RE: [linux-audio-dev] Writing a driver for this card: your thoughts?

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Subject: RE: [linux-audio-dev] Writing a driver for this card: your thoughts?
From: Richard C. Burnett (burnett_AT_tality.com)
Date: Fri May 31 2002 - 17:39:32 EEST


Thought I would chime in just for some extra information in case anyone
cared to know. As the feature size of chips keeps getting smaller and
smaller, these same issues are getting increasingly worse! At 0.18 signal
integrity doesn't always have to be checked if you are careful with your
rise and fall times for digital signal (plus your fanout), but as you go
to 0.13um feature size, the capacitive effects start to cause big signal
integrity problems. It is interesting to me that these problems are a big
problem at the board level too, I didn't know that.

Rick

On Thu, 30 May 2002, Bob Colwell wrote:

> Somehow I feel the need to get even more specific.
>
> Voltage sags for two reasons: DC resistance and AC impedance.
> DC resistance is just plain old ohms law -- no perfect conductors
> exist (until the folks in the labs give us high-temp superconductors),
> so a current flow will always cause a voltage drop, as in E=IR.
>
> AC impedance matters because conductors also exhibit inductance and
> capacitance. Capacitance causes signal leakage and cross-coupling.
> But inductance causes AC-induced voltage spikes, because coils
> convert electrical energy into a magnetic field, and if you try to
> collapse that magnetic field quickly (as a fast-changing electrical
> signal does) it reconverts back into an electrical potential that
> acts to oppose the change in current. If one distributes capacitors
> of the appropriate size and speed, one can effectively decouple
> the downstream inductances from the current spike.
>
> Lamar knows all this but I thought it might benefit others who might
> not. -BobC
>

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