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bypass capacitors on ICs

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chico

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Do i need to put bypass capacitors on from Vcc to ground on all my ICs to reduce noise?
Someone was telling me i need to do this for circuits.
Couldnt I just have 1 bypass cap instead of 1 for each IC, in theory they are all connected together.
 
A bypass capacitor needs to be as close as possible to the IC power and ground pins. The only way to acheive that is to use one for each IC. If you use a single capacitor for all IC's on your board, the inductance of the connecting power lines will cancel the effects of capacitive bypassing.
 
hi,
For fast logic IC's its advisable to bypass every IC's power pins, as close to the IC as possible , a value of 10nF thru 47nF is usually good enough.
 
It is not as simple as counting the IC's. It has to do with the complexity of the IC and the distance of the bypass from the chip. They should be located as close to the chips power pins as possible.

With simple gate logic chips you can get buy with one bypass cap for a small number of ICs.

For some chips you need one bypass cap for each power pin.

Bypass caps are cheap. Buy and use them in quantity. :D
 
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Old fashioned TTL logic ICs needed a 0.1uF ceramic capacitor near each IC.
Newer CD4xxx Cmos logic ICs need one 0.1uf ceramic capacitor for about 5 ICs but it must be near them all.
Newer 74HCxxx high-speed Cmos ICs also need a ceramic 0.1uF capacitor near each IC.
 
Clocked logic seems to be more sensitive to supply glitches than combinational logic. So be overcautious with counters, shift registers and flip flops.
 
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