decap电容的数量根据什么添加啊？

typhoon222

decap电容的数量根据什么要求添加啊？

acging

如果是电源到地的，数量无所谓。

斩海之歌

版图用来补密度 数量应该无所谓吧……

typhoon222

   

acging 发表于 2021-9-22 16:27
如果是电源到地的，数量无所谓。

这样的？

typhoon222

   

斩海之歌 发表于 2021-9-22 16:33
版图用来补密度 数量应该无所谓吧……

只是补金属密度么？不是可以稳定电压，降低过充么。

fxty

其实数量不重要，太多反而会增加leakage功耗。加对位置很重要，在动态压降比较大的cell附近需要上下左右多放一些decap，一定要靠近放，太远没有意义。

demonhunter

这是个很神奇的问题，越大杂波越小，但片内面积不允许。有时候仿真看似够了，但实际出来还不够。

ericking0

大致估计一下动态电流会拉多少电荷，能接受的瞬态纹波有多大；
就可以粗略的算出来decouple电容了；

bmwbmw

如果非要说数量根据什么添加，那你就把模块旁边电源和地接进来之前的空白地方都填上电容就行了。decap电容加在模块电源地接进来之前，如果模块后就没用了。数量上通常是多多益善，当然太多也没必要。

HeshamAhmed

The decap capacitor plays a major rule in the supply behavior in some cases:
- one is when a large current step is withdrawn from the LDO, naturally the LDO will take some time depending on its GBW to respond to this current step so if you have no decap at all the voltage of the LDO will fall down to 0 before the LDO starts working, if you have a decap it will be discharged by I/C for a delta T proportional to the GBW of your LDO so if you don't want your supply to fall down when such a behavior occur you need to determine the size of a decap to give you reasonable drop.
- another is when you have high speed circuits, their activity will cause supply ripples so you need enough decaps to short the supply and gnd of these circuits at the working frequency to keep their vdd-gnd fixed.