FreeLists / si-list / [SI-LIST] don't lump that C (new subject)

["Peterson, James F \(EHCOE\)" <james.f.peterson@xxxxxxxxxxxxx>]

Note to Si-listers : Canes and I have been exchanging off-list email
regarding this subject. Even though this is very familiar to some on the
list, I thought I'd copy you all since it's still a common
misconception. -jim
 

________________________________

From: Peterson, James F (EHCOE) 
Sent: Wednesday, May 02, 2007 8:04 AM
To: 'Canes Venatici'
Subject: RE: [SI-LIST] SSO SSTL Vs LVTTL

 

Canes,

 

That's the beautiful and remarkable thing about lossless transmission
lines. They do not distort, they only delay.  The reason they don't
distort is because the t-line looks resistive, not capacitive or
inductive.  And, indeed, this is what the edge of your signal sees (not
the steady state portion of your signal).

 

For a couple references see page 143, last paragraph, of Dr. Johnson's
book "High Speed Digital Design - Black Magic" and the last 2 paragraphs
on page 295 of  Ron Poon's "Computer Circuits Electrical Design".

 

If you have a 10 inch t-line at 4pf per inch, you can't add up the C per
inch and replace it with a 40pf cap because "the capacitive effect is
tuned out by the inductive effect, and the ladder network just acts as
an ideal delay line : it does not degrade the signal risetime and
falltime" (R. Poon).

 

Jim Peterson

 

________________________________

From: Canes Venatici [mailto:starsilic@xxxxxxxxx] 
Sent: Wednesday, May 02, 2007 3:03 AM
To: Peterson, James F (EHCOE)
Subject: Re: [SI-LIST] SSO SSTL Vs LVTTL

 

Jim,
Could you tell me why, for the drivers the T-lines are seen as resistive
load?
Why I'm asking is during transients only SSN occurs. During that time,
the
drivers see the T.Lines as inductors and capacitors/unit length, is my
understanding.
Probably during steady state they (T.Lines) can be seen as resistive
loads.
Could you correct/explain me if I'm wrong?

Regards
Canes.

----- Original Message ----
From: "Peterson, James F (EHCOE)" <james.f.peterson@xxxxxxxxxxxxx>
To: starsilic@xxxxxxxxx
Sent: Tuesday, May 1, 2007 1:05:55 AM
Subject: RE: [SI-LIST] SSO SSTL Vs LVTTL

From what I have seen, and it's mostly been the results from simulators
and what I've read, so I don't have a lot of lab data to back this up,
using this approach of approximating the SSO current with the source
impedance is pretty accurate...that said, you do have to figure out what
the source-Z is, but there are a couple excellent ways to do that.

 

 Your second paragraph below is not clear to me. I'm not sure I
understand the question, but remember that to a driver, t-lines look
resistive, not capacitive or inductive. You can't lump together the C
and L.

 

-Jim

 

________________________________

From: Canes Venatici [mailto:starsilic@xxxxxxxxx] 
Sent: Monday, April 30, 2007 9:13 AM
To: Peterson, James F (EHCOE)
Cc: si-list@xxxxxxxxxxxxx
Subject: Re: [SI-LIST] SSO SSTL Vs LVTTL

 

Jim Peterson,
Thanks for your reply. The only concern is the impedance of the driver
may be non-linear,
depending upon the state (cut-off/linear/saturation) of the transistors,
so I was wondering
can we approximate the driver impedance.

Also I've one more doubt regarding the simulations using T.Lines. I used
4inch lossless transmission line.
The equivalent i/p inductance comes around 33nH and capacitance comes to
be 13pF, by simple formulas
of T.lines. With this if I do simulations, I get very high power cell
requirement for each signal cell, or the quite node
noise is very high.

I could see in some docs related to SSO simulations, they were just
putting series resistor at the output of the driver, followed by
termination resistor pulled to Vtt for SSTL interfaces, instead of
T.lines in their SSO set-ups. 
Could anyone clarify on how well it can represent SSO noise simulations?

Regards
Canes

----- Original Message ----
From: " Peterson, James F (EHCOE)" <james.f.peterson@xxxxxxxxxxxxx>
To: si-list@xxxxxxxxxxxxx
Cc: starsilic@xxxxxxxxx
Sent: Monday, April 30, 2007 5:07:14 PM
Subject: RE: [SI-LIST] SSO SSTL Vs LVTTL

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. 

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 
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. 
Since there were no terminations for LVTTL, I suspect it can give more
noise compared to 
SSTL. Comments are appreciated.

Even between SSTL2-I and II the power:signal is nearly same (the quite
node noise is similar), 
with class-II is slightly more than class-I and in lower power:signal
ratios, the noise is less in 
class-II compared to class-I. 
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 
http://mail.yahoo.com 

------------------------------------------------------------------
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:
http://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:     
        http://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
  

 

 

________________________________

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.
<http://us.rd.yahoo.com/evt=48245/*http:/autos.yahoo.com/new_cars.html;_
ylc=X3oDMTE1YW1jcXJ2BF9TAzk3MTA3MDc2BHNlYwNtYWlsdGFncwRzbGsDbmV3LWNhcnM-
>  

 

 

________________________________

Ahhh...imagining that irresistible "new car" smell?
Check out new cars at Yahoo! Autos.
<http://us.rd.yahoo.com/evt=48245/*http:/autos.yahoo.com/new_cars.html;_
ylc=X3oDMTE1YW1jcXJ2BF9TAzk3MTA3MDc2BHNlYwNtYWlsdGFncwRzbGsDbmV3LWNhcnM-
>  


------------------------------------------------------------------
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:
http://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:     
                http://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