Hello Canes - Since you're measuring noise at a quiet node, I assume you are discussing SSO noise. I'm going to step out a little here and make a bold statement : if you are comparing the SSO characteristics of two different technologies, say 2.5V LVTTL and 2.5V SSTL, and their rise times are the same, and their source impedances are the same, then their SSO noise will also be the same. So, based on that statement, changes in these above mentioned items will cause the SSO to change. If you go to a stronger driver or a larger voltage swing (3.3V LVTTL) - and the rise time stays the same - then you've increased SSO noise. If you go with a weaker driver, or you put a series resistor at the output (like SSTL) then the SSO noise will decrease. Signal swing, rise/fall time, and source-Z are the things that influence SSO noise. As a side note, you mention "12ma driver". IC manufacturers use this as a DC drive number not an AC number. That's why we should use the source impedance of the driver as a better (but not perfect) description of a driver's capability.=20 Regards, Jim Peterson Honeywell -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Canes Venatici Sent: Monday, April 30, 2007 1:18 AM To: si-list@xxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] SSO SSTL Vs LVTTL Hi, I did quite node simulations in LVTTL and SSTL class I and II pads. I used transmission line models for all the=20 simulations with noise measured at the Far End. I tried to operate the LVTTL pads at 3.3V with 12mA drive strength. I could see the noise is more than with SSTL2-I/II interface.=20 Since there were no terminations for LVTTL, I suspect it can give more noise compared to=20 SSTL. Comments are appreciated. Even between SSTL2-I and II the power:signal is nearly same (the quite node noise is similar),=20 with class-II is slightly more than class-I and in lower power:signal ratios, the noise is less in=20 class-II compared to class-I.=20 I feel SSTL2-class-II have two terminations, which makes the interface less noisier compared to SSTL2-Class-I. Comments are appreciated. Regards Canes __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around=20 http://mail.yahoo.com=20 ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net List archives are viewable at: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu