[SI-LIST] Re: Jitter measurement floor on different high bandwidth oscilloscopes
- From: steve weir <weirsi@xxxxxxxxxx>
- To: prasad <hariprasad.palli@xxxxxxxxx>
- Date: Wed, 09 Jun 2010 21:49:14 -0700
Be wary of specifications and marketing hype and FUD. Modern scopes are
very dependent on the signal processing: analog and especially digital.
Where one vendor claims advantage in slew rate another claims advantage
in noise floor. Overactive DSP algorithms have been seen in various
scopes that create waveform artifacts that are not real. I've gone
through considerable pain with customers whose scopes were lying to
them, where we had to set-up experiments with better behaved instruments
in order to get them to see the truth. You want to know that if you
follow good measurement practice that what your scope tells you is
faithful, and not a DSP induced fantasy.
Claims are all find and good, but for the kind of money that you are
spending, you owe it to yourself to have each vendor come in with their
scopes and put them through paces with a clock / pulse generator that
you supply in probing configurations that you set-up as representative
of the type of work you expect to do.
The other thing that you should take into careful account is that modern
scopes represent an investment in probes that is often similar to the
price of the scope itself. It is just as important to evaluate the
probes: How they perform, do they meet your physical access needs, how
much do replacement supplies cost for things like solder ins cost, what
probes are you already invested as anything else about the scope.
Steve.
prasad wrote:
> 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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>>
>
>
--
Steve Weir
IPBLOX, LLC
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