[SI-LIST] Re: AC Coupled Signals

That's why I said it is a "theory".
A LOT of mis-designed SERDES receivers (in particular from a certain =
ASIC house) suffers from excessive pad capacitance. As a system =
designer, there is not much you can do to fix this problem at the board =
level.
This is one final desperate measure one can try.

-----Original Message-----
From: Mark Randol [mailto:Mark.Randol@xxxxxxxxxx]
Sent: Monday, September 24, 2007 1:15 PM
To: Chris Cheng; si-list@xxxxxxxxxxxxx
Subject: RE: [SI-LIST] Re: AC Coupled Signals


If I'm understanding your intent, RF designers have been doing that for
decades.  This method of impedance matching is only good over a
relatively narrow bandwidth.

For pulses, bit streams, etc, unless there's a problematic harmonic or
other component that can be treated without disrupting everything else,
perhaps not a great deal of use in the 'digital domain'.

--
Mark Randol, RF Evaluation & Application Engineer
ON Semiconductor
901 S. Mopac Expressway
Barton Oaks 4, Suite 343
Austin, TX 78746
512-329-5640 (voice), 512-329-8151 (FAX)
=20
=20

> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=20
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Chris Cheng
> Sent: Monday, September 24, 2007 2:29 PM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Re: AC Coupled Signals
>=20
> There is a theory out there that claim the AC cap pad=20
> presents itself as =3D a lower impedance and thus can reflect=20
> any impedance mismatch =3D experienced by the imperfect=20
> receiver terminator or the receiving chip =3D parasitic=20
> capacitance which can be quite off at high speed from the=20
> line =3D impedance. One can take advantage of both phenomenon=20
> by adjusting the =3D placement of the AC cap pad and thus can=20
> bounce any reflection back to =3D the terminator and help (or=20
> hurt) the imperfect termination.
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