RE: [SI-LIST] : Re: Is feedback really EVIL?

Muranyi, Arpad (
Thu, 14 May 1998 11:47:00 -0700


I agree that IBIS can't do the detection/adjustment part of these self
buffers, but you can still handle them in IBIS through the buffer selector
mechanizm if you made a separate model for each one of the strengths the
can adjust itself to.

This will work well as long as the buffer doesn't have those wonderful
circuits. It might be a little cumbersom for the user of the IBIS model to
the selection manually, but the buffer can still be modeled.


> DC Sessions also wrote:
> >IBIS can't really deal
> >with JEDEC flexible-impedance drivers, and I'm writing THOSE into
> >the IEEE 1394b spec. Great fun. Still, we need to keep in mind that
> >the more exotic variants that you and I deal with are of very narrow
> >application.
> 4. What is a flexible impedance driver, and how does it work?

A flexible-impedance driver is one which has a drive impedance
which can be adjusted to match its load. JEDEC has a standard
in the works which addresses some of the issues involved. The
obvious method is to have a reference pin on the IC which is
tied to ground via a resistor with five times the desired
impedance. This allows well-controlled reflected-wave switching
without the component cost, board crowding, and SI compromises
of external resistors.

D. C. Sessions