As you know, coupling capacitors are used to minimize ripple in
batteries/power supplies. This is important, because even the
slightest ripple can cause an IC to behave incorrectly.

I understand the role of ceramic capacitors. Ceramic capacitors are
used to couple RF ripple and thus minimize RF interference. .1uF
seems to be a popular value. At 1.8MHz, the capacitive reactance of a
..1uF capacitor is .884 ohms, and the ESR is usually a small fraction
of an ohm and not significant.

I have also seen circuits that use smaller value capacitors. What's
the point of .01uF and .001uF coupling capacitors? Is the stray
inductance THAT much lower? I have 1uF 50V monolithic ceramic
capacitors (JIM-PAK MD1), and they're actually smaller than my .1uF
50V ceramic disc capacitors (DC.1). Why doesn't everyone just use 1uF
ceramic capacitors for power supply coupling? At 1.8MHz, capacitive
reactance of a 1uF capacitor is only .0884 ohms.

What's the point of relatively low value electrolytic capacitors?
Their ESR values are usually on the order of 10-100 ohms. At 60Hz, a
1uF capacitor has 2650 ohms of capacitive reactance. A 10uF capacitor
has a capacitive reactance of 265 ohms, and a 100uF capacitor has a
capacitive reactance of 26.5 ohms. Given this, shouldn't all
electrolytic capacitors be at least 100uF? Is there any point to a
1uF electrolytic capacitor when there are 1uF ceramic capacitors that
have the advantages of lower ESR and nonpolarity? (Connecting an
electrolytic capacitor the wrong way will cause its internal material
to boil out and make a big mess. Connecting a tantalum capacitor the
wrong way will start a fire!)

Jason Hsu, AG4DG
usenet AAAAAATTTTTT jasonhsu.com