I have a circuit with a voltage regulator, IC 1 and IC 2, all of which are placed next to each other. The output from the voltage regulator (~2.5V) supplies power to IC 1 and IC 2. IC 1 is an oscillator ~ 80MHz and drives IC 2 with current around 5 mA. IC 2 is a frequency divider and reduces the frequency down to ~1 MHz. IC 2 drives a capacitive load of a few pF. Two parallel bypass capacitors 0.1uF and 1nF are used here. My question is that is it okay to share bypass capacitors among the output of voltage regulator, IC 1 and IC 2?
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1\$\begingroup\$ My 'knee jerk' reaction, but I am far from expert, is NO. As well as the principle that it is a 'bad idea' (TM), those two devices will be switching at the same frequency, so they will both be demanding current at the same time, That would make supplying power, and filtering noise worse. \$\endgroup\$– gbulmerOct 7, 2015 at 20:23
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\$\begingroup\$ hottconsultants.com/techtips/decoupling.html \$\endgroup\$– Matt YoungOct 7, 2015 at 20:26
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2\$\begingroup\$ I think more experienced people will want to see your layout (of these few components) and the values of the caps involved before answering. \$\endgroup\$– FizzOct 7, 2015 at 20:42
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No, you should have one cap for each. Well, it may in fact work even with no capacitor, but if you want to be sure, just do what you have to do. The capacitor reducec radiated emissions, ensures stable voltage and provides switching current. It's very important. Of course, pay attention to layout- connect the capacitor to the ic with shortest possible trace, use planes, etc.
Having said that, i bet it will work good enough with one cap. But do prepare pads for the other one.