Be careful. IBIS uses the manufacturer's specified Vinh and Vinl. They are the points where the part is guaranteed to switch. As Arpad points out the actual switching point could be different and very well changes with temperature, voltage and process though modern manufacturing processes make the actual switching points more consistent from part to part. Timing should be measured to the points that are in the datasheet. But having all simulators default to some arbitrary state when the input is between the reference levels is setting the user up for failure. People tend to assume if the simulator says X, X is real. If they don't see X in the real circuit then there is something wrong. Not all parts will conform to some arbitrarily designated state. Digital parts are not made to operate with their inputs between Vinh and Vinl. Most parts have specifications that state the minimum slew rate (input risetime/falltime) as the input to the part transitions between the two reference levels. The actual output of an input buffer for a given input voltage between Vinl and Vinh will change depending on the internal noise of the IC, the noise on the input, process, temperature, voltage, phase of the moon, crosstalk, etc. Tom Dagostino Teraspeed(R) Labs 13610 SW Harness Lane Beaverton, OR 97008 503-430-1065 503-430-1285 FAX 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@server.eda.org [mailto:owner-ibis@server.eda.org] On Behalf Of Akhilesh CHANDRA Sent: Friday, January 04, 2008 12:23 AM To: 'Muranyi, Arpad'; ibis@server.eda-stds.org; owner-ibis-users@server.eda.org; ibis-users@server.eda.org Cc: Akhilesh CHANDRA Subject: RE: [IBIS-Users] RE: [IBIS] RE: IBIS model behaviour between Vinh and Vinl input Hello Arpad, I got your point. As I understood IBIS model of a receiver is measurement model. it compare the incoming waveforms against Vinh and Vinl. If it is above Vinh, we have a logic "1" ("true"), if it is below Vinl, we have a logic "0" ("false") and between vinh and vinl it have logic X. IBIS specs don't define that how logic X represent in IBIS simulation, due to this different simulator give different behavior for X. In my view we will need to define how logic X represent in IBIS model simulation. It will help to align all the simulator results. Regards Akhilesh -----Original Message----- From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of Muranyi, Arpad Sent: Friday, January 04, 2008 12:34 PM To: ibis@server.eda-stds.org; owner-ibis-users@server.eda.org; ibis-users@server.eda.org Subject: [IBIS-Users] RE: [IBIS] RE: IBIS model behaviour between Vinh and Vinl input Akilesh, I don't think you understood my previous answer. On the other hand, I am not sure I understand everything you say either, so I will attempt to describe it once again. Let me know if I didn't answer your question, but please be a little more crisp with your words, because I have a hard time to understand what you are writing. A SPICE receiver model will give you a WAVEFORM on its output. This waveform will be a smooth waveform. It will switch states when the input goes over the threshold value of the input amplifier. This threshold voltage is not the same as the IBIS Vinh and Vinl parameters. In the good old 5 volt days the receiver could switch a few hundred mV around 1.5 volts, while the TTL specification was 0.8 and 2.0 volts for Vinl and Vinh. The specification was usually set to a wider range than the actual threshold for various reasons. In IBIS we don't model the actual threshold behavior of the receiver. (You could if you used [External Model], but that is a different story). The IBIS receiver is really nothing more than a measurement model. It doesn't simulate the receiver's actual reactions to the incoming waveform, and most importantly it doesn't give you an analog waveform that resembles the output waveform of the actual receiver. You can consider the output of the IBIS receiver as a logic output of an ideal comparator, comparing the incoming waveforms against Vinh and Vinl. If it is above Vinh, you get a logic "1" ("true"), if it is below Vinl, you get a logic "0" ("false"). The transition is abrupt, theoretically with a perfectly vertical edge. Do not expect to see a smooth waveform here. Since most IBIS simulators represent the output of a receiver as a waveform, you will most likely get a 0 volt or a 1 volt signal instead of a logic "true" or "false". But the meaning is the same. The remaining question is what should the output of the receiver be when the input waveform to the receiver is between Vinh and Vinl. The problem is that the IBIS specification doesn't describe this in great detail. If we go by the example that is in the IBIS spec, where the comments say the following: Vinl = 0.8V | Input logic "low" DC voltage, if any Vinh = 2.0V | Input logic "high" DC voltage, if any we could conclude that anything in-between Vinh and Vinl is neither logic "high" or "low", i.e. it is an undetermined state "X". I have seen implementations where the output of the receiver would switch when the waveform goes above Vinh on a rising edge, and goes below Vinl on a falling edge. This gives you a hystersis type result which is not necessarily correct, because the receiver may lose its valid logic output as soon as the input waveform enters the region between Vinh and Vinl. I personally prefer the undetermined state on the output of the receiver "X". But how can this be represented in an analog simulator which gives us a 1 or 0 volt output? In that case I would suggest that the receiver's output should go to 0.5 volt when the input waveform is between Vinh and Vinl, indicating that this is the undetermined condition "X". I hope this helps, Arpad ======================================================================= -----Original Message----- From: Akhilesh CHANDRA [mailto:akhilesh.chandra@st.com] Sent: Thursday, January 03, 2008 9:45 PM To: Muranyi, Arpad; ibis@server.eda-stds.org; owner-ibis-users@server.eda.org; ibis-users@server.eda.org Cc: Akhilesh CHANDRA Subject: RE: [IBIS] RE: IBIS model behaviour between Vinh and Vinl input Hello Arped, Thanx for your reply. In the design spec output can't switch between vinh and vinl values. And we run simulation with spice then design behave same way and give smooth transition as the device does. I am using ELDO as simulator to run the IBIS simulation it show horizontal line (other simulator show different result) between vinh and vinl values it shows mismatch between IBIS and spice behavior. Do you think the behavior of simulator is correct. In my view we will need to define IBIS behavior between vinh and vinl values otherwise each EDA vendor do it by his own algorithm and it create confusion at the application end. Regards Akhilesh -----Original Message----- From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On Behalf Of Muranyi, Arpad Sent: Thursday, January 03, 2008 9:47 PM To: ibis@server.eda-stds.org; owner-ibis-users@server.eda.org; ibis-users@server.eda.org Subject: [IBIS] RE: IBIS model behaviour between Vinh and Vinl input Akilesh, A SPICE model does what the device does (more or less). An IBIS model's Vinh and Vinl does what the input specification tells you when you look at a SPICE waveform and try to decide whether the waveform you got was good enough to consider logic high or logic low. IBIS does not describe how the device behaves between Vinh and Vinl. Arpad ================================================================= -----Original Message----- From: Akhilesh CHANDRA [mailto:akhilesh.chandra@st.com] Sent: Thursday, January 03, 2008 4:22 AM To: ibis@server.eda-stds.org; Muranyi, Arpad; owner-ibis-users@server.eda.org; ibis-users@server.eda.org Cc: 'akhilesh chandra' Subject: IBIS model behaviour between Vinh and Vinl input Hello Experts, I am using IBIS model of hysterics cell. In my model Vinh and Vinl have different values as per design specs. When I run it with one of the simulator then it show output at constant voltage(VDDE/2) between Vinh and vinl inputs, while spice show continuous behavior with same simulator so there is big mismatch between IBIS and spice result. Can anyone explain us what IBIS standard say about output behavior between Vinh and Vinl input values. Regards Akhilesh -- 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 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 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 Jan 4 01:37:56 2008
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