Walter, I would like to encourage everyone to use crisper language in this conversation to avoid these kinds of confusion. An “output” is not driven by anything, otherwise you have two outputs connected which is a contention. Logic simulators don’t even allow you to make such connections, it is an error. It seems that you mean an “an output buffer’s input is driven by something – it’s stimulus”. Regarding “So there is never a need to do a SPICE simulation from the channel Tx to the channel Rx through the retimer or redriver.”, I don’t want to put words into the mouth of the person who asked the question, but I don’t think that the motivation was channel characterization. One could potentially use these repeater analog models for normal legacy simulations as well, and it seems that it would be convenient to define how the Rx output goes into the Tx input of a repeater analog model. I tend to agree with the rest of your comments about the need for defining a few more things in Fangyi’s proposal as I described it in my previous posting on this thread. Thanks, Arpad ======================================================================== From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz Sent: Wednesday, March 13, 2013 1:09 PM To: Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx Subject: [ibis-macro] Re: redriver in spice simulation Arpad, Of course an output is driven by something – it’s stimulus. In the case of a redriver, the stimulus is a continuous waveform. In the case of a retimer the stimulus is a “digital” waveform that transitions between -.5 and +.5. There are no constraints on the voltage range of the stimulus input to a redriver output. Note that both a redriver and a retimer are “repeaters”. As far as SPICE simulation with a redriver or retimer (the retimer flow is identical to a redriver flow, except that jitter can be inserted by the EDA tool in a retimer), the requirement is that the EDA tool generate an impulse response from the initial Tx to the Repeater Rx, and a separate impulse response from the repeater Tx to the next Rx. The is two separate SPICE simulations (if you choose to do SPICE simulations to generate the two impulse responses). So there is never a need to do a SPICE simulation from the channel Tx to the channel Rx through the retimer or redriver. I stated before, and I repeat my concern that the EDA tool does need to know how to generate the impulse response from redriver Tx to the channel Rx, and the Redriver BIRD is not clear on how to do this. Since the redriver Tx is a true analog circuit it can be represented by an s4p (BIRD 158), and if the analog circuit is defined using BIRD 158 generating this impulse response is trivial and can be done using SPICE or S parameter arithmetic (assuming the RX is LTI). Because the redriver Tx is an analog object it cannot be represented by a legacy IBIS model or a BIRD 116 External Model (which has a D/A converter). Walter