[sdiy] Patchell's modules

[Harry Bissell Jr]

--- karl dalen <dalenkarl at yahoo.se> wrote:
 Decoupling caps
> > are your
> > FRIENDS !!!)
> 
> Only "if" power planes are low impedance.
> If power planes are high impedance bypass caps are
> terrible enemies.
> They worsen the cirquit behaviour. So always low
> impedance your 
> powerplanes.

nah nah... they are still your friends. Its the power
supply impedance that is your enemy !!!  :^P

This is true only in very rare cases. In most cases
adding the decoupling caps lowers the power supply
impedance anyway.  

The "bite-in-the- at ss" comes if the power supply lines
are HIGHLY INDUCTIVE (like big loops of wire enclosing
a large area between current feed and return).  Adding
a cap here might possibly make the circuit RING (a
resonant condition).

Using staggered sizes of decoupling cap helps here, an
electolytic, a tantalum, and a ceramic for low to high
frequencies respectively.

Most of the ringing problems would be at very high
frequencies that the average synth-diy'er will never
see... but for RF and some high-speed computer aps
there WILL be an issue. Usually these designs use
power
planes (multi-layer boards)

This is why I run power traces FIRST (as i mentioned).
Keeping the power traces parallel to each other keeps
the inductance to a minimum.  I run -/+ voltages and
ground under each IC.

I believe my twin (Jim) does the much the same :^P

H^) harry