[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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