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C-comp and output risetime

Question asked by david.royle on Jun 23, 2011
Latest reply on Dec 7, 2012 by david.royle

We have discovered that with Hyperlynx 8.0 the output rising edge is dependent on the value of c_comp. From what I understand this is wrong.

We are modeling an Altera Arria IIGX part (LVDS) and if we set c_comp = 0pf then its simulated rising edge matches precisely the measurement made with 12GHz scope (200ps).

However, the Altera IBIS model calls out a 7pf c_ comp which slows the simulated rising edge down to 400ps. In other words it looks like Hyperlynx is double counting c_comp,  its effect has already taken into account in the V-T curve. I thought it was well understood that c_comp needs to be visible from the outside looking in, but invisible from the inside looking out. I have verified that 8.0 causes this behavior with other LVDS drivers as well (DS90LV049). Is this a bug in this particular version?

I have attached a doc that does a reasonable job of describing why c_comp value should not alter launch waveform.

Dave

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