On Tuesday, June 16, 2015 10:01:09 AM Attila Kinali wrote: > Hoi Bruce, > > On Tue, 16 Jun 2015 12:24:34 +1200 > > Bruce Griffiths <bruce.griffi...@xtra.co.nz> wrote: > > Using an ADC to sample a triggered damped sinewave easily achieves 5ps > > resolution (eg Keysight Acquiris). With a better optimised waveform model > > and least squares fitting routine greater resolution is feasible. > > The accuracy is dependent on the ADC sampling clock stability. > > An optical frequency standard derived clock may be required to maintain > > ps accuracy for long time intervals. > > Do you mean the technique that Panek et al. [1] are using? Not quite he used an impulse to excite a saw filter rather than switching off the dc current feed to an inductor or the equivalent. > IIRC he got that down to 0.5ps RMS now. And yes, the major > source of error is the oscillator, according to [2]. > Ripamonti et al. showed in [3] that using an LC tank instead of an SAW > filter will result in something in the order of 2-10ps RMS (after > temperature compensation). So this system is in the same region as an well > designed time-to-amplitude converter based system. > The curve fitting algorithm they used is somewhat deficient as is the switching method employed one can do much better provided one has sufficient time or computing resources available. My crude testing using a somewhat simplified diode switched current source powered by the signal itself achieved a fitting noise of around 5ps with a 14 bit ADC. A better driver and higher resolution ADC with a lower noise input amplifier than the input amplifier of the oscilloscope I used should improve the results somewhat as would a better model for the damped sine signal. > I really wonder which one would be easier to build. Keysight as far as I can tell used a discrete LC circuit to produce a damped sine wave rather than the conventional TAC approach used in the lower resolution Acquiris models. Bruce > > Attila Kinali > > > [1] "Time interval measurement device based on surface acoustic wave filter > excitation, providing 1ps precision and stability", by Panek andProchazka, > 2007 http://dx.doi.org/10.1063/1.2779217 > > [2] "Random Errors in Time Interval Measurement Based on SAW Filter > Excitation", by Panek, 2008 > http://dx.doi.org/10.1109/TIM.2007.915465 > > [3] "High frequency, high time resolution time-to-digital converter > employing passive resonating circuits", by Ripamonti, Abba, Geraci, 2010 > http://dx.doi.org/10.1063/1.3432002
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