life speed wrote:
Hello Time Nuts,
I'm back again. I designed bandwidth-limited (30 MHz) ADA4899-1 opamp circuits
to buffer the 10 MHz reference, with theoretical noise of less than 3 nV/rtHz.
Oscillator noise is about -155 dBc/rtHz from 1 KHz to 10 KHz, and -160 dBc/rtHz
from 10 KHz to 100 KHz. Unfortunately the rest of the design is holding up PCB
manufacture, so results on these won't be available for awhile.
Which brings me to the other design-stopping considerations: Is anybody aware
of low-noise analog switches that can be used to reconfigure the 10 MHz
reference paths without significantly degrading the phase noise? As always, I
believe 1/F noise would be the concern. Non-reflective is great, but I can
accomplish that by using more switches and 50 ohm resistors if need be.
Isolation is a key consideration as well. Mechanical relays are out of the
question.
An alternative to switching is phase-locking the OCXO to an external reference.
I have thoroughly looked into this possibility, and it is likely my preferred
approach. But I need to understand how the switching approach compares, hence
my question. I do not need help with phase-locking; this feature is readily
available from OCXO vendors who have dedicated years of research to optimizing
their products.
Any switch experience out there?
Why would flicker noise be a concern if there is no dc current flowing
in the switches?
Bruce
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