Todd, Isn't your response on the IBIS-users reflector a prime example for what Bob was talking about in our IBIS-ATM meeting yesterday (that people will immediately be unhappy with the limited IBIS-SPICE subset we are proposing)? Arpad ======================================================== ________________________________ From: owner-ibis-users@xxxxxxxxxxxxxx [mailto:owner-ibis-users@xxxxxxxxxxxxxx] On Behalf Of Todd Westerhoff Sent: Thursday, August 28, 2008 7:37 AM To: Muniswara Reddy Vorugu Cc: Prabhat Ranjan; ibis-users@xxxxxxxxxxxxxx Subject: Re: [IBIS-Users] Dynamic behaviour of buffer Muniswara, The other possible solution the obvious one - use a SPICE model for the buffer - which could be either a transistor model or a behavioral structural model using controlled sources. The issue here is one of portability; there are a number of EDA/SI tools that use SPICE (or HSPICE) as their simulation engine, and could therefore make use of such a model. VHDL-AMS is certainly capable of modeling this behavior, but there are far fewer tools that would be able to run the model. If you're a semiconductor vendor producing a model for end-users, that's usually a consideration - you want a model that will run in as many tools as possible. Wouldn't it be nice if we could run SPICE models as easily as we use IBIS models? It's really not that hard. You simply need a traditional IBIS buffer model that also points to a corresponding SPICE model. The traditional IBIS buffer model only represents a single case of output loading, as you pointed out. The SPICE model works in any loading condition. If a particular EDA tool can't use the SPICE model directly, it still has a conventional IBIS buffer model based on the specific loading condition. If the EDA tool is able to use the SPICE model, then the user gets both the increased precision of the SPICE model and the benefit of the IBIS use model (graphically place the device in the schematic, connect it up, and simulate). The use of the SPICE model is transparent to the user, who gets the benefit of SPICE modeling without any changes to the way they run their simulations. I'm sure you've already guessed - but that's exactly how our software works, and also _why_ it works that way. We think combining the IBIS use model with the enhanced precision of SPICE models makes good practical sense. Todd. Todd Westerhoff VP, Software Products SiSoft 6 Clock Tower Place, Suite 250 Maynard, MA 01754 (978) 461-0449 x24 twesterh@xxxxxxxxxx www.sisoft.com Muniswara Reddy Vorugu wrote: Hi Prabhat, I have also, faced the same problem, while modeling Low-speed mode of USB1.1. Tried many options of R_fixture and C_fixture, but did not find any improvement. It looks like, we should be very lucky to get proper matching using the VT tables. To understand the cause of the inability of VT table methodology, look at slide4-5 of the following presentation. http://www.vhdl.org/pub/ibis/summits/jun03b/muranyi1.pdf It looks like; AMS-VHDL is the only solution. The above presentation contains the concept of AMS-VHDL also. Hope this helps you. Regards, Muniswar ________________________________ From: owner-ibis-users@xxxxxxx [mailto:owner-ibis-users@xxxxxxx] On Behalf Of Prabhat Ranjan Sent: Thursday, August 28, 2008 12:59 AM To: ibis-users@xxxxxxx Subject: [IBIS-Users] Dynamic behaviour of buffer Hello Experts, I have a driver with Slope control circuit at output pin. This circuit controls driver behaviour according to the Load on output pin. IBIS model of this buffer has only R_fixture but when I am simulating IBIS model with certain capacitive load then IBIS is not able to produce exact SPICE behaviour. My observation for mismatch is dynamic behavior of Slope control circuit with load which I am not able to model in IBIS. My question is how can I model the dynamic behaviour of Slope control circuit in IBIS ? Regards Prabhat -- 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.