Venu, The IBIS model will only partially for the Vcc variations. Here is how: If you lower the supply voltage, the origin of the pullup IV curve will go down to that lower voltage. So the pullup will pull up to a lower voltage. However, in real transistor circuits, this lower supply voltage would also reduce the IV curve size, because the Vgs voltage is smaller than at the normal supply voltage. This effect is usually called the "gate modulation effect" and is not reproduced by IBIS simulators to my knowledge. We are working on BIRD98 to describe this effect for IBIS models. http://www.vhdl.org/pub/ibis/birds/bird98.txt There may be two reasons for being interested in supply voltage variations. 1) Static DC characteristics of the buffer, i.e. how much will its strength change if we change the supply voltage. If you need this, you can generate several IV curves at different supply voltages and make a [Model] for each set. You can then use the [Model Selector] keyword to allow the tool to select the one you want to simulate with. 2) Dynamic noise simulations, i.e. you want to find out how the buffer will "degrade" its switching performance when there is noise in the supply voltage during its switching. This is a more difficult task, and IBIS is not doing too well on it. We have BIRD95 and BIRD98 as Lynne mentioned it already to solve this deficiency in the IBIS world. However, as usual, if you write your own models in the *-AMS languages, you can describe these behaviors to your heart's content without having to wait for BIRD95 and BIRD98. I hope this will shed some light on your questions. Arpad ========================================================= ________________________________ From: owner-ibis-users@eda.org [mailto:owner-ibis-users@eda.org] On Behalf Of Lynne D. Green Sent: Tuesday, February 07, 2006 8:07 AM To: 'Ummalaneni, Venu Babu (Venu)'; ibis-users@eda.org; ibis@eda.org Cc: 'Kotikalapudi, Shiva Kumar (Shiva)' Subject: [IBIS-Users] RE: [IBIS] To capture the delay variation with change in IO voltage Hello, Venu, Problems modeling delay changes with supply changes is a known "feature" of IBIS. The IBIS Open Forum is actively working on this. BIRDs 95.6, 97.2, and 98 are part of the solution. BIRD 95.6 was recently approved. User input is important in addressing timing issues. You would be welcome to attend the IBIS Open Forum and IBIS Futures meetings. For more info on these meetings (agenda, teleconference passcodes) please contact the IBIS chair, Michael Mirmak (michael.mirmak@intel.com). Best regards, Lynne ________________________________ From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Ummalaneni, Venu Babu (Venu) Sent: Tuesday, February 07, 2006 2:57 AM To: ibis-users@eda.org; ibis@eda.org Cc: Kotikalapudi, Shiva Kumar (Shiva) Subject: [IBIS] To capture the delay variation with change in IO voltage Hi Gurus, I have generated an IBIS model using rated IO voltage(1.5V) and simulated it at the same IO voltage(1.5V); the matching between hspice vs IBIS is very good (1st waveform in attached *.pdf). When I simulated the same IBIS model with reduced IO voltage (1.1v), the matching is poor (2nd waveform) between IBIS and hspice models. IBIS model is not able to capture the delay variation with supply voltage variation. Next, I have re-generated the IBIS model with reduced IO voltage(1.1V) and the simulation at this voltage(1.1V) gives good matching (3rd waveform) between IBIS and hspice models. Means IBIS model can not be used to see the variation in delay with the ripples on IO voltage? Is it known limitation? Are there any techniques/methods exist to build an IBIS model, which can be used to simulate at an IO voltage lesser/greater than the voltage at which it is build? Here, I am attaching a PDF of the waveforms I observed. Could some one help me in clarifying the above queries? Thanks in advance. Best Regards, Venu <<ibis_hspice_delay.pdf>> ----------------------------------------------------------------- |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 1993Received on Tue Feb 7 09:46:18 2006
This archive was generated by hypermail 2.1.8 : Tue Feb 07 2006 - 09:46:42 PST