IBIS Macromodel Task Group Meeting date: 07 December 2010 Members (asterisk for those attending): Agilent: * Fangyi Rao * Radek Biernacki Ansoft: Chris Herrick Danil Kirsanov Ansys: * Samuel Mertens * Dan Dvorjak Deepak Ramaswamy Cadence Design Systems: Terry Jernberg * Ambrish Varma Celsionix: Kellee Crisafulli Cisco Systems: * Mike LaBonte Stephen Scearce Ashwin Vasudevan Ericsson: * Anders Ekholm IBM: Greg Edlund Intel: Michael Mirmak LSI Logic: Wenyi Jin Mentor Graphics: * John Angulo * Vladimir Dmitriev-Zdorov Zhen Mu * Arpad Muranyi Micron Technology: Randy Wolff Nokia-Siemens Networks: Eckhard Lenski Sigrity: Brad Brim Kumar Keshavan Ken Willis SiSoft: * Walter Katz Mike Steinberger * Todd Westerhoff ST Micro: Syed Sadeghi Teraspeed Consulting Group: * Scott McMorrow * Bob Ross TI: Casey Morrison * Alfred Chong Vitesse Semiconductor: Eric Sweetman Xilinx: Mustansir Fanaswalla The meeting was lead by Arpad Muranyi ------------------------------------------------------------------------ Opens: - Arpad: We will meet Dec 14, Dec 21, and Jan 4, but not Dec 28 -------------------------- Call for patent disclosure: - none ------------- Review of ARs: - Arpad: Update Version BIRD - Done, draft 3 posted - Arpad: Update Typos BIRD - Done - Includes comments from Fangyi ------------- New Discussion: Arpad showed the Version BIRD: - Arpad: Are we ready to vote? - Would prefer to avoid discussion in this call - Mike: The Analysis section does not make clear what will go wrong without this BIRD - Arpad: Then we should discuss by email then, and not vote now - Ken: Who is the major proponent? - Are Walter and Ken in agreement? - Todd: We have mostly resolved our differences - Bob: I'm OK with this BIRD - The Version number type should be an enumerated list - We can change editorially when we adopt this - Radek: We don't need to say the version is 5.0 if AMI_Version is absent Arpad showed the Typos BIRD: - Arpad: We got stuck on the tree syntax section - Mike Steinberger had said some text belongs in a separate document - We need to describe what is allowed in the parameter string - Bob: Disagree that some parts are just "how to" and don't belong - The spec has to be complete - Terminology issues: - For example is the word "Type" a leaf? - Arpad: The word Type and the value next to it are the leaf - Bob: We are making a recursive reference to section 10 - We should keep the string contents description - Arpad: We will keep the section - Radek's comment is not included yet Walter showed sample SPICE code and Equiv Circuit Analog Model Params: - The stimulus sources are not IBIS-ISS, they are SPICE - They send a step signal into the test fixture - HSPICE tends to change time-step dynamically, resistor to ground added - The channel is a W-line - The Rx RC circuit is parameterized - Arpad: Will the BIRD have Voh and Vol for the driver? - Walter: No - This is just to generate an impulse response - Scott: This uses a lumped circuit to generate an ideal driver - Everything is at the same space and time - Walter: This is an IBIS model with: - no diff term - no C_comp - linear I/V - Ambrish: Why not let vendors use IBIS models? - Walter: Every Tx has a "framis" in it (a knob) - Every framis setting has an impedance on the Tx - It may need 128 [Model Selector]s in regular IBIS - Parameters make it much easier - Vladimir: The triangles in the diagram are not in the circuit - Walter: The triangles will be removed - Vladimir: It should have Tr and Tf parameterized - Walter: For a differential they have to be the same - It is for odd mode only - How do we generate a model when there is an s4p at the beginning and an s4p at the end - Matlab is commonly used with daisy chained s4ps - They would like to distribute them as AMI files Walter showed a presentation: - Slide 1: - The network on the left only has to be LTI - It is connected to an external network - Scott: Where does Z0 come from? - Walter: It is the on-die network ref impedance - Scott: Is the termination on-die or external? - Fangyi: The termination network is not included in Z0 - Todd: The question is whether the term is at nodes 2/4 or 1/3 - None of the energy at port 2 will make it to 1 - Scott: In a real network there is a path from 2 to 1 - Arpad: Walter should get to his next two slides - Walter: EDA tools provide the ext network - Slide 3: - These transfer function represent an LTI system - Nodes correspond to the circuit diagrams - S12 is not important because