Power strips in Encounter

[kpsr]

Hi folks,
I saw one design in cadence encounter, during the power strip creations(block level) they used 2 vertical power stripes and one horizontal strip.

Why they used 2 vertical strips, please help me regarding this issue.

Thanks