As in most cases it depends. An ECL differential buffer would only have one set of waveforms with the termination voltage to Vdd - 2V. CML would also have only a rising and falling VT tables to Vdd. Most LVDS buffer models that I have seen have rising and falling to 1.25V. But a differential buffer with "normal" CMOS outputs would have rising and falling VT tables to both ground and Vdd. You can find out more about how to model by reading the IBIS cook book. 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 From: owner-ibis-users@server.eda.org [mailto:owner-ibis-users@server.eda.org] On Behalf Of shantala hegde Sent: Monday, March 30, 2009 6:40 AM To: ibis-users@server.eda.org; ibis@server.eda.org Subject: [IBIS-Users] Re: [IBIS] V-T data query Hi all, As we know, ibis model will be having two rising and two falling V-T tables. For differential buffers, (pad and padn) is it different? Do we need to have only one V-T table with Voltage source connected to VDDS? If anybody worked on differential buffer, please comment on this. Thanks in advance, Shantala On Tue, Mar 24, 2009 at 11:41 PM, Lynne D. Green <lgreen22@mindspring.com> wrote: Hello, Shantala, IBIS captures only the behavior of the buffer. Since the magnitude of the ground (and power) bounce depends on the board, it is not part of the IBIS model. There have been discussions of ways to address model response to varying Vcc-Gnd-Vee voltages. You might want to check the BIRDs and summit papers on the IBIS web site for further information. Regards, Lynne _____ From: shantala hegde [mailto:h.shantala@gmail.com] Sent: Tuesday, March 24, 2009 7:00 AM To: Lynne D. Green Subject: Re: [IBIS] V-T data query Thanks Lynne. I have one more doubt on rising/falling waveforms.I do not know much on ground bounce.But, whats the main reason for capturing v-t data with voltage source connected to ground in case of rising and vice-versa. I saw this rising/falling mismatch behaviour in pci buffers. Thanks in advance, Shantala On Tue, Mar 24, 2009 at 9:56 AM, Lynne D. Green <lgreen22@mindspring.com> wrote: Hello, Shantala, This turn on/off difference is probably designed to minimize crowbar current and power consumption. IBIS 4.x and 5.x require all V-t tables to have the same "reference" time (same clock edge). As Arpad noted, the same end time is not required in the tables. Lynne "IBIS training when you need it, where you need it." Dr. Lynne Green Green Streak Programs http://www.greenstreakprograms.com 425-788-0412 lgreen22@mindspring.com _____ From: owner-ibis@eda.org [mailto:owner-ibis@eda.org] On Behalf Of shantala hegde Sent: Monday, March 23, 2009 6:54 AM To: ibis-users@eda.org; ibis@eda.org Subject: [IBIS] V-T data query Hello all, I do have one question VT data. For example if I have an ibis model where [rising] data with voltage source connected to VDDS is a fast one.But the one which is connected to ground is slow rising. Say ,rising with vdds has 3ns and rising with ground connetced 10ns. Is this normal scenario or is it mandatory to have approximately same V-T end point for both rising/falling. Regards, Shantala -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- This message has been scanned for viruses and dangerous content by <http://www.mailscanner.info/> MailScanner, and is believed to be clean. -- 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 Mon Mar 30 09:32:41 2009
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