Subject: V/I table in Bench measurements

From: [email-masked] (Syed Huq)
Date: Tue, 19 Jul 94 15:09:33 PDT

Hi fellow gurus:

	Got two questions about the V/I table. 

1) Does the Voltage table need to ramp down from a -ve number to a +ve or can it
   be from +ve to -ve number as well ?
   Ex: For [Pulldown] the Voltage table goes from -5.0V to +10.0V

2) For most of the V/I table, IBIS shows that the voltage range should go from
   +10V to -5V. Problem is, there are devices whose I/O structure cannot handle
   swings that large. In that case, since we should not test a device beyond
   it's Absolute Recommended Operating(ABS Max) range, is it O.K  NOT to swing
   the I/O all the way to +10 to -5V ???

Regards,
Syed huq
National Semiconductor

---

From: [email-masked] ( Bob Ross)
Date: Wed, 20 Jul 94 13:45:31 PDT

Syed:

Here are my views on your questions:

(1) The Voltage table can be presented in any order: -ve to +ve or +ve to -ve.
(2) The table itself must go to at least the specified limits.  It is 
permissible to do the measurements over a reasonable range and then extrapolate
to the end points.  For example, you man not want to measure below -2V, but you
still need to provide at least one extrapolated data point out to -5V if Vcc
is 5V.

Bob Ross,
Interconnectix, Inc.

---

From: Stephen Peters <[email-masked]>
Date: Wed, 20 Jul 1994 15:43:59 -0700

Hello Bob, Syed:

     You know, Syed's question brings up an interesting point.  Suppose the
     VCC of a device is at +5V but the output is TTL and the maximum swing
     is, say 3.5V.  Should the output be characterises from -3.5 to 7.0v
     (the maximum voltage range that the output would ever realistically see) 
     or does one still have to do the -5 to +10v range?

                  Best Regards,
                  Stephen Peters
                  Intel Corp.

Syed:

Bob Ross,
Interconnectix, Inc.

---

From: [email-masked] ( Bob Ross)
Date: Wed, 20 Jul 94 18:10:43 PDT

Stephen:

For compliance with all versions of IBIS, the tables need to extend (even
by extrapolation) to the full -5V to 10V range.  I agree, you will never
see the full range in practice.  Since open collector versions of TTL 
could swing from Vcc (say 5V) to nearly 0V, I would not want to complicate the
range specification at this point.  (I personally favor not forcing the
tables to be at the specified IBIS limits, but that is a separate issue
and not the IBIS position.)

With some simulators, there are some subtle behavior effects which could give
significantly different simulations for what appear to be negligible IBIS
differences.  If for TTL the [Pullup] table has an I = 0 point at say 3.5V 
(actual voltage, not table voltage), and a [Pulldown] I = 0 point at say .2V,
then the [Ramp] rise and fall transitions can extend over a 3.3V range with
some simulators.  However, if the [Pullup] table has a current of I = -1e-6
at 3.5V and I = 0 at 5V, then the [Ramp] rise and fall transitions can 
extend over a 4.8V range (some of which is in the 3.5V to 5V high Z region).
This can cause a long time-constant dribble up in the low to high transition
into a high resistance load.  It may also give a different effective ramp rate.
Related to this is the extraction of the dV/dt_f ramp rates with 50 ohms to
Vcc = 5V versus 50 ohms to say Vcc - 1.5 = 3.5V.  Some Spice simulations give
much slower ramp rates under the first condition than under the second, 
more realistic situaton which does not force a transition through the 
high impedance region.  So, with TTL there can be some practical considerations
which do not apply for CMOS Logic.  Along with the range question you raise,
IBIS does not address these concerns.

Bob Ross,
Interconnectix, Inc.

---

From: [email-masked] (Syed Huq)
Date: Fri, 22 Jul 94 12:42:48 PDT

Hello:
	I think bench data should be taken without exceeding the ABS MAX rating
	of the device. This could mean a swing smaller than the specified
	-5V to +10V. Maybe, the simulator can extrapolate the data point to the 
	desired level. I am not sure if all simulators can do that or not.

Regards,
Syed Huq
National Semiconductor

> From [email-masked] Wed Jul 20 16:15:25 1994
> To: [email-masked], [email-masked]
> Subject: Re[1]:  V/I table in Bench measurements
> Date: Wed, 20 Jul 1994 15:43:59 -0700
> From: Stephen Peters <[email-masked]>
> Content-Length: 1624
> 
> 
> Hello Bob, Syed:
>

---

From: Will Hobbs <[email-masked]>
Date: Fri, 22 Jul 94 13:26:01 PST

Text item: 

Syed,

I agree that you should not try to sweep beyond what you think the part can 
safely handle.  I suggest you do the extraploation, however, as that will give 
you the control over what the customers see.  Consceivably a simulator might not
extrapolate in the way you would want, or not do so at all.

Will Hobbs
Intel Corp.

Hello:

Regards,
Syed Huq
National Semiconductor

> >    the I/O all the way to +10 to -5V ??? 

Text item: External Message Header

The following mail header is for administrative use
and may be ignored unless there are problems.

***IF THERE ARE PROBLEMS SAVE THESE HEADERS***.

Cc: [email-masked]
Subject: Re: Re[1]:  V/I table in Bench measurements
To: [email-masked], [email-masked], [email-masked]
From: [email-masked] (Syed Huq)
Date: Fri, 22 Jul 94 12:42:48 PDT

---

From: Arpad Muranyi <[email-masked]>
Date: Mon, 25 Jul 94 09:39:21 PST

Steven, Syed,

Now that I am back from my vacation, here is my opinion on these questions:

The reason we require these "extreme" ranges in the models is to make sure that 
all simulators handle the curves as they should in such extreme situations.  If 
you can not measure that far, make an intelligent extrapolation to extend the 
data to the required range.

Regarding the TTL device in a 5V environment, in my opinion, it should still use
-5V to +10V, because there might be another device in the system that is CMOS, 
and very well overshoot beyond 7V.

I feel that the ordering of the voltage should go from -V to +V and not +V to 
-V, because SPICE can not handle decreasing voltage tables in their PWL sources.
For those who are using IBIS models on SPICE platforms this is important.

Arpad Muranyi
Intel Corporation

Hello Bob, Syed:

     (the maximum voltage range that the output would ever realistically
see)

                  Best Regards,
                  Stephen Peters
                  Intel Corp.

Hi fellow gurus:

1) Does the Voltage table need to ramp down from a -ve number to
a +ve or can it
   be from +ve to -ve number as well ?
   Ex: For [Pulldown] the Voltage table goes from -5.0V to +10.0V

2) For most of the V/I table, IBIS shows that the voltage range should
go from
   +10V to -5V. Problem is, there are devices whose I/O structure
cannot handle
   swings that large. In that case, since we should not test a device beyond
   it's Absolute Recommended Operating(ABS Max) range, is it O.K
 NOT to swing
   the I/O all the way to +10 to -5V ???

Regards,
Syed huq
National Semiconductor