[time-nuts] Digital Mixing with a BeagleBone Black and D Flip Flop

pablo alvarez pabloalvarezsanchez at gmail.com
Mon Nov 24 06:59:12 EST 2014

> The current implementation used in WR was developed by Tomasz
> Wlostowski in the frame of his MSc thesis, following the ideas of
> Pablo Alvarez which Bruce pointed to earlier. As you can see in
> Tomasz's dissertation [1], there was not a lot of investigation on
> optimal strategies for DDTMD noise. The precision at the time was
> deemed more than adequate. It is very timely that you bring up this
> subject now, because I hope to start looking at ways to optimize phase
> noise in WR in the coming months, and noise coming from the DDMTD
> phase detector is definitely something I want to look at. I will be
> very interested in your ideas and findings regarding optimal
> strategies for the de-glitcher.

Hi Simon and Javier,

I arrive late to this discussion but I would like to add my grain of salt.
As Javier says there was not a detailed optimization of the DDMTD
architecture as jitter was already limited by all the surrounding
electronics. I would like to add that much of the noise rejection is due to
the implementation of a median estimator for the incoming edge position
respect to the "slightly-offset" oscillator. It is easy and fun to proof
that this median estimator can be implemented with a counter counting the
number of sampled zeros and a simple state machine state machine that
places counter start in a safe zone. In fact, when you think it out, the
most curious thing is that this algorithm is nothing more than a sort of
generalization of the bang-bang architecture to measure phase offsets.



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