What's better: one big capacitor or series of smaller ones of the same value?

[road_0506]

Hello guys..
I wonder which is better, 1big capacitor or smaller capacitors of the same value as the former. What are the drawbacks of each?
Any comments would be appreciated...
Thanks...

 

[Humungus]

Re: capacitor comparison

If it is just one capacitor that you must create, then I think is equivalent. The only concern there is the access resistance. By dividing the capacitor into several smaller ones, you can improve the series resistance and then the bandwidth of the capacitor.

Smaller capacitors increase the perimeter/area ratio. Additionaly the fringing capacitances from the top terminal to the substrate, considering you want to create a floating capacitor (none of the terminals connected to GND), increase compared to the case of a single capacitor.

On the other side, if you need to match this capacitor to anotherone, for sure dividing it into several smaller capacitors is the best solution as you can implement common centroid layouts. In this case also the perimeter/area ratio of the two matched capacitors would be optimal.

 

[sengyee88]

Re: capacitor comparison

I think a big capacitor does not give any advantage, however, smaller cap in parallel does give some:
1. Smaller cap, you may not need to specifically reserve a big area for the capacitor. It can be squeezed into some empty spaces, hence giving area saving.
2. Smaller cap, earsier to match if is required.
3. For power supply filtering, a big cap gives at most 1st order filtering (neglect effect of inductor from bonding). smaller cap that scattered throughout the entire chip give higher order filtering effect.

 

[thcm]

capacitor comparison

It depends on your process and usage. In my recent design. I compared a 10pf cap and 2*5pf
cap,the former shows better performance for my
circuitry. You have mentioned the parasitic res is
the great concern---that's right. but it doesn't mean
split the bigger cap into smller parts can help it.

 

[road_0506]

Re: capacitor comparison

thank you guys for the brilliant ideas...
i appreciate it..
regards...

 

[safwatonline]

capacitor comparison

smaller cap in parallel ("with the same total value") are larger in area ,i don't see how they improve the leakage as lets say that the small cap. has a parallel resistance R then it will decrease cause all small caps in parallel giving smaller Q

the only advantage that i see from a large number of caps is that they help in matching (with other similar cap)