Re: [SI-LIST] : Transient impedance

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From: sweir (weirsp@a.crl.com)
Date: Tue Nov 16 1999 - 09:25:12 PST


Sandy,

Can you point to any existing papers on linearized output impedance, and
any ASIC mfgs currently offering this? Thanks.

Regards,

Steve.
At 05:48 PM 11/15/99 -0800, you wrote:

>"D. C. Sessions" wrote:
>
> > As a general rule, ...
>
>I never did like general rules.
>
> > we design output stages to keep the crowbar current low.
> > Break-before-make, as it were, although it's no exactly sequenced so much
> > as just turning off faster than on. Necessarily, though, the output goes
> > through a high-impedance point.
>
>When signal fidelity is critical quite a bit can be done to make cmos circuits
>behave better. As you "feel the need for speed" you can add:
>
>- slew rate control
>- linearized output impedance (~constant output over varying output voltage)
>- impedance control over PVT, matching an external resistor
>- smooth break as make to maintain constant impedance during switching.
>
>The good news (for the chip designers) is that the mos devices are improving
>faster than the bus speeds increase. This gives us more flexibility to add
>full blown analog circuits on the IO pins. More on this at ISSCC,
>including some schematics.
>
>Sandy Taylor
>CMOS Solutions
>
>
>
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