[SI-LIST] Re: jitter measurements on clock

  • From: Chris Cheng <Chris.Cheng@xxxxxxxx>
  • To: steve weir <weirsi@xxxxxxxxxx>, prasad <hariprasad.palli@xxxxxxxxx>
  • Date: Fri, 13 Aug 2010 17:45:31 -0700

I agree we need to be careful about interpreting Rj data from scope software 
such as EzJIT.
Chances are your clock source is generated from a PLL and your receiving chip 
is also a PLL.
You need to at least input your receiving PLL loop bandwidth to EzJIT type of 
software.
Jitter transfer is a function of your PLL loop bandwidth and the effective Rj 
after passing the ideal PLL is also dependent on the loop bandwidth.
And if your receiver PLL bandwidth dropped below the reference clock PLL loop 
bandwidth, the Tj together with your Pj will grow.
Chris

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On 
Behalf Of steve weir
Sent: Thursday, August 12, 2010 1:40 PM
To: prasad
Cc: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: jitter measurements on clock

Prasad, what you do depends on what you want to know.  Before worrying
so much about which buttons to push in the software, I think you need to
clearly establish your goals.

Do you want to know if the clock really meets its specification?  Then
you need to reproduce equivalent test conditions and measurement
extraction as used by the clock manufacturer.

Do you want to inspect incoming parts?  Then you can less rigorous
testing and extraction.

Do you want to compare clocks from different manufacturers to make
product selection?  Then you need to not only test to the vendor spec,
but qualify the clock under the conditions you wish to apply it.


Steve.
prasad wrote:
> hi all,
> thank you very much for your suggestions.
>
> from all the discussions , what i understand is ,
>
> 1.clock signal  is assumed to have very negligible determinsitc jitter
> 2. Manufacturers always specify the RJ of the same
>
>
> if i need to verify this spec , i need to measure the TIE  RMS (AC) or use
> the RJ and DJ separation wizard to extract the RJ value verify.
>
>
> please comment.
>
>
> once again thank you very much for all your inputs.
>
>
> Best Regards,
> hari.
>
> On 13 August 2010 00:02, T.K. Jeon <tkjeon@xxxxxxxxxxx> wrote:
>
>
>> Hi Hari,
>>
>> Simply taking the rms value of TIE won't give you random jitter. For better
>> measurement, you should subtract the average TIE from your real time TIE,
>> and take AC rms value of the resulted value. This would give you more
>> accurate value than the rms of the real time TIE. However, the final value
>> by using this way is not pure random jitter, i.e. it includes RJ plus
>> uncorrelated PJ. Therefore, you should use other technique to separate the
>> PJ component from your TIE measurement.
>>
>> Regards,
>> TK
>>
>> -----Original Message-----
>> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
>> On Behalf Of prasad
>> Sent: Wednesday, August 11, 2010 10:34 AM
>> To: si-list@xxxxxxxxxxxxx
>> Subject: [SI-LIST] jitter measurements on clock
>>
>>  hi All,
>> normally when we look at the data sheets of a clock signal for the jitter
>> number, they usually specify it a RMS jitter.
>>
>> i understand from the basics that , only random jitter is quantified as
>> RMS.
>> i am not sure why there is only random jitter in the clock. is the
>> Deterministic component is negligible?
>>
>> in that case, using our EzJIT plus software, if i want to measure this spec
>> of a the clock, what would be my measurement?
>>
>> is it ok, if i measure the TIE of the clock and take the RMS of the TIE
>> trend?
>>
>>
>> thanks,
>> hari
>>
>>
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