Mey-Yee, True, the waveforms in the waveform tables of an IBIS model do include the buffer's internal capacitance effects, and if we just added a C_comp capacitor to the buffer model's output we would double count for those effects. However, most simulators I know have a special compensation algorithm to prevent this from happening because the capacitor has to be there, because the model's current source doesn't behave as a capacitor and when reflected waves arrive at the buffer, it will not look capacitive and the reflection coefficients from the buffer will be incorrect. I like to summarize this the following way: The C_comp capacitor has to be made visible when you look into the buffer from the outside, but invisible to the internals of the buffer model. Arpad ======================================================= ________________________________ From: NG,MEI-YEE [mailto:mei-yee.ng@avagotech.com] Sent: Sunday, September 28, 2008 7:05 PM To: Muranyi, Arpad; ibis@server.eda.org Cc: ibis-users@server.eda.org Subject: RE: [IBIS-Users] RE: [IBIS] C_comp value Hi Arpad, Just one quick question, if the netlist I used for the pad is an extracted netlist, does that mean the C_comp value is already incorporated inside (parasitics and all)? In that case, if I still put in an additional C_comp value, it would mean that I'm double-counting the C_comp? Thank you. Best regards, Mei Yee MCPD, Avago Technologies (Malaysia) Tel no.: +604-6108515 ________________________________ From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Muranyi, Arpad Sent: Friday, September 26, 2008 9:03 PM To: ibis@server.eda.org Cc: ibis-users@server.eda.org Subject: [IBIS-Users] RE: [IBIS] C_comp value Timmy, You can do it either way, it depends on your needs. If you want to correlate to your SPICE model, match it to that, if you want to correlate to real life, match it to your measurements. Arpad ==================================================== ________________________________ From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On Behalf Of Timmy Leon Sent: Thursday, September 25, 2008 8:46 PM To: ibis@server.eda.org Cc: ibis-users@server.eda.org Subject: [IBIS] C_comp value Dear Sir/Madam, I have a question regarding the c_comp value that we should put in IBIS model. Should the c_comp value be based on measurement, or can we tune value so that IBIS model correlate with its spice model or measurements? Thank you. Best regards, Timmy Leon -- This message has been scanned for viruses and dangerous content by MailScanner <http://www.mailscanner.info/> , and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner <http://www.mailscanner.info/> , and is believed to be clean. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. -------------------------------------------------------------------- |For help or to subscribe/unsubscribe, e-mail majordomo@eda-stds.org |with the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or e-mail a request to ibis-request@eda-stds.org. | |IBIS reflector archives exist under: | | http://www.eda-stds.org/pub/ibis/email_archive/ Recent | http://www.eda-stds.org/pub/ibis/users_archive/ Recent | http://www.eda-stds.org/pub/ibis/email/ E-mail since 1993Received on Sun Sep 28 21:22:21 2008
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