RE: [SI-LIST] : A Basic question.

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From: Michael Nudelman (mnudelman@tellium.com)
Date: Mon May 14 2001 - 06:24:20 PDT


Rahul:

AC term (or what's generally know as AC term) is a kind of parallel
termination, the particular feature being that while DC term is, simply put,
a matching (to the line impedance) resistor connected to the end of the TR
line and a voltage source (typically between GND and VCC), the AC term is
the same resistor connected to the GND (or VCC- does not really matter)
through a cap.

This way the AC term does not load Power supply and loads driver only during
the transition.

The AC term is good for clocks (periodic signals) where the cap is charged
to 1/2 of the VCC and this way requires the driver to provide current no
larger than Thevenin (split DC) terminator.

However, for non-periodic signals (data, strobes, short clock bursts (like
CAS- in the DRAM) etc), the AC term requires the driver to pump twice the
current, and this way some drivers may be unable to adequately perform.

Mike.

-----Original Message-----
From: whiz kid [mailto:we_r_frendz@yahoo.com]
Sent: Sunday, May 13, 2001 11:06 PM
To: si-list@silab.eng.sun.com
Subject: [SI-LIST] : A Basic question.

Hi SI Gurus,
What is the use of AC termination. where is it used.
Cant we use source or parallel termination instead of
AC termination.

Thanks in Advance.
Rahul.

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