It is always a good idea to have a large C and then decouple other parts of the circuit locally with high frequency smaller C's, especially close to any I.C.s. But also the layout of the PCB is crucial if you want low noise / high frequency / to avoid psu oscillations. In my experiance you can't beat having a ground plane for 0V, which you only break to allow component legs to go through. The power rails should also be reasonably big tracks / wires but how you do this depends on your circuit board method of construction.
The reason small caps are used is that they have a higher resonance frequency. Every cap has INDUCTANCE which means its a series resonant tank. Above the resonant frequency, the cap impedance rises quickly. At the highest frequencies, the PCB ground planes are the most effective supply caps. Simply connecting to a capacitor adds inductance so the best PCB layout tries to place them symmetrically in an effort to cancel the inductance of the traces and vias that connect the capacitors. If the connection inductance dominates, then there is no point in using smaller caps.
http://qandasys.info/how-to-place-decoup...
http://www.xilinx.com/support/documentat...
It would be better to alter the types of capacitors. Say mylar, ceramic, and electrolytic, so the frequency responses can help you out.
I would put a ferrite core around the two "power supply input leads", this will help reflect RF noise back into the power supply.
Power supply filtering is always a function of what is being powered.
Too much capacitance can be very bad in any circuit where it is not needed.
If you are driving any IC it is usually designed to reject 10mv of noise.
You probably only need a 10uF tantalum power cap and a .1uF ceramic cap. Cap overkill is the din of electronics. Good filtering is an art, overkill is a disaster.
5 ohm resistors will do almost nothing , but tiny inductors that measure one or two ohms may be helpful in reducing higher frequency noise. I suggest 0.001uf = one nanofarad, for your first capacitor.
Capacitors are cheap, so I want to use them liberally. If a low noise circuit has even less noise, that's a good thing right?
The power supply provides 3.3V and it's already a clean supply. What I can't say for sure is how clean it is and if any noise gets in there before it reaches my circuit. So I thought better add some capacitors just to be save. What I have drawn up is pretty simple. I figure, start with a low value capacitor for high frequency noise and work my way up. At the end I have a 10uF that is not going to be for noise but more like a reservoir. The circuit will draw somewhere around 100 mA. I have 2 questions:
What I have, does it make sense, like do I even need 0.01uF?
Should I add a low value resistor (like 5 Ohm) in series or is that a bad idea?
