Date: Tue Mar 26 2013 - 07:57:11 PDT
Rinsha, That drawing doesn't show the input terminal for the buffer, because it assumes that it has enough separation for not having any capacitance currents flow that way, but for debugging your case it would be useful to put a current measurement there too to see if your summation is not working because of that. If you can't get all the terminal currents to add up to zero you must have something inside the buffer which creates or loses energy. This could be in the form of an ideal source, a connection to the infamous global ground node in SPICE (node zero), or similar. By the laws of electronics/physics the all currents in/out of a box has to sum up to zero. I hope this helps, Arpad ========================================================== From: Rinsha Reghunath [mailto:Rinsha.Raghunath@synopsys.com] Sent: Tuesday, March 26, 2013 4:55 AM To: Muranyi, Arpad; ibis@eda.org; ibis-users@eda.org Subject: RE: C_comp subparameters extraction Hi Arpad, I have used the same setup for measuring both C_comp and its subparameters as per the following method specified in the cookbook, where it is mentioned that "The circuit for measuring split C_comp values is very similar to that used for the basic C_comp simulation, except the current will be measured at the supply connections, instead of the I/O pad." In the buffer which I am modeling, there is only one Vcc and one GND terminal, and the currents are measured through these. But the resulting C_comp subparameter values calculated based on these measured currents doesnot add up to the original C_comp. [cid:image001.jpg@01CE2A08.00D50AF0] Thanks, Rinsha From: owner-ibis@eda.org<mailto:owner-ibis@eda.org> [mailto:owner-ibis@eda.org] On Behalf Of Muranyi, Arpad Sent: Tuesday, March 26, 2013 1:54 AM To: ibis@eda.org<mailto:ibis@eda.org>; ibis-users@eda.org<mailto:ibis-users@eda.org> Subject: [IBIS] RE: C_comp subparameters extraction One more thing I forgot to mention: How many power and ground terminals does your buffer have? If there is more than just one Vcc and one GND terminal, are you sure you are measuring all the possible paths the current might take (including the input terminal)? This might be an "obvious" point, but are you sure that there are no internal sources in your buffer model providing power to any part of the buffer? I hope this helps too... Thanks, Arpad =========================================================== From: owner-ibis@eda.org<mailto:owner-ibis@eda.org> [mailto:owner-ibis@eda.org] On Behalf Of Muranyi, Arpad Sent: Monday, March 25, 2013 3:18 PM To: ibis@eda.org<mailto:ibis@eda.org>; ibis-users@eda.org<mailto:ibis-users@eda.org> Subject: [IBIS] RE: C_comp subparameters extraction Rinsha, Are you making sure that the conditions between your measurements are the same? C_comp is a tricky thing. It can vary with lots of things. For example, the C_comp you measure could be different when the buffer is 3-stated, diving high or driving low. It also varies with bias voltage, i.e. with the voltage at the pad of the buffer. In order for the numbers to "add up" you have to make sure that you add them up when they are under the same conditions. I hope this helps, Arpad From: owner-ibis@eda.org<mailto:owner-ibis@eda.org> [mailto:owner-ibis@eda.org] On Behalf Of Rinsha Reghunath Sent: Monday, March 25, 2013 5:41 AM To: ibis@eda.org<mailto:ibis@eda.org>; ibis-users@eda.org<mailto:ibis-users@eda.org> Subject: [IBIS] C_comp subparameters extraction Hello, I was trying out the extraction of C-comp subparameters, namely, C_comp_pullup, C_comp_pulldown, C_comp_power_clamp, and C_comp_gnd_clamp according to the methodology specified in IBIS cookbook version 4.0, section 3.3.1. But the extracted C_comp subparameter values doesnot sum up to the actual C_comp value extracted. How is the Miller cap being taken care of in this case? Is there any documentation on the same? Thanks & Regards, Rinsha -- 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<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 mikelabonte@eda-stds.org |or ibis-request@eda-stds.org | |IBIS reflector archives exist under: | | http://www.eda-stds.org/ibis/email_archive/ Recent | http://www.eda-stds.org/ibis/users_archive/ Recent | http://www.eda-stds.org/ibis/email/ E-mail since 1993
