RE: [IBIS-Users] Extract IBIS data from lab measurement

Yuanchen,

I would suggest that you measure your clamp I-V curves

with a sweep that starts from 0 V going in the negative

direction or from Vcc going in the positive direction.

This way you don't begin the sweep and blow the chip at

the beginning of the sweep.

I would also suggest that you use a curve tracer which

can get the measurement done in one sweep (as opposed to

repetitive sweep to get multiple points) because that

way the chip doesn't heat up so much, and you can sweep

out to any voltage (if you can allow yourself to blow

the chip while you do this), but you will still get good

data until the chip blew up.

The other thin g you have to keep in mind is that you

need a power supply that can sink and source the current.

Most supplies can only do one, which means that they

regulate against the load pulling the voltage between GND

and Vcc together, but they don't regulate against the

load pushing the voltage apart (in other words pushing

Vcc up from GND). When you measure the clamping diodes

on the Vcc side, you are actually pulling the Vcc voltage

up with the curve tracer, and if your supply can't hold

Vcc down, the Vcc voltage will "float" upward while you

do your sweep. This will come across as a much weaker

diode current reading in your measurement...

Arpad

===========================================================

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of Tom Dagostino
Sent: Tuesday, November 23, 2010 3:41 AM
To: 'ji xiao'; 'ibis-users'
Subject: RE: [IBIS-Users] Extract IBIS data from lab measurement

Yuancheng

It is easy to extract good VT data from a measurement if you have the
proper equipment. We've done this for 1000s of models.

Hopefully you are not trying to measure at -3.3V. If you are I can
understand that there would be a large difference between what is
measured and what the manufacture's model shows. I've not seen an IC's
ground clamp that could handle that much forward bias. You need to keep
the forward bias to a volt or less in most cases and extrapolate to
-Vdd. But without knowing what difference you are seeing it is hard to
tell why you are seeing it.

Regards,

Tom Dagostino

Teraspeed Labs

13610 SW Harness Lane

Beaverton, OR 97008

503-430-1065

tom@teraspeed.com

www.teraspeed.com

Teraspeed Consulting Group LLC

121 North River Drive
Narragansett, RI 02882

401-284-1827

www.teraspeed.com

From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On
Behalf Of ji xiao
Sent: Tuesday, November 23, 2010 1:15 AM
To: ibis-users
Subject: [IBIS-Users] Extract IBIS data from lab measurement

Dear all,

I want to extract the IV and Vt data from the chip measurement results,
but there are two problems.

1. For the Vt data, IBIS cookbook Version 4.0 and 5.0 only mention the
procedure of extract ramp rate. If I want to extract the detail Vt curve
table from the measurement results of a packaged chip, is it possible?

2. For the IV data, I successfully extract it from the measurement but
the extracted result only show agreement with original IBIS model
(provided by manufacturer) for operation region. When out of the
operation region, i.e., in diode model, the IV characteristics I got is
quite different from the original one.

For example, the voltage operation region of my chip is [-0.5, 3.8], in
this range, the measurement value of current is reasonable. However, for
the current measured beyond this voltage range, such as [-3.3, -0.5],
the measurement result will distort severely from the original IBIS
value. Could anyone help me analyze the possible reason for the
disagreement? Or is there something wrong I may make in measurement
setting? (I made the measurement setup according to cookbook version4.0)

Thanks and regards,

Yuancheng

-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is
believed to be clean. 
-- 
This message has been scanned for viruses and 
dangerous content by MailScanner <http://www.mailscanner.info/> , and is
believed to be clean. 
-- 
This message has been scanned for viruses and
dangerous content by MailScanner, and is
believed to be clean.
--------------------------------------------------------------------
|For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org
|with the appropriate command message(s) in the body:
|
|  help
|  subscribe   ibis       <optional e-mail address, if different>
|  subscribe   ibis-users <optional e-mail address, if different>
|  unsubscribe ibis       <optional e-mail address, if different>
|  unsubscribe ibis-users <optional e-mail address, if different>
|
|or e-mail a request to ibis-request@eda-stds.org.
|
|IBIS reflector archives exist under:
|
|  http://www.eda-stds.org/pub/ibis/email_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/users_archive/ Recent
|  http://www.eda-stds.org/pub/ibis/email/         E-mail since 1993