Hi Naresh, Steve described in details many reasons why receiver might see a noise when you applied in-phase noise to Vss and Vcc. It is also important to know some more details about your experiments to make a conclusion. Whether you were using oscilloscope, or receiver to measure output jitter and noise, and how you applied noise to Vss and Vcc. In addition to Steve observation, different "modulation sensitivity" of Vss and Vcc,  the pre-driver to the jitter contribution, and just simple conversion of waveform' shift to the jitter, - all might contribute to the output jitter and noise. I agree with you that I/O delay respect to the Vss "disturbance" also one of the reason of remaining noise.   I also agree with you that it is good to extract both Vss and Vcc respect to ideal reference, which is not so easy to simulate. However, if you can, there is even more important reason to do so. If you have other signals switching along with you measured, these others will contribute through common Vss to the Vss noise. So, all depends on details how you applied noise and did measurements. Thank you.Iliya On Tuesday, October 7, 2014 11:50 PM, Naresh Dhamija <naresh.dhamija@xxxxxxxxxxxxx> wrote: Hi Iliya, I understand that different blocks inside IO will convert the in phase noise to differential noise and will cause jitter within the IO, but at the output of IO pad w.r.t noise vss, I see some noise, I guess it is because of finite delay within the output stage of IO . Is this correct? If it is so, then my follow up question is: In the complete system simulation, when we plug package and board s-parameter models, it is good to have both vddio and vss extracted w.r.t ideal ground rather than only vddio extracted which will only have differential noise of vddio with its local vss where common noise of vddio and vss is missed out. Regards Naresh *From:* Iliya Zamek [mailto:i_zamek@xxxxxxxxx] *Sent:* Wednesday, October 08, 2014 12:38 AM *To:* naresh.dhamija@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx *Subject:* Re: [SI-LIST] Single ended Noise OR Differential Noise Hi Naresh, Your observation is correct. The impact of PDN noise on on-chip signals timing and logic levels noise is different. The impact on I/O Jitter is more complex. The impact on logic levels' noise does not depend on noise frequency and I/O signal frequency interrelationship, but impact on I/O' Jitter does. You might want to see the results of research of impact noise on Jitter in a paper (and references) by Google: "On-chip Jitter and system Power Integrity", I. Zamek, Designcon 2012 Also, there are two effects to consider at I/O Jitter analysis: impact on Pre-Driver and impact on output Buffer. Impact on Pre-Driver contribute mainly on Jitter, the impact on Buffer contributes on both, Jitter and Logic levels' noise. You might see the research and experiments on I/O jitter in reference #16: Zhe Li, Iliya Zamek, Peter Boyle, âFPGA IO Timing Variations with SSO Noise,â DesignCon 2008 Thank you. Iliya Zamek On Tuesday, October 7, 2014 6:10 AM, Naresh Dhamija < naresh.dhamija@xxxxxxxxxxxxx> wrote: Hi folks, I am doing power noise analysis on a system that uses SSTL IO buffers. I am seeing the ripple on the IO output signal - such that during hi state IO output signal follows the noise whatever is on the vddio and during low state, IO output signal follows the noise on the vss. Observing this phenomenon, I purposely forced IN PHASE single ended noise to both vdddio and vss of almost the same frequency as of data rate but uncorrelated with data rate. Since noise forced to vddio and vss are IN PHASE so Differential Noise measured between vddio and vss at each instant shows zero noise. But still I see jitter on the edges because of finite rise and fall times, the initial low level and final high level for a transition from low to hi are not always same. Does this mean that along with differential noise, single ended noise on power and ground also cause jitter to IO driver. Regards Naresh ------------------------------------------------------------------ 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 forum is accessible at:        http://tech.groups.yahoo.com/group/si-list 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 forum is accessible at:        http://tech.groups.yahoo.com/group/si-list 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list 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