Subject: Transit time extraction related issues for IBIS 3.0

From: "A. D. Shirpadaraj" <[email-masked]>
Date: Wed, 25 Mar 1998 13:10:44 +0531 (IST)

Hi,

Can anybody explain me  the importance of Transit time information(with 
reference to IBIS 3.0 spec).

I simulated an I/O buffer spice netlist(disabling the output so that I
can get only clamp data), attaching the load(as specified in the section
"Notes on Data derivation method" of IBIS 3.0 spec doc) and connecting
a pulse generator with falling edge rate of 1ns.

Input of I/O buffer is at Gnd level.

   _________                                            _______
  |         |         ______________                   |PULSE  |
  |I/O BUFF |--0-----|______________|-------\/\/\/\----|GEN    | __ 
  |         |  ^         T LINE               10 OHM   |_______|   \
   ---------   |                                                    \
               |                                                     \______
               |____ tdrv

The simulation result is as follows,          

       time    voltage      voltage    
             (Pulse gen)      tdrv    
   0.            3.3000       3.3000   
 400.00000p      1.9800       3.3000   
 800.00000p    660.0000m      3.3000   
   1.20000n      0.           2.7999   
   1.60000n      0.           1.1855   
   2.00000n      0.        -745.8083m  
   2.40000n      0.        -765.5829m  
   2.80000n      0.        -764.9445m  
   3.20000n      0.        -766.0098m  
   3.60000n      0.        -743.5182m  
   4.00000n      0.        -593.9329m  
   4.40000n      0.        -480.4755m  
   4.80000n      0.        -451.3177m  
   5.20000n      0.        -454.4898m  
   5.60000n      0.        -286.7090m  
   6.00000n      0.         152.1383m  
   6.40000n      0.         292.0734m  
   6.80000n      0.         307.6836m  
   7.20000n      0.         300.9822m  
   7.60000n      0.         323.2456m  
   8.00000n      0.         243.2512m  
   8.40000n      0.         -10.6594m  
   8.80000n      0.        -152.1871m  
   9.20000n      0.        -193.6911m  
   9.60000n      0.        -196.4707m  
  10.00000n      0.        -222.0614m  
  10.40000n      0.        -164.7043m  
  10.80000n      0.         -24.4593m  
  11.20000n      0.          78.7876m  
  11.60000n      0.         115.6422m  
  12.00000n      0.         125.1014m  
  12.40000n      0.         145.4857m  
  12.80000n      0.         119.0935m  
  13.20000n      0.          35.9285m  
  13.60000n      0.         -34.7450m  
  14.00000n      0.         -69.3589m  
  14.40000n      0.         -80.1839m  
  14.80000n      0.         -96.5231m  
  15.00000n      0.        -100.8460m 

 The driver output is having both positive and negative glitches.

 How to find transit time (TT) from this data.

What extra information does the TT keyword conveys to a
signal integrity analyser? Whether all buffers have some finite amount
of TT or only some with strong clamp.

Thanks

A.D. Shripadaraj

Cadence Design Systems
NOIDA, INDIA

[email-masked]