Subject: BIRD 7 Comment on ECL

From: [email-masked] ( Bob Ross)
Date: Mon, 24 Jan 94 13:48:58 PST

Hello IBIS team:

After thinking about Kumar's question to Arpad Muranyi's and Stephen Peter's
recent ECL addition on ramp rates to Kellee Crisafulli's added notes, I want 
to list how we can identify ECL model types and its variations (e.g. ECL 
tied to a positive supply as in PECL) based on IBIS Version 1.1 and approved
BIRDS 3 and 4:

The IBIS Model is "ECL-type" if the pullup and pulldown "typical" reference
voltage values are the same. These values can be extracted from the model
and compared for equality.  Such an extraction would be based on the 
[Voltage range], [Pullup reference] and [Pulldown reference] typical_values 
and on which take precedence over the other.

Also, the equality can be tested based on satisfying one of the cases:

(1) [Pullup reference] typ_val = [Pulldown reference] typ_val
        | e.g. 5.V = 5.V regardless of [Voltage range] typ_val or
        | whether [Voltage range] keyword is not present

(2) [Voltage range] typ_val = [Pulldown reference] typ_val
     AND [Pullup reference] keyword not present

(3) [Voltage range] typ_val = [Pullup reference] typ_val = 0
    AND [Pulldown reference] keyword not present (default is 0V)

(4) [Voltage range] typ_val = 0
    AND [Pullup reference] and [Pulldown reference] keywords not present
    (default for pulldown reference is 0V)

I am not sure if an IBIS model can be considered ECL if the pullup or
pulldown data spans exactly a range from Vcc to Vcc - 2.2 because I do
not know whether "spanning the range" means that the data cannot exceed
this range.  (E.g., I may be able to get a good data point at Vcc - 2.3V.)

If "ECL-type" then [Pulldown] data follows Vtable = Vout - Vcc order.

It might be easier to consider Model_types "Output_ECL" and "I/O_ECL"
(and for completeness "Input_ECL" although "Input" works the same with ECL).  
BIRD 1 (which was replaced by BIRDS 3 and 4) originally proposed Model_type
"ECL".  

The real issue is how explicit should IBIS be in specifying the Model_type,
especially when such knowledge is critical in knowing how to interpret the
[Model] data.  A robust set of Model_type information can simplify the mapping
of the IBIS data into internal data structures which do not have to carry
the same level of distinctions.  The internal data structures can rely as
appropriate on other relationships and still have the same functionality. 

Bob Ross
Interconnectix, Inc.