From: ARiazi (ARIAZI@prodigy.net)
Date: Sat May 13 2000 - 09:35:24 PDT
This communication focuses on topic of model evaluation by presenting:
1. A comparison of parasitics for SSOP and TSSOP packages of an IC model (Philips 74ALVCH16245 which is a 16-bit bus transceiver).
2. An appraisal of IV characteristics of the same device using the Visual IBIS Editor.
Such model analyses, although simple, can provide valuable data and prove rewarding.
Illustrated below are parasitic parameters belonging to two different packages of an IC IBIS models.
Philips Semiconductor, Inc. 74ALVCH16245, Package: SSOP48
| variable typ min max
R_pkg 66.00mO 46.90mO 85.10mO
L_pkg 4.4500nH 2.1700nH 6.7300nH
C_pkg 0.907pF 0.512pF 1.302pF
Philips semiconductors Inc., 74ALVCH16245, Package: TSSOP48
| variable typ min max
R_pkg 69.35mO 46.8mO 91.9mO
L_pkg 5.31nH 3.33nH 7.29nH
C_pkg 0.728pF 0.443pF 1.013pF
Above values indicate that R_pkg and L_pkg for SSOP package are less than those for TSSOP , whereas C_pkg for SSOP exceed C_pkg for TSSOP package. More important, studying parasitics reveal the expected value range for various packages which is useful. when creating or validating a model..
Another recommended examination, to gain critical information about model quality, is to view the IV or VT curves by means of the Visual IBIS Editor (freely available from Hyperlynx). For example, the attached gif file, illustrates the pull down curve for Philips 74ALVCH16245. It indicates that for the typical corner, the current value at 3.0V exceeds 100mA. This appears inconsistent with the value given in the data sheet of the device which specifies IOL (Low Level Output Current) of 24 mA at Vcc = 3.0 V.
In closing, comparing or analyzing the parasitic parameters for various packages, provides valuable insight towards accurately creating or validating behavioral models. The visual IBIS Editor, freely obtainable from Hyperlynx, aids rapid examination of the IV and VT curves of a model and appraisal of its quality. Here, by an example, a discrepancy was pointed out between the IV data of a model and the value specified in the device's data sheet. In the past, I have also utilized the Visual IBIS editor to compare or correlate the IV curves of one manufacture's model with an equivalent model by another manufacturer (for instance the pulldown curves of Philips 74ALVCH16245 and Ti 74ALVCH16245 IBIS models), and to draw conclusions regarding the expected performance of these models in a SI simulation.
Genuinely appreciating your comments and with warm wishes,
2251 Lawson Lane
Santa Clara, CA 95054
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