--- On Sat, 1/8/11, Magnus Danielson <mag...@rubidium.dyndns.org> wrote:
... > >> How will the input side work? How will you handle > input > >> signals of various kinds? In particular sine of > various > >> amplitudes and frequencies. Slew-rate can be a > limiting > >> factor as white noise will convert into jitter if > hitting a > >> straight comparator. Choice of trigger point can > be done to > >> achieve lowest jitter, so just AC-blocking and > trigger on > >> the 0V may not be the best solution if shape is > not well > >> known. Noise of input stage comes into play. > > > > > > I am glad you asked. :) This is still one big To Be > Determined at this point. > > > > As you say, the choice of trigger point has a large > impact on jitter. Do you have any suggestions on how to > achieve this? Either for the situation where the signal > shape is well known or not so well known. > > > > ... > > Well, you do have comparators and programmable trigger > level. There is > no magic to that side. But do care about bandwidth. It > might be needed > to actually not use a comparator up-front but rather let > there be one or > two stages of gain, where the first one DC-shifts the > signal with the > trigger level. This way you gain yourself to a higher > slew-rate. This is > really what Collins-style ZCD do. The trick is to balance > the gain and > noise-bandwidths such that you get optimum slew-rate > bandwidth for > lowest added noise. Magnus, thanks for your reply. The Collin's style ZCD was a useful hint. Didn't know that one yet. I read up on it on Bruce's site. At least I think it is Bruce's site, what with the "/~bruce/" in the url. ;) Especially the bit about the Generalised Collins Hard Limiter. Checked the paper, looks useful ... at a later date (it's on the list for rev 3 now). For now I have decided to keep the analog frontend as simple as I can get away with. Which in essence ranges from "nothing at all, straight up connect, better make sure what you connect is LVCMOS25/33 or LVPECL25/33" to "comparator + DAC, and just learn to live with the extra jitter until a later revision". regards, Fred _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.