Decoupling capacitor for power supply ?

[taofeng]

What kind of mos capacitor is more area efficient ? N-type , P-type or MIM capacitor ?

Which one is better in terms of the suppression of power supply noise given the same capacitance value ? and Why ?


regards,

 

[Teddy]

MOS caps are more area efficient - you should be able to calculate it quite easy.
MIM is better for noise - does not inject any noise to substrate.

 

[freelancer]

For decoupling capacitors for power supply,what it needs is the large capacitance to reject the power supply fluctuation,the capacitor behaves like a reservoir,the larger the capacitance ,the better rejecting effect.so the MOS capacitor is prefered for its large capacitance with little area.
the MIM capacitor is more used in Analog and RF circuits for its precise capacitance value and better matching characteristic,not usually used with large values for the reson of area and process problem.
when came to the problem of which MOS capacitor is better,NMOS or PMOS.we must consider it in different process,singe N-well or twin-well or triple-well,the selection is differed among these different process,with the consideration of isolation,nosie influence,etc.

 

[ukint]

Basically MOS capacitors are better. NMOS caps are preferred over PMOS caps due to the presence of large intrinsic capacitance for NWELL when compared to PWELL. Hope this helps!

Regards,
Vivek

 

[milkdragon]

MOS device is more area efficient. However, i typically use the combination of MOS and MIM as MIM cap is more efficient to filter high frequency noise

 

[yashiro]

how do you calculate the capacitance of the MOS cap?

 

[milkdragon]

Since it is used as bypass, the device is in triode region and can be approximated by
W*L*Cox/2+W*Co
where W is the width of the device, L is the gate length Cox is the oxide capacitance, Co is the overlap capacitance between gate and drain/source area

 

[boba]

But remember that the noise will inject so if there is likely to be much put taps close by.

 

[spring1860]

For decoupling capacitors for power supply,what it needs is the large capacitance to reject the power supply fluctuation,the capacitor behaves like a reservoir,the larger the capacitance ,the better rejecting effect.so the MOS capacitor is prefered for its large capacitance with little area.
the MIM capacitor is more used in Analog and RF circuits for its precise capacitance value and better matching characteristic,not usually used with large values for the reson of area and process problem.
when came to the problem of which MOS capacitor is better,NMOS or PMOS.we must consider it in different process,singe N-well or twin-well or triple-well,the selection is differed among these different process,with the consideration of isolation,nosie influence,etc.

lesson learned thank u

 

[sunny153]

mos cap is beeter for decoupling cap