> If you used any poly metal foil or electrolytic caps then they have
> long foil wound around each other for plates and this then creates an
> inductance scenario and possible parasitic resonances. So look at your
Thanks for your response. I am just wondering home come a lot of
people using QSD don't encounter these nasty problems. I avoided the
electrolytic caps all together. If I made a list of type of
capacitors, would you be able to sort a couple of recommended and
totally not recommended
Tantalum dipped
Polyester
Metallized polyester
Metallized polypropylene
PPS film
Foil
Polypropylene film
ceramic disc
interference suppression X1 X2
MLCC
monolithic c0G
monolithic X7R
monolithic Z5L
My PCB is two sided. I don't have a ground plane around the two 7805s,
so that is probably very bad and will most definetely go in version 3
of the board. Right now, I am working on a fresh predrilled whole so I
can focus purely on the parasitics. The caps I put there are all
tantalum and ceramic disc, but to be honest I was naive and didn't
expect a problem.
Leon,
I looked at notch LC circuits and had a problem with my 64MHz
oscillator module source. I put R=10ohm, L=0.49uH C=12pF to get a
Q=wL/R=19. The oscillator didn't run with the 10ohm drive impedance
and I didn't put a common collector NPN follower yet. To get the
target 64Mhz I am kind of wondering if I should decrease the Q with a
smaller inductor or if I should put an adjustable trim cap and play
until I get the right frequency.
Frank
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