I'm a bit confused and in need some clarification, if anyone can help ....
In almost all circuits I've come across using integrated circuits, it seems wise - if not necessary - to place a smallish (e.g. 0.1uF) capacitor across the Vdd/Vss pins, as I understand it to stop any noise from the power supply affecting the operation of the chip (so, did I understand correctly?). That seems perfectly sensible and I can see why it's applied separately to almost every IC in the circuit .
However, I've seen that it's also common to add another, larger capacitor (e.g. 10uF) across the power supply to the whole circuit - which I'm assuming is for a similar reason (is it?). The terminology is probably wrong, but is the smaller capacitor at chip level a bypass capacitor, and the larger one at power supply level a decoupling capacitor? If not, I'd appreciate some clues as to what these terms mean.
Finally, I've also read that capacitors in parallel have an effective capacitance of the sum of the individual capacitances. So, if I have a circuit with only one IC that needs protecting, can I just use a 10uF capacitor in place of the 0.1uF? Or is there something about the nature of these two components that makes it better to put them both in parallel even if they are right next to each other? The larger capacitor is usually an electrolytic too - is that just because they offer larger capacitance or does the polarisation matter (other than making sure you've got it the right way round)?
I hope you can see my confusion?
Thanks in advance for any enlightenment ....