At 09:30 PM 1/13/01 -0700, Jose S. Samonte Jr. wrote:
>Sir David, so what is the advantage of using a decoupling capacitor over not
>using one? When does the PIC need the short bursts of current and why?

The short version: You will have all sorts of bizarre problems without it.


Anything that uses lots of MOS gates, has lots of capacitors internally.
These capacitors are the MOS input gates.  Every time the machine changes
state, hundreds or maybe tens of thousands of these capacitors are charged
or discharged.

MOS gates, in theory, draw nothing at all when not switching, and most
modern MOS products come pretty close to that ideal. The difference between
sleep and full speed operation is literally the charging and discharging of
all those caps.

Also, it is typical that they change state in bunches, rather than more or
less at random. This makes the current drain "spiky", and we need to supply
that current during these intervals, so that the input voltage dosen't move
around enough to change the logic thresholds, or stop parts of the chip
from working.


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