On Tuesday 13 April 2004 21:54, Byron A Jeff wrote:
> On Tue, Apr 13, 2004 at 09:45:10PM +0100, Matt Marsh wrote:
> > Hi,
> >
> > I've seen a number of circuits where a capacitor is placed
> > between the VSS and VDD pins of the PIC.
>
> Of course.
>
> > Is this something that should always be done?
>
> Of course! ;-)
>
> > What is the purpose of this capacitor?
>
> Bypass capacitor. Some quick cap theory. In short it blocks fixed
> DC signals and allows variable signals to pass across the cap.
> Clearly the VSS/VDD connection should be as DC as it gets. But in
> fact there's a lot of noise on power supply lines that can affect
> circuit operation. So one purpose of the bypass cap is to create
> a low impeadance path to eliminate noise on the power supply
> lines.
>
> The second item is that many modern circuits that utilize CMOS
> technology will draw significant spikes of power when switching.
> So at each clock edge you'll get a bit of a voltage dip. Bypass
> caps can provide additional power in those dips.
>
> So in the end bypass caps stabilize your power supply to your
> chips reducing the amount of noise on those power supply lines.
>
> Sprinkle liberally.

Thank you! And yes, this is all making sense now along with the
article Jan-Erik pointed me at :-)

Thanks for the help, I clearly need to learn a lot more about basic
electronics theory :/

Matt

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