[SI-LIST] Re: Jitter measurement floor on different high bandwidth oscilloscopes
- From: "T.K. Jeon" <tkjeon@xxxxxxxxxxx>
- To: "Alfred P. Neves" <al@xxxxxxxxxxxxx>
- Date: Thu, 10 Jun 2010 18:30:14 -0700
I guess that using a spectrum analyzer is one of the good ideas to benchmark
jitter packages, especially, for PJ-RJ separation.
I noticed that some postprocessing algorithms show poor performance to separate
PJ and RJ effectively when the source is clock-like(1010) signal. In other
words, when there is a spectral peak from the signal spectrum, which should
correspond to PJ, a jitter package could fail to take that for PJ calculation.
The phase noise at a spectral peak can be easily obtained without any special
tools. In order to compute phase noise from signal spectrum, you can read X dB
on the peak in the sideband using the marker, and then you will need to
subtract noise power bandwidth, which is usually 1.2*RBW(Resolution Bandwidth).
Furthermore, a correction factor (roughly 2.5dB for Agilent spectrum analyzer)
should be added for noise distribution.
Regards,
TK
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Alfred P. Neves
Sent: Thursday, June 10, 2010 10:02 AM
To: 'steve weir'; 'Heyfitch'
Cc: si-list@xxxxxxxxxxxxx; 'prasad'
Subject: [SI-LIST] Re: Jitter measurement floor on different high bandwidth
oscilloscopes
I believe benchmarking an oscilloscope/jitter package jitter performance
needs to be addressed in relation to the specification and work your
addressing.
We conducted jitter benchmark years ago on both sampling and real time
scopes doing the following:
1. sweep a very low phase noise sine wave source over fveryhigh down to
10MHz and measure the single period jitter, plot it in Excel. Using a Rhode
Shwartz generator, with very good phase noise, we estimated the time domain
jitter using phase noise and simple equations in Excel (our estimates were
that period jitter was typically down into the sub 100's of femtoseconds).
Keep the input signal at full scale of scope input, say +-1V. Histogram
each jitter measurement, and separate out RJ-DJ using the relevant jitter
package.
2. Repeat above using 10dB successive attenuation down to about 10mV input
signal from +-1V input.
3. Repeat above 1. but measure Phase Noise, or accumulated time jitter
over multiple periods (step one was period jitter only, here we measure the
jitter of nT cycles). Mike Li's book explains relationship between period
and phase jitter btw.
Some scopes maintain very good period jitter but have high accumulated time
base error which is picked up by making phase noise jitter, or multiple
period accumulated jitter measurements. This is a critical issue,
depending on your jitter characterization requirements.
The dV/dt of the sine wave source directly changes with frequency, so this
is a good test of the scopes referred input noise and input sensitivity as
discussed in earlier post.
Period measurements are very useful for high speed memory, mixed signal so
that base is covered, whereas Phase Jitter is more applicable to NRZ data
standards (10G Eth, FC, XAUI, PCIExpress, etc.,).
Aside: A sore spot for all the instrument folks is separation of BUJ,
bounded uncorrelated jitter, from RJ-DJ. This, IMHO, is more of a function
of the jitter package separation capabilities. To my knowledge, I have not
seen any studies suggesting algorithmic limitations based on pattern type
(PRBS versus coded patterns) or length and ability to separate out BUJ. We
don't deal with the problem directly, in that we compliment our jitter
analysis with 3D solver and TDR/VNA measurements to show differential
coupling, creating a model of the channel.
Alfred P. Neves <*)))))><{
Hillsboro Office:
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of Teraspeed Consulting Group LLC
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Thursday, June 10, 2010 9:24 AM
To: Heyfitch
Cc: si-list@xxxxxxxxxxxxx; prasad
Subject: [SI-LIST] Re: Jitter measurement floor on different high bandwidth
oscilloscopes
This is why before coughing over the price of a condo for a scope and
probes you really need to evaluate instruments like these on your own
turf with a test set-up you fully understand. The investment in probes
alone is going to have a strong influence on purchases for many years.
As the Templar Knight said: "Choose wisely."
Steve.
Heyfitch wrote:
> Agilent's app note 1491 (5989-0553EN.pdf) illustrates the points Steve
made
> below. (Never mind that it is written by Agilent and naturally shows that
> Agilent's solution is "far superior" to Tektronix' one.)
> - Vadim
>
>
> On Wed, Jun 9, 2010 at 11:49 PM, steve weir <weirsi@xxxxxxxxxx> wrote:
>
>
>> 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
>> 150 N. Center St. #211
>> Reno, NV 89501
>> www.ipblox.com
>>
>> (775) 299-4236 Business
>> (866) 675-4630 Toll-free
>> (707) 780-1951 Fax
>>
>>
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>
>
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--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
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