This tutorial came about as a result of a question I received about how to set the equalizer taps on an IBIS AMI model. I wanted some graphic way of illustrating how equalizers mitigate channel impairments (like the non-ideal impulse responses that causes inter-symbol interference (ISI)) and also what the limitations of such techniques are. I came up with a tutorial spreadsheet illustration that you can play with. You can see the spreadsheet in action in this video. Either a) Click bottom left to see it in HD on YouTube.
…or b) click here to download the MP4.
The situation behind the question was this: If you’ve ever used the ADS Channel Simulator you’ll know it supports not only IC vendor-specific models (in the IBIS AMI format) but also built-in generic IC models. The built-in generic models don’t represent a specific IC, they model industry best practices for signal processing in SERDES devices. And they include a very handy optimizer that looks at the channel impulse response and comes up a set of taps that best mitigate the ISI impairment of the particular channel.
So the first question was how much ISI can you correct with a given number of taps? The second question was what about IC vendor-specific models in IBIS AMI format? What if the vendors model doesn’t contain an optimizer? Can I relate the taps saves using the generic model to set up the AMI model?