Thank you! As for the delay cells, are they just a chain on inverters? How do they implemented?
What does it mean? Why is it done? How do this effect on the delay? Does it increase it? Is it was not enough to put just a chain of regular inverters? Why?two middle inverters have non-minimum gate length of transistors
how does this reduce IR drops?Decap is capacitance cell between the two power rings.
To reduce the IR drop, you could connect the metal filling to a power, for example odd layer to gnd and even layers to vdd.
how does this reduce IR drops?
it will add additional capacitance to power mesh. So, it will reduce the IR drop (to get IR drop you need to discharge the capacitance of the power mesh).
This additional cap (of power network) acts as local charge storage and is helpful in mitigating the voltage drop. When the cells of your design is switching, they consume the power and additional caps will give them their charge (until power supply network will be able to compensate the required power).
I can not explain in more easy way. The bigger capacitance (cap of power straps), the more difficult to discharge it (if you have the same number of your logic cells, it will be more difficult for them to discharge the bigger capacitance of power straps).
Thanks very much for your quick response, oratie.
I have ever heard that Decap cell can be used as charge pool when the nearby switching instances need charge.
But I haven't seen any document on this use of additional power segment.
Can you provide me some document or link on this topic?
In my opinion, I think It is because of the Resistence reduction on power and ground routing that be helpful to mitigatint IR drop.
when connecting the metal filler with power and ground, the resistence of power and ground routing will be reduced coz of parallel connection.
So result of I*R comes down, then the IR drop comes down.
Do you think so ?
Yes, the resistance reduction of power mesh will help in IR-drop reduction.In my opinion, I think It is because of the Resistence reduction on power and ground routing that be helpful to mitigatint IR drop.
Here is misunderstanding. There is a metal fill - it is just a pieces of metal (which can be inserted by the tool). If you connect one edge of this metal to the power/ground, it will not reduce the resistance, because the other edge still is unconnected. It will just add an additional capacitance to the power mesh. Yes, if you have enough empty area, you may place this metal fill polygon parallel to the power strap and connect both edges to the strap - in this case, the resistance will be smaller. Good to IR-drop reducing.when connecting the metal filler with power and ground, the resistence of power and ground routing will be reduced coz of parallel connection.
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