I wonder about wisdom of paralleling ceramic decoupling capacitors. I some old text I have found advice to use 10uF (electrolytic), 100nF and 100pF in parallel. Several relatively new text write about combinations like 1uF and 100nF, both ceramic.
In case of electrolytic capacitors things seem clear: electrolytic is mostly resitive in middle of frequency boound and ceramic gives pure improvement. However, datasheets of modern ceramic capacitors suggest that ESL is almost independent of capacitance (ESL groves with size but in given size seem to vary only a little). Simple RCL model shows that parallel ceramics will have parallel resonace peak when capacitance differ enough (about 3 times for modest peak, 10 times gives substantial peak). Parallel combination will have smaller impedance above self resonant frequency of smaller capacitor but the gain is modest. OTOH close to resonant peak we will have substantially higher impedance. For me it does not look like good deal. In fact, when low impendance at high frequences is important it looks better to connect several nominally identical capacitors. With usual tolerances they should give no parallel resonace and lower impendace due to paralleling of ESL.
In principle one could play tricks with resonance frequencies putting parallel resonace at frequency not present in circuit and serial resonances at frequencies needing suppression. But with usual tolerances of ceramics this look impractical to me.
Anyway, I wonder if I missed something and paralleling different decoupling ceramics gives some advantages? Or is this advice about paralleling just repeating old lore without understanding that world has changed?