Hi Arpad and others, I would agree what you said in general. A little clarification on IvsT table is added here. IvsT table records the TOTAL current from I/O power node (Vddq) under recommended load conditions (Arpad motioned IvsT tables describe only those "extra" current, which I would not agree with him). This total current could included crowbar current, pre-drive current, current goes out of I/O pin and others. This current table is well defined without uncertainty. In current implementation as Cisco did, these IvsT tables are used to extract those "extra" currents as Arpad mentioned. These extra currents will be load independent and they are added into existing IBIS only at the output switching points. The load-dependent reflected current asked by Mike should be well modeled by current IBIS model under ideal power supply condition. We should expect it work fine with nonideal power supply condition. The C_comp value and split ratio will play an important role under nonideal power supply condition. Thanks, Zhiping -----Original Message----- From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Muranyi, Arpad Sent: Friday, October 14, 2005 10:43 AM To: ibis@eda.org Subject: RE: [IBIS] [Composite Current] with series termination Mike raised a very interesting and good question. If I may rephrase it, this is what he asked: Since the output and supply current profile is also effected by the length of the transmission line, are the I(t) tables of BIRD95 going to work in practice when people will use the buffer model with all kinds of transmission line lengths? My hand waving answer to this is as follows. The reason I am saying hand waving is because I didn't test this, so I can't tell for sure. The I(t) tables seem to describe only those "extra" currents which are happening when the buffer is switching. (Crow bar, pre-driver noise, etc...). This is not longer than the length of the Vt curves in duration. After the buffer is done switching, the currents are completely determined by the IV curve and the voltage on the pad. Therefore, since the buffer is in the "steady state" when the reflection comes back from the end of the T-line, it shouldn't really matter when that happens. Is my thinking correct? Could anyone try this (Sam, Zhiping) to prove it? Thanks, Arpad =================================================================== -----Original Message----- From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Zhiping Yang (zhiping) Sent: Thursday, October 13, 2005 2:05 PM To: Mike LaBonte (milabont); ibis@eda.org Subject: RE: [IBIS] [Composite Current] with series termination Hi Mike, I might not understand your questions completely. Here is what I can think about it. First, the composite current will be specified only under certain load conditions and it is the total current. In the integration of composite current into IBIS implementation, it is not simple addition of composite current to IBIS model, it has to be pre-processed and the added current will be the difference between composite current and pure IBIS model current. For the case you specified, the BIRD95 will improve the accuracy at the rising/falling edge. The constant 25mA current after rising/falling edge should be able to taking care by existing IBIS simulator. Please call me if you still have any further questions. Thanks. Best regards, Zhiping -----Original Message----- From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of Mike LaBonte (milabont) Sent: Thursday, October 13, 2005 10:25 AM To: ibis@eda.org Subject: [IBIS] [Composite Current] with series termination I would like to ask the simulator gurus out there how the BIRD95 [Composite Current] waveform would be used with series termination, ie. reflective switching. With a 2.5V series terminated 0.5ns buffer driving, say, a 2ns, 50 ohm transmission line, the pad voltage rises to 1.25V, stays there for quite a while, then completes the rise to 2.5V. During the 1.25V period the pad current will be flat at about 1.25/50 = 25mA. This pad current flattening begins about half way through the "normal" rise time, as measured using the standard test fixtures. At that point the pad current flattens out at 25mA, but the [Composite Current] is telling the simulator the VDDQ current needs to continue dropping to zero. Here are the 3 currents I see in a rising edge simulation of such a test fixture. Sorry, I can't make the 3 curves add up to zero at all points using ASCII graphics: Pad current : -50 --- reflection back to driver here | v _______________________________________/\ / \ / \ 0 ___ / \_____________ VDDQ current : /\ 50 --- | | | | | | | \_______________________________________/\ | \ | \ 0 ___ / \_____________ GND current : -50 --- /\ | | | | | | | | 0 ___ / \_______________________________________/\_______________ [Composite Current] probably looks like this : /\ 50 --- | | | | | | | | | | | | 0 ___ / \________________________________________________________ My question is, will the simulator deliver the constant 25mA current at the pad for several nanoseconds if it is being told that VDDQ current is a spike that drops to zero at the end of the 0.5ns "normal" rise time? This may have come up before, but if so I haven't heard it put quite this way. Mike LaBonte ----------------------------------------------------------------- |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 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 Fri Oct 14 11:13:19 2005
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