Open drain models are not tricky at all. The output hi voltage is dependent on three things. Vdd, Rload and the off current of the open drain driver. Vdd is normally the power supply voltage. The resistor used in IBIS modeling is usually 50 Ohms and the current in an off FET is usually 0.00mA. So the off voltage is usually Vdd. Vout = Vdd - Ioff*50Ohms = Vdd - 0 = Vdd If you are getting a different value you are mostly likely not having the proper Vdd value, the off current is not zero or you have other currents in your model that are being summed with the FET's current in such a way that there is current flowing in the load causing an IR drop. I would check the power and ground clamp tables to see if they are contributing any current to the output. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 tom@teraspeed.com www.teraspeed.com Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 401-284-1827 -----Original Message----- From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Amit KUMAR Sent: Friday, September 21, 2007 6:19 AM To: ibis-users@server.eda.org Cc: amit kumar Subject: [IBIS-Users] Problem in developin NMOS Open Drain type IBIS Hello all, I am generating IBIS model(ver 4.2) for a circuit which is working in Open drain mode. I have included in the IBIS file one pulldown curve and 2 V-T waveforms (both with high fixture, one falling and one rising). Simulations show that the operating point for high input is different in case of original circuit and IBIS file. For low input it is the same. So when i give some Falling input at the input of model both the IBIS waveform and original waveform fall to the same voltage but at the start they are at different voltage. Infact i get operating point for high input half of the voltage which i should actually get.. Is their something tricky in modelling of Open Drain model ?? I have modelled a few IBIS models of output type and I/O type but never did i get such a problem. Thanks for your support Amit Kumar Design Engineer ST Microelectronics India -- 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 1993 -- 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 Fri Sep 21 10:34:30 2007
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