Hello Vadim, you are right, RMS assumes the two contributions are uncorrelated. For scope sample time jitter and ADC (and amplifier chain) input noise this is probably a pretty good assumption, but depending on the design of a particular scope there could of course be some correlation or anticorrelation. E.g. both could be caused by noise on the power supply to the sampling circuitry (and that noise could be non-Gaussian e.g. if caused by a switching power supply). That's one reason I tried to caution right away that in a short post one can only scratch the surface. I did not intend to imply that pure timing jitter and voltage noise jitter always add up that way. As far as ISI (data dependent) jitter is concerned, personally I normally consider it voltage noise translated to jitter, if one broadens the meaning of noise to "voltage deviation from the 'normal' waveform". RMS addition rests on the assumption that both contributors are not only independent of each other, but also that both have Gaussian distribution. Especially the latter assumption can only be a more or less crude approximation for ISI since ISI always comes from a limited number of preceding bits. In an eye diagram ISI shows up as discrete bands of transitions, whereas random jitter causes continuous broadening of the transitions. The mathematically sound approach is of course convolution of all jitter contributors (this still assumes independence of the jitter contributors, as well as linearity of the system, so is not universally applicable either), and RMS summation is simply the convolution result for two Gaussian distributions. Wolfgang Heyfitch <heyfitch@xxxxxxxx> Sent by: si-list-bounce@xxxxxxxxxxxxx 06/10/2010 08:31 AM To wolfgang.maichen@xxxxxxxxxxxx cc prasad <hariprasad.palli@xxxxxxxxx>, si-list@xxxxxxxxxxxxx, si-list-bounce@xxxxxxxxxxxxx Subject [SI-LIST] Re: Jitter measurement floor on different high bandwidth oscilloscopes Wolfgang, you stated that the pure timing jitter and translated voltage noise jitter add up in RMS fashion. This would imply that the two are completely uncorrelated. Is this always true? What comes to my mind is the ISI jitter of a non-clock (i.e. non-periodic) signal caused by a band-limited channel. Would such jitter be interpreted as voltage or timing jitter or a combination of both? If the latter, would the pure timing and voltage components be considered uncorrelated? Thanks. Vadim Heyfitch On Thu, Jun 10, 2010 at 1:34 AM, <wolfgang.maichen@xxxxxxxxxxxx> wrote: > Hello Prasad > jitter performance analysis of high-end scopes is decidedly non-trivial, > but to get you started: > > As for random jitter measurement floor, there are three parameters that > are important: > > (1) the scopes sample clock jitter (i.e. when the samples are actually > taken vs. their ideal position) > (2) the sampler's noise > (3) the signal's slew rate > > The measured random jitter can be thought of two components, first pure > random timing jitter, second noise that gets translated into timing > jitter. A perfectly noise-free signal (and noise-free scope) can still > show random timing jitter. On the other hand, noise on the signal (or in > the sampling circuit) always gets translated into timing jitter, equal to > voltage noise divided by the slew rate. So a large and/or very fast rising > signal (corresponding to a large slew rate) will be less affected by a > given amount of noise than a signal with slow slew rate, but the effect > will never be zero. Both components (pure timing jitter and translated > voltage noise) add up in RMS fashion. > > So if you have two scopes, one (A) with low jitter floor (sampling timing > jitter) but high noise floor, and another (B) with high jitter floor but > low noise floor), it can depend on the signal to be measured which one > will produce the lower measured jitter number. If the signal has a high > slew rate (making it less sensitive to noise) then scope (A) has an > advantage, otherwise scope (B). So in reference to your question which is > better, the answer is the common "it depends", in this case it depends on > the signal's slew rate. > > Wolfgang > > > > > > > > prasad <hariprasad.palli@xxxxxxxxx> > Sent by: si-list-bounce@xxxxxxxxxxxxx > 06/09/2010 08:57 PM > > To > si-list@xxxxxxxxxxxxx > cc > > Subject > [SI-LIST] Jitter measurement floor on different high bandwidth > oscilloscopes > > > > > > > Hi every one.... > > i am evaluating high bandwidth oscilloscopes (12GHz) from different > vendors. I was looking the data sheets of them. One of the > them(DSO91204A) has very good noise floor compared to others. Though > its a good thing for me but when it comes to the jitter measurements , > the lowest jitter that can be measured on that is dependatnt on the > slew rate of the signal ,which is actually true(since the voltage > noise will have a second order effect on the timing of the signal). > But when i looked at one more vendor (SDA13Zi) the noise floor is poor > compared to other. In which case the lowest jitter that can be > measured (jitter measurement floor)should be higher than earlier. But > if you look at the datasheet, they have specified a fixed value for > this which is very less . > My question is , if the noise floor is high in the second box how > would the jitter measurement floor be less? > second one is , since the timing noise(jitter) is dependatnt on slew > rate, how a fixed value is given in datasheet? > > > please help me understand. Am i missing some other factor here? > Welcome all your suggestions and ideas... > > > thanks in advance... > prasad > > h > > On 09/06/2010, colin_warwick@xxxxxxxxxxx <colin_warwick@xxxxxxxxxxx> > wrote: > > (Note: I sent this info to Hermann off-list but he suggested it might be > of > > general interest. Send flames to me, not Hermann, if it isn't.) > > > > In ADS the implementation is: > > > > > > "Fast" corner > > (a) the max values are selected for all the I-V data (Pullup, Pulldown, > > Power Clamp a Ground Clamp) and for the waveform data (Ramp, Rising > Waveform > > and Falling Waveform), and > > (b) the min values are selected for all R, L, C, delay and TT data. > > > > > > "Slow" corner is the reverse obviously > > (a) the min values are selected for all the I-V data (Pullup, Pulldown, > > Power Clamp a Ground Clamp) and for the waveform data (Ramp, Rising > Waveform > > and Falling Waveform), and > > (b) the max values are selected for all R, L, C, delay and TT data. > > > > > > > > -- Colin > > > > -----Original Message----- > > . > > . > > . > > > > Any feedback from the tool vendors how they implemented this selection ? > > > > Thanks and Regards > > > > Hermann > > > > EKH - EyeKnowHow > > Hermann Ruckerbauer > > www.EyeKnowHow.de > > Hermann.Ruckerbauer@xxxxxxxxxxxxx > > Veilchenstrasse 1 > > 94554 Moos > > Tel.: +49 (0)9938 / 902 083 > > Mobile: +49 (0)176 / 787 787 77 > > Fax: +49 (0)3212 / 121 9008 > > ------------------------------------------------------------------ > > To unsubscribe from si-list: > > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > > > or to administer your membership from a web page, go to: > > //www.freelists.org/webpage/si-list > > > > For help: > > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > > > > List technical documents are available at: > > http://www.si-list.net > > > > List archives are viewable at: > > //www.freelists.org/archives/si-list > > > > Old (prior to June 6, 2001) list archives are viewable at: > > http://www.qsl.net/wb6tpu > > > > > > > > -- > Sent from my mobile device > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > > List technical documents are available at: > http://www.si-list.net > > List archives are viewable at: > //www.freelists.org/archives/si-list > > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > > ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu