[SI-LIST] Re: Jitter measurement floor on different high bandwidth oscilloscopes
- From: wolfgang.maichen@xxxxxxxxxxxx
- To: prasad <hariprasad.palli@xxxxxxxxx>
- Date: Wed, 9 Jun 2010 23:34:24 -0700
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>
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[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
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