it is the back reflection - G and H are just "some" transfer functions - And inverse Fourier will get the transfer function - Scott: It assumes zero time delay - The impedance at the exit port matters - Internal s-param reflections require solution - Walter: The vendor says this is the only required math - Scott: When the electrical length becomes non-negligible the assumption falls apart - Todd: I can't agree on that fundamental assumption - Walter: The vendor is specifying this - Scott: This is a spec and we need to get it right - Take out the s-param terms for a 25 ohm channel and you get the wrong solution - Bob: Will this model support a 4 port model completely filled in? - Walter: It ignores some ports - It doesn't use S12 - Arpad: The question is if we can use an incomplete s-param model - Vladimir: The derivations we see here become invalid - Building the s-param is the vendor's business - But we should not make assumptions - We need to add the SPICE netlist to show how to include the s-param - Walter: They do not use SPICE - Vladimir: The SPICE is just to see the Z0s, not to derive - Vendors need to understand how we will use the matrix - Arpad: Is this just one way of using it? - Todd: If both the s-param ref and Z0 are 50 won't there be no reflection? - Fangyi: It has to do with how you characterize the external network - Walter: You can always convert it to the same Z0 arithmetically - Todd: Is the reflected energy zero if perfectly terminated? - Scott: This confuses the on-die network with the s-param - If it were an R network, we would be double counting - Todd: So Z0 on the left is not what the reflected wave sees - Bob: Is z0 a real termination? - Fangyi: It is the reference impedance - Todd: Z0 can't be the termination - Walter: All the reflection happens at port 2 - Scott: A 2 port would be easier to understand - Put R to gnd at port 1 - See if it works - Radek: This tries to characterize behavior with 1 transfer function - It is well defined if you know how to terminate it - Otherwise there is a problem - Walter: It appears everyone disagrees with this formulation - Vladimir: It would be unambiguous if we had the SPICE netlist - Todd: It is not clear that would be tool independent - It isn't that simple - Walter: Generating SPICE implies it has to work in SPICE - Vladimir: Not really - Walter: The SPICE circuit is simple - Vladimir: For this S11 would have to be 0 - Walter: Or -100dB - Vladimir: The Z0 on the left is not needed - Walter: Agree - Voltage swing had to be doubled for those - Vladimir: Do vendors agree with this? - Walter: Yes - Scott: It can't handle any delay - This is non-causal - Vladimir: It is causal - Arpad: Will this be a hard-coded circuit in our spec? - Ken: Hard to see why we would have hard-coded models for a specific vendor - Arpad: If we want a general purpose solution using IBIS-ISS, none of this discussion matters - Do we want to hard-code this as a common case? - Walter: A number of vendors do it this way - The AMI file can call out an IBIS-ISS circuit - But they may not do it if that is required - These two hard-coded circuits should be specified - Arpad: It should specify that the s-params not have certain portions - Do we really want to specify this specific setup? - Todd: We are all already using these - We had discussed the idea of having canned templates - This is based on Arpad's BIRDs - Scott: The problem is non-standard use of s-params - Removing half the matrix is not standard - This should not be called a TS file if it is not standard - Walter: TS is just a format, just data - Todd: Maybe we should call it something else - Maybe db-on-die - The reason to use a template is because it's convenient and common - Scott: It is a poor approximation of reality - Ken: This may not port to higher date rates - General is better - Todd: The s-param problem will still be there - The vendors are convinced this works - Arpad: This could make the spec change take a long time - Walter: This work is from 2009 - Nothing short term will change it - Scott: It's OK to have s-params with zero terms, but don't make it a template - Todd: Then we only need not explicitly say to zero out the terms - Scott: It won't work, not knowing what the term impedance will be ------------- Next meeting: 14 December 2010 12:00pm PT Next agenda: 1) Typos BIRD draft 2) Version BIRD draft 3) BIRD 121-124 discussions ------------- IBIS Interconnect SPICE Wish List: 1) Simulator directives