All, I had one more query for open-drain cells for a buffer driving a huge capacitive load (bus capacitance) For ex: a slow buffer with a large fall time How do we model V-T data for such buffer. As we have only pulldown clamp currents and RISING and FALLING WAVEFORM with R_Fixture tied to actual pullup resistor(and not 50 ohms) connected to V_FIXTURE= VCC. Should we have C_FIXTURE (bus capacitance) define for V-T data. What i feel is as the buffer's fall time is so huge, there is no such Transmission line modelling required for such a case. Thanks and Regards vinayak Vinayak Ghatawade wrote: > All, > > Thanks for the information and replies. > The buffer is using a feedback which changes the drivestrengths. > > Currently we are going to chop the ringing portion > of the IBIS V-T data which looks the safer option > and go ahead. > > Thanks again > vinayak > > Muranyi, Arpad wrote: > >>Andy, >> >>You are absolutely correct, there are different >>types of feedbacks, and I should have defined >>which one I was referring to in my posting... >> >>I was thinking of one that adjusts the drive >>strength real time as the buffer is switching. >>Legacy IBIS can't do that. (Although one could >>model these too using the *-AMS extensions of >>IBIS). >> >>On the other hand, buffers which adjust their >>own drive strength only once and a while to >>compensate for temperature variations, for >>example, can be modeled in IBIS as if they were >>normal buffers, because they don't change skins >>while driving signals onto the bus. You may >>need the [Model Selector] keyword to make a >>few different driver models available for the >>various strengths, but that's all. >> >>Arpad >>------------------------------------------------ >> >>-----Original Message----- >>From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Andrew Ingraham >>Sent: Wednesday, January 04, 2006 9:31 AM >>To: ibis-users@eda.org; ibis@eda.org >>Subject: [IBIS] Re: hspice vs IBIS model correlation at different capacitive loads >> >> >> >>>I think he is saying that the oscillations happen >>>because of the feedback in the buffer is trying to >>>settle to a steady state condition. >>> >>>If so, legacy IBIS can not model your buffer, since >>>there are no provisions for describing feedback. >>> >>> >> >>Yes. >> >>Although it depends on the feedback. >> >>Linear negative feedback, such as used on op-amps to reduce output >>impedance, should work OK, I think. It's probably also possible that some >>forms of feedback to reduce variations in drive strength (for example), >>ought to be somewhat compatible with conventional IBIS. But things like >>positive feedback to give hysteresis, don't play well in IBIS. >> >>Regards, >>Andy >> >>----------------------------------------------------------------- >>|For help or to subscribe/unsubscribe, email majordomo@eda.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 email a request to ibis-request@eda.org. >>| >>|IBIS reflector archives exist under: >>| >>| http://www.eda.org/pub/ibis/email_archive/ Recent >>| http://www.eda.org/pub/ibis/users_archive/ Recent >>| http://www.eda.org/pub/ibis/email/ E-mail since 1993 >> >> > |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just 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 email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993Received on Mon Jan 9 07:54:42 2006
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