RE: [IBIS] termination on input buffer

From: Chee Pin Chan <cpchan_at_.....>
Date: Sun May 17 2009 - 19:24:34 PDT
Dear Babid A,

Regarding your enquiry on the input termination in the IBIS file, I would like to shed you some light on the input on chip termination information if it is embedded into the clamps of the IBIS model. Take the differential LVDS input with 100ohm on chip termination as example; you would be able to see in the ground clamp curve that there is a nearly linear region normally around the VCM. Assuming the curve is linear (with resistive load), and by performing normal R = dV/dI at the linear region (usually near Vcm), you would be able to get the R ~ 100 ohm. For the differential LVDS input without on chip termination, by performing the same steps, you would be getting the R in kOhm or MOhm which is the expected high impedance..

Examples:

1) LVDS input without OCT (gnd clamp)

9.8485e-01          -1.3747e-04   -8.6054e-05   -1.7763e-04
1.0606e+00          -9.8227e-05   -4.8802e-05   -1.3748e-04
1.1364e+00          -5.8938e-05   -1.1577e-05   -9.7341e-05
1.2121e+00          -1.9651e-05   2.5600e-05    -5.7176e-05
1.2879e+00          1.9611e-05    6.2702e-05    -1.7014e-05
1.3636e+00          5.8831e-05    9.9719e-05    2.3136e-05
1.4394e+00          9.7995e-05    1.3670e-04    6.3269e-05
1.5152e+00          1.3708e-04    1.7357e-04    1.0332e-04
1.5909e+00          1.7607e-04    2.1044e-04    1.4338e-04
1.6667e+00          2.1499e-04    2.4719e-04    1.8344e-04

R ~ (9.8485e-01 - 1.66670)/(-1.3747e-04 - 2.1499e-04) = 1.93kOhm

2) LVDS input with 100Ohm OCT (gnd clamp)

1.1364e+00          -1.1973e-03   -2.1547e-04   -2.0607e-03
1.2121e+00          -3.9894e-04   4.7429e-04    -1.2113e-03
1.2879e+00          3.9841e-04    1.1609e-03    -3.6063e-04
1.3636e+00          1.1933e-03    1.8447e-03    4.8961e-04
1.4394e+00          1.9837e-03    2.5246e-03    1.3382e-03
1.5152e+00          2.7695e-03    3.2008e-03    2.1837e-03

R~ (1.1364 - 1.5152)/(-1.1973e-03 - 2.7695e-03) = 95 Ohm

Please feel free to let me know if you have any concern. Thank you.

Best Regards,
Chan, Chee Pin
Component Applications Engineer
Altera Corporation


________________________________
From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Babid A
Sent: Sunday, May 17, 2009 4:42 AM
To: ibis-users@eda.org; ibis@eda.org
Subject: [IBIS] termination on input buffer

Hi,

How to determine if the input is terminated from a IBIS file? What is the keyword that I should look for?

-Thanks,



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Received on Sun May 17 19:26:37 2009

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