For those who are privileged to know what I did. Two words... "follow me" -----Original Message----- From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxxxxx] Sent: Friday, August 10, 2001 9:59 AM To: Cusanelli, Tony; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Question about Simulation in Spectraquest Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit "Cusanelli, Tony" wrote: > Are you saying that you need spice simulation? IBIS will give you the delay from the output buffer to the thresholds of the > input buffer. It stops there, why do you need to go through the buffers? That delay should be included in the spec for the > part. Tony, For extremely accurate timing, the number specified by the manufacturer is not very accurate. It includes package effects. Unfortunately, even IBIS modeling (somewhat) includes package effects. As a result, there is a double counting of some of the timing and noise margin. In other cases, some of the noise and timing margin are discarded. This all depends upon the methodology used for simulation and specification. For accurate timing and noise characterization, it is best to simulate the entire path from the die to. Then the question becomes, where and how do I measure timing? Well, if the manufacturer specifies timing to the pin of the device, how do I know how he derrived this number? Did he use worst case SSO, ISI and crosstalk simulations across corners? And if he did, how do I remove these effects from my board level simulation to compensate. (This cannot be done with a standard test load, since a standard test load knows nothing of crosstalk and SSO package effects.) It turns out that the timing from die to pin of a device is heavily influenced by the noise and switching environment. Packages are highly coupled "things", much more so than PC boards, yet we often simulate without including their coupling at all. Strange, huh? This coupling from trace to trace in the package and from trace to power and ground plane is critically important to timing, jitter and noise. Yet, without a standardized way of determining how the manufacturer specified his device, we are at a loss to effectively use the information in the most accurate of ways. Even timing to the die pad of the silicon is heavily influenced by the package. However, timing at internal nodes of the silicon, such as the input to an output buffer or the output of an input buffer, are not heavily influenced by the package, since they are isolated by amplifiers. Instead, I have concluded that timing for extreme accuracy, should be performed at the input to the output buffer and the output to the input buffer, with these buffers included in the simulations. Why? Because compared to timing to the pin (or even the die) of a component, timing at internal nodes of the silicon is extremely stable and can be accurately characterized without package effects involved. Then, the remainder of the timing path can be characterized with an end to end simulation using the desired package and board characteristics, and applying the necessary data patterns to fully stimulate the system effects. In addition, noise can be added into the powers and grounds to simulate the board power environment. regards, scott -- Scott McMorrow Principal Engineer SiQual, Signal Quality Engineering 18735 SW Boones Ferry Road Tualatin, OR 97062-3090 (503) 885-1231 http://www.siqual.com ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu