I agree with James. Spice simulations never need to make any assumption on the values of S-parameters, and it should be same case here for IBIS analog model specification. I don't think it's necessary to include examples of how to treat special S-parameters. Matrix stamping of S-parameters are standard textbook simulation techniques. Regards, Fangyi -----Original Message----- From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of James Zhou Sent: Wednesday, March 21, 2012 10:53 AM To: bob@xxxxxxxxxxxxx; 'IBIS-ATM' Subject: [ibis-macro] Re: Analog Model Isolation Definition Hi Bob, Thanks for providing the link of past references. It is helpful for those of us who were not on the list a couple of years ago. With reference to: "the complete interface needs to be known and defined ... to get the proper gain (S21 term).", this is a proven and well-known principle in circuit and LTI network analysis. The conclusion at yesterday's meeting sufficiently satisfies this requirement. The conclusion as I interpreted was that, IBIS Specification only need to say that the Tx analog circuit input must be driven by ideal voltage sources (i.e. zero source impedance), and Rx analog circuit output must drive a load with infinite impedance. Once this is established, the Specification does not need to say anything about what goes into, or how to model, the "bigger blockbox" in the diagram (provided it satisfies other IBIS requirements such as LTI and IBIS-ISS compliant, etc.). With reference to: "In both cases, the transfer function S21 term is changed by a factor of 2...", these two cases represent total reflection by open or short circuits (S11=1 or -1). In both cases, S21 must be 0. This result is consistent with the general formula of S-parameter modeling when S11 can have arbitrary values (including the cases of S11=1 or -1). The treatment for these specific cases of open and short circuits can be provided in the Specification as examples instead of requirements of the Specification. On the issue of setting S12=0, there have been IBIS discussions or presentations recommending this. However, it is not necessary to impose this condition on the analog circuits and it should not be treated as a requirement of the BIS Specification. Regards, James Zhou QLogic Corp. -----Original Message----- From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Bob Ross Sent: Tuesday, March 20, 2012 2:57 PM To: 'IBIS-ATM' Subject: [ibis-macro] Analog Model Isolation Definition All: Per the discussion today on the block interface definition, here is a derivation based on BIRD122 for just s2p 2-ports (but should apply to s4p files with more math). It shows the gain sensitivity to the explicit S11 term for TX and S22 term for RX from a reference impedance definition (e.g., TX: S11=0 or 50 ohm to infinite impedance S11 = 1 and RX: S22=0 to zero impedance S11=-1). In both cases, the transfer function S21 term is changed by a factor of 2 (assuming no S12 term). This is equivalent to specifying the isolation interfaces with a unity gain ideal voltage amplifier. //www.freelists.org/post/ibis-macro/Eelement-in-analog-model-BIRD,1 Sorry, but some of the prior material may have involved some lost or private e-mails and also a presentation or e-mail shown to the ATM committee according to questions and exchanges in the Dec. 14, 2010 minutes including: Walter showed an email from Fangyi: - Fangyi: The equation is at the bottom - Bob: We have defined S12 as zero - The real voltage gain is a function of S11 - Todd: Is this because S11 can affect V1 and therefore V2? - Fangyi: No - If V1 was fixed V2 would still be affected by S11 - Bob: The defaults should be zero for series impedances and infinity for impedances to ground. http://www.vhdl.org/ibis/macromodel_wip/minutes/20101214/mikelabontecisco/Mi nutes%20for%20the%2012-14-2010%20ibis-atm%20meeting/20101214.txt The main point is that the complete interface needs to be known and defined in the Specification (for S-parameters and perhaps different for a SPICE model) to get the proper gain (S21 term). 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