Thanks Pablo.
I've been finding that my implementation is a very good noise detector
(in all kinds of fun ways) and my most recent effort has been at the
hardware level in better layout, shielding and in reducing the number of
noise sources.
The impact of non-random noise is that transitions near an edge get
quantised to the noise source, particularly the first and last
transitions of a set. This leads to some of the simpler edge detection
algorithms perfoming very poorly as they carry through this quantisation.
Clearly, the cleaner the hardware implementation the less impact
external noise will be until, hopefully, it is below requirements. At
some point though I may get to a hardware/software tradeoff where the
cost of reducing noise via hardware becomes more expensive than a
complex edge detection algorithm that could remove the noise in software
instead.
Of course, everyone will have their own definition of what 'cost' and
'more expensive' means but in my case software solutions are relatively
cheap as I'm using a general purpose processor rather than FPGA.
Cheers
Simon
On 24/11/2014 11:59, pablo alvarez wrote:
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.
Cheers,
Pablo
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