[SI-LIST] : Re: Controlling switching noise in full-swing CMOS buffers (was Despite output resistor to reduce overshoot and undershoot)

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From: Wai-Ming Hung (whung@pericom.com)
Date: Wed Dec 06 2000 - 09:36:02 PST


Hi Patrick,

> If you have the ability to influence the pre-drive stage,
> then I'm assuming you're designing your own buffer.

Yes, I am designing the buffer.

> #5) Linear output impedance: The end goal is not necessarily
> to reduce noise, but is to improve signal integrity. To
> do this, you might consider some form of linearizing circuit
> on the final output stage. Most generic buffer designs
> have simple PMOS-NMOS ladders as the final stage, and
> their respective output impedances vary dramatically depending
> upon the output voltage (governed by the I-V curves).
> There are a few ways to linearize the output impedance such
> that it stays relatively flat over the bulk of the output
> voltage range. Sorry I cannot share circuits with you
> (proprietary to others or me), but if you have the time,
> it's worth looking into.

I do not quite understand why linear output impedance can reduce noise
or improve
signal integrity ? You do not need to share the circuits anyway :)
Are u talking about the dynamic output control implemented by some large
companies ?
If so, actually I also thought of this but perhaps as u said, it is a
kind of proprietary, so I have
to figure out the other way round.

>
> Hope this helps,
> Pat
>
> > Hi
> >
> > Despite the fact that I can use resistor to reduce output noise,
> > are there other novel ways such that I need not compensate the
> > output level while still can reduce noice, Or can I do sth in the
> > pre-drive stage before the output stage ?
> >
> > Thanks alot
> >
> > Kenneth
>

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