[time-nuts] SI5328

Chris Caudle chris at chriscaudle.org
Mon Jan 22 09:18:29 EST 2018


On Mon, January 22, 2018 6:42 am, Hal Murray wrote:
> Does anybody know what's in the DSPLL box?

Basically a PLL implemented with some kind of DDS for the VCO and DSP for
the loop filter.

https://www.silabs.com/documents/public/white-papers/Silicon-Labs-Next-Generation-DSPLL-Technology-White-Paper---June-2015.pdf

The DSP loop filter gives a really wide range of loop bandwidth, down to
fractional Hz for some parts.  Using a DDS for the VCO gives a lot of
flexibility in output frequency selection, but means that there can be
problems with  spurs.  Part of the SiLabs secret sauce is supposed to
reduce spurs compared to a simpler NCO implementation, but I don't think
you can eliminate spurs entirely with any kind of DDS based design.

-- 
Chris Caudle







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