Hi Glitches are not very likely in a capacitor charge setup. FPGA TDC's have a lot of them. The "easy" way to find out you have a problem is to run multiple gizmos on the same set of inputs. Knowing you have a problem isn't always the same as *solving* the problem ….
Bob On Dec 28, 2012, at 1:53 PM, Bruce Griffiths <[email protected]> wrote: > One potential source of non monotonicity is the ADC particularly those > embedded in a microprocessor. > The only cure being to either use an external ADC that is monotonic or > truncate the ADC result until it's monotonic. > > Varying the synchroniser clock frequency (a 2:1 range should suffice to > cover the range of interest) should allow non monotonic behaviour to be > detected. > Otherwise one has to resort to using calibrated delay lines. > > Bruce > > Bob Camp wrote: >> Hi >> >> The statistical fill approach is a cute way to go. The gotcha comes in when >> you have a structure that *may* not be monotonic. >> >> Bob >> >> On Dec 28, 2012, at 1:04 PM, Bruce Griffiths<[email protected]> >> wrote: >> >> >>> Fabio Eboli wrote: >>> >>>> Hello >>>> >>>> How could I test the time to analog converter >>>> we talked few posts ago? >>>> Something that can be done with things I have >>>> or can easily find. >>>> >>> One method is to use a statistical fill the buckets technique to measure >>> the linearity. >>> To do this one needs to use an incoherent source to trigger the >>> interpolator and plot a histogram of the results. >>> A noisy RC oscillator would be useful for this but care should be taken to >>> avoid injection locking. >>> To achieve useful measurement in a reasonable time interval a trigger rate >>> somewhat greater than 1Hz is required. >>> If the interpolator has 1024 time delay bins then ~ 100,000 trigger events >>> are required to achieve a bin width measurement error of 10%. >>> >>> Otherwise a series of measurements of a set of accurately known delays is >>> required. >>> Useful results can be produced by measuring the delay between various >>> outputs of a shift register clocked at a sequence of different measured >>> frequencies. >>> >>>> I was thinking that would be nice to try to >>>> feed it with signals similar to the real ones, >>>> but that can be controlled: PPS + 10MHz reference, >>>> without the PPS tipical jitter. >>>> >>>> >>> One should characterise the interpolator linearity etc first. >>> >>>> To do so I was thinking to use the PPS from >>>> one of the 2 FE5680 and the 10MHz from the >>>> second ad use these to simulate the real signals. >>>> >>>> I can tune the frequency of the Rb with the >>>> serial interface (tested and working). >>>> I'd like to verify both the resolution and >>>> repeteability. >>>> >>>> I was trying to figure the approx jitter >>>> I will have using the Rb like I said above, >>>> so I'm giving an eye to this diagram from >>>> John Miles page: http://www.ke5fx.com/rb.htm >>>> >>>> If I'm understanding correctly, that 5680 >>>> at 1s should have most of the jitter (95% +-2sigma) >>>> into an interval +- 3.08x10^-11 wide, i.e. about 62pS >>>> on the PPS signal (non considering the PPS buffer >>>> inside the 5680). Is this how it work, or I'm mistaking? >>>> This is from only one unit, but both unit will have >>>> the jitter, how to take into account the jitter >>>> from both? >>>> >>>> Is there a better method to make this test? >>>> I could try to test the TAC alone feeding it >>>> with a 100 to 200nS pulse, but I dont know >>>> from where to start to generate a clean stable >>>> and repeteable pulse. >>>> >>>> >>> You dont need one (see above) as long as you have the means to accumulate >>> the results of 100,000 measurements or preferably more. >>> >>>> I have the 2 5680, the counter with it's 10MHz >>>> inputs and outpus, and a Vectron OCXO that came >>>> with one of the 5680, with these markings: >>>> OCXO500-18 63.897600MHz >>>> 34537 A0715 >>>> and... >>>> soldering iron, solder and scrap electronics :) >>>> >>>> Thanks, >>>> Fabio. >>>> >>>> >>> Bruce >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >>> >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> >> > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
