/Hz at
100 Hz (which would become about -127 dBc/Hz in an  ideal 80 MHz 
multiplier.)
The figure-of-merit equation suggests that -222 +  20*log(8) + 10*log(10 
MHz)
= -134 dBc/Hz would be achievable, well below  the -127 dBc/Hz limit imposed
by the  reference.


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