BIRD 7 (more from Kellee Crisafulli)

From: Kellee Crisafulli, HyperLynx

To: Bob Ross, Bob Ward and fellow IBISers

Re: BIRD 7, Resending, (1/2 of the document was lost in the mail)

For some reason only 1/2 of my Email was transmitted. I recreated the
the 2nd 1/2 from memory and am resending it.

Also, at the end of this document is my response to Bob's last message.

My apologies, I don't know where the other 1/2 landed ...
(perhaps in the IBIS bird bath)

Bob, I basically like what you have proposed in BIRD 7 for the additional
key words. I have been going to send in a bird on this, but have been
waiting for the results of an in-house project we are doing to develop some
ABT models under IBIS. We have nearly completed this project and I can
report on this now.

I also have a few concerns with bird 7, specifically:
  1) I believe we absolutely must address the dv/dt issue for the turn off
     side. We could do this by simplystating explicitly in the
     specification that the dv/dt associated with opposite side is used as
     the turn-off time of the open-side device. However it must include a
     load specification during turn off. and specify this being valid for
     the a load resistor to the opposite rail.

  2) I think it would be very useful to most semi-conductor companies
     developing models to require that V/I table data match the model type
     exactly. This way the IBIS parse can check it and help find errors in
     manually entered data.

  3) If I am not mistaken CMOS has an open_drain p channel and an open_drain
     N channel device there is no open_source configuration that I know of
     unless you consider some of the 3 volt outputs with totem pole type
     N-channel outputs. Therefore the key word open_source may not be
     appropriate. I propose instead that we use just Open_drain to indicate
     either an N channel/P channel, open collector, or open emitter type
     output. The thing that differentiates them is simply the missing V/I
     data for the output.

HyperLynx now has IBIS simulations running of ABT buffers (FutureBus) which
look pretty good. These require the open_drain model type and have an
additional offset for the output diode. I therefore feel good about
recommending the use of IBIS for modeling open side devices.

I beleive we should modify BIRD7 as follows:
*********************************************

1) Modify the "Usage Rules" under the Keyword Model, to show Open_drain
   instead of Open-drain. (exactly as Bob suggested)

2) Add only one new keyword "I/O_open_drain" to the list in usage rules,
   and the Model_type line. This keyword allong with Open_drain can
   represent all open side devices. The absence of either the Pullup and
   Pulldown V/I table can be used to indicate which side is open.

3) Change the section titled NOTES ON DATA DERIVATION METHOD as follows:

  Section 3 on Ramp rates:
  ------------------------
  3) Ramp Rates:
     The ramp rates (listed in AC characteristics below) should be derived
     as follows:
       1)Start with the silicon model, remove all packaging.

       2)If: The model type is one of the following: Output, I/O, or 3-state
         Then: Attach a 50 ohm resistor to GND to derive the rising edge
               ramp.
               Attach a 50 ohm resistor to POWER to derive the falling
               edge ramp.

         If: The model type is either (Open_drain or I/O_open_drain) and
             the Pullup V/I table is missing.
         Then: Attach either a 50 ohm resistor or the vendor suggested
               termination resistance to either POWER or the vendor suggested
               termination voltage. Use this load to derive both the rising
               and falling edges.

         If: The model type is either (Open_drain or I/O_open_drain) and
             the Pulldown V/I table is missing.
         Then: Attach either a 50 ohm resistor or the vendor suggested
               termination resistance to either GND or the vendor suggested
               termination voltage. Use this load to derive both the rising
               and falling edges.

        4-6) renumber these 3-5

        7) **** Delete item 7 ******

4) Under the Pullup, Pulldown keyword section in usage rules, add the
   following:

        If the model type is (Output, I/O, or 3-state) then both the Pullup
        and Pulldown V/I tables are required.

        If the model type is either (Open_drain or I/O_open_drain) then
        only one "Pull" V/I table (Pullup or Pulldown) may be present.

        
Postmortum:
-----------
After reading Bobs response to 1/2 of my Email I agree that the usage
of open_source is being used by some vendors in a somewhat confusing manor.
i.e. they call the open drain P channel devices open_source. While I think
this is an inconsistant usage, I am willing to use Open_source and
I/O_open_source as Bob suggested if the entire IBIS group strongly perfers
this.

I DO NOT however want to choose a solution that deletes the existing
Open_drain model type as this is not backward compatible with the
specification.

Note: 3_state_open_drain is a redundant definition and is therefore not
needed. (i.e. open_drain by definition is 3-stated if it is off)

Summary:
--------
Using just two key words, Open_drain, and I/O_open_drain is simple, and
maintains backward compatibility, and covers all the cases so far...

P.S. thankyou for the Fax, Bob.

Best wishes to all...... Kellee


Received on Fri Jan 21 00:14:45 1994