[time-nuts] More on SiLabs 5340

Bob kb8tq kb8tq at n1k.org
Mon Jan 29 16:32:11 EST 2018


Hi

There may be “tweaks” to get the noise shaping working better on the 10 MHz input. Some PLL
chips have pre-multipliers for the reference to improve things…. the magic apparently works better
with a fast input …(and yes, there are good reasons why)

Bob

> On Jan 29, 2018, at 3:38 PM, John Ackermann N8UR <jra at febo.com> wrote:
> 
> I'm slowly learning how these ultra-low-jitter clock generators work. Yesterday I posted some phase noise results in "free run" mode where the 48 MHz crystal on the evaluation board was the only reference.
> 
> Today I tried replacing the crystal with a 10 MHz input, and found that the evaluation board requires surgery to support that.  What I was able to do, though, was feed 10 MHz into the "Input 0" port which apparently disciplines the free-running crystal.  I used a 10811A fed into a T2-Mini with divider removed, so all it does is provide the Wenzel squaring circuit.  Results attached, added to the plots from yesterday. Also attached is an ADEV plot proving that the 10 MHz is in control.
> 
> The close-in phase noise is quite amazing, but the floor is much worse than in free-run mode.  This was a very hay-wire experiment, so there are lots of things that could be suboptimal.  It sure would be nice to get the best of both those plots!
> 
> John
> <siLabs5340-test-2-adev.png><siLabs5340-test-2.png>_______________________________________________
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