Actually, for audio systems, the time variant behavior of a capacitor is extremely important. Capacitors that do not have good structural integrity exhibit microphonics in an audio system.
Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC Brad Brim wrote:
Is a decoupling capacitor on a board LTI? Most of us would answer "yes".However, capacitors vary with temperature to imply time variance. Capacitors also vary with DC bias voltage, which implies an underlying large signal nonlinear behavior. Capacitors vary with age, again implying time variance. Seems to me the issue was expressed quite well in the last meeting as one of "time constant" and what we wish to consider in analyses. The time constant of signals is picoseconds or nanoseconds. What time constant bounds do we wish to consider in our analyses? If it's on the order of temperature variations, then temperature certainly becomes a time varying parameter. Do we believe it will be required in the foreseeable future to consider passive interconnect as time varying or nonlinear in our system/channel/component analyses with this time constant issue being fully considered? If not, then temperature, bias voltage and other such parameters become higher level discrete state controls rather than low level continuous parameters? regards,-BradBrad BrimSigrity, Inc. 4675 Stevens Creek Blvd, Suite 130 Santa Clara, CA 95051 408-260-9344 ext 147 503-628-6230 (alternate) 503-799-9917 (mobile) bradb@xxxxxxxxxxx <mailto:bradb@xxxxxxxxxxx>------------------------------------------------------------------------ *From:* ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] *On Behalf Of *Muranyi, Arpad *Sent:* Thursday, June 26, 2008 2:02 PM *To:* IBIS-ATM *Subject:* [ibis-macro] Re: Question on seeting the EMD direction In our recent discussions on Interconnect-SPICE and our last IBIS-ATM teleconference the question was raised whether we can safely assume interconnects are LTI. Scott's message below (from a different thread) seems to indicate that there are situations when this may not be the case. This makes me nervous about writing a specification that by its definition would disallow those effects to be simulated... Any comments?Arpad=============================================================== ------------------------------------------------------------------------ *From:* Scott McMorrow [mailto:scott@xxxxxxxxxxxxx] *Sent:* Thursday, June 26, 2008 2:03 PM *To:* Muranyi, Arpad *Cc:* twesterh@xxxxxxxxxx; msteinb@xxxxxxxxxx; wkatz@xxxxxxxxxx; huangchunxing@xxxxxxxxxx; IBIS-ATM; guantao@xxxxxxxxxx *Subject:* Re: [ibis-macro] Re: IBIS-AMI Arpad I agree with you, and would add that even the analog network characterization portion of a passive interconnect system is not a well understood topic. Several issues come to mind: * Time variance of the interconnect due to: o Temperature o Humidity o Mechanical Vibration (think twin-ax cables in a vehicle) * Equalizer training in the presence of crosstalk and noise spikes in a hot-plug environment But heck, I'd settle for an IBIS-AMI model that correlates with something that can actually be measured. Scott Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLCMuranyi, Arpad wrote:Sorry to everyone for arguing a little on what has been stated so far. I tend to disagree with the statement(s) that the analog corner modeling is a well understood topic. Just because it is common practice to use high/low supply voltages with low/high temperatures, etc... to achieve best/worst timings, it doesn't mean that this practice actually gives the best/worst timings. Having done large amounts of parameter sweeps while I was working for my previous employer, I saw solution space plots which had failing islands corresponding to "in-between" parameter values, and not at the extremes. The answer then was that we do not know where the system is failing unless we simulate all possible combinations of parameter values. That's when the frequency domain (resonance) analysis, sensitivity analysis, design of experiments (DOE) and similar techniques became popular. I tend to believe that the application of statistical analysis techniques is a natural continuation of this evolution, as kind of an attempt to reduce the amount of time it takes to go through all possible parameter combinations... My $ 0.02 worth... Arpad ===========================================================-----Original Message----- From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff Sent: Thursday, June 26, 2008 1:00 PM To: msteinb@xxxxxxxxxx; scott@xxxxxxxxxxxxx Cc: wkatz@xxxxxxxxxx; huangchunxing@xxxxxxxxxx; 'IBIS-ATM'; guantao@xxxxxxxxxx Subject: [ibis-macro] Re: IBIS-AMI It's worth pointing out an IBIS-AMI model actually has two models - - the analog model in the .ibs file, and - the algorithmic model pointed to by the .ibs file IBIS-AMI analysis separates analysis of a link into two stages - network characterization and link analysis. The analog model is used for the former, while the algorithmic model is used for thelatter.When we talk about modeling PVT variation, it's worth considering how PVT affects each type of model separately. Modeling the effects of PVT on a transmitter's output stage or a receiver's input stage is well understood (it's what IBIS has been doing for years), while modeling the effects of PVT on equalization behavior is [relatively] new ground. I agree this is something we should consider standardizing, and I also agree that we need more experience in this area before it makes sense to try & put such standards in place. Todd. Todd Westerhoff VP, Software Products SiSoft 6 Clock Tower Place, Suite 250 Maynard, MA 01754 (978) 461-0449 x24 twesterh@xxxxxxxxxx www.sisoft.com
