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Possibility to distribute capacitors after supply rails in layout

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Junus2012

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Hello

For design compactness, I found in my layout if I distribue the capacitors above VDD and below GND it will give best area optimization , but since I neve seen amplifier is layouted in this fashion I would like to ask you if it has a problem or not, please refer to the attaced image

cap.png


thank you
 

Yes, it is ok. These decoupling caps don't even have to match.
 
Thank youz Suta, but those are not the decoupling caps, they are the compensation capacitor of the amplifier!
 

The only question that comes to mind is
whether by "remoting" the comp cap, any
excess inductance might kill HF effectiveness.
For audio amp I would not expect trouble
but for RF, you might. Though RF tends to
not be closed loop, compensated type
amplifiers.

Depending on the compensation style you
might be able to put the caps above or
under the busses (Z-axis stack) rather than
outboard, in-plane. Depends on cap type
and impact of coupling. Shunt compensation
ought to be a no-brainer, Miller you'd need
to take care about signal division into the
stray capacitances.
 
dick_freebird said:
Depending on the compensation style you
might be able to put the caps above or
under the busses (Z-axis stack) rather than
outboard, in-plane. Depends on cap type
and impact of coupling. Shunt compensation
ought to be a no-brainer, Miller you'd need
to take care about signal division into the
stray capacitances.
Click to expand...

Those are the miller compensation of the amplifier

I would say that every amplifier layout I have worked or seen before, the cap are on the X-axis to the end of the chip and between the supply rails as the other circuit components. In my current design the capacitor array I have is big and I found it useful to put it above and below the supply rails,
simulation is showing me good results, but I am afraid that it is not standard way and then I may have problem during fabrication. That is my main concern indeed.
 

Junus2012 said:
Thank youz Suta, but those are not the decoupling caps, they are the compensation capacitor of the amplifier!
Click to expand...


I am sorry. I misunderstood then. Yes, they have to match. Make sure you have same connections from each half of your diff amp to the respective compensation caps.
 
sutapanaki said:
I am sorry. I misunderstood then. Yes, they have to match. Make sure you have same connections from each half of your diff amp to the respective compensation caps.
Click to expand...

So it is ok in IC design to have capacitors or big resistors are layouted after the supply rails
 

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