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

Muranyi, Arpad (arpad.muranyi@intel.com)
Thu, 14 May 1998 11:47:00 -0700

D.C.,

I agree that IBIS can't do the detection/adjustment part of these self
adjusting
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
buffer
can adjust itself to.

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

Arpad
============================================================================
===

> 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
dc.sessions@tempe.vlsi.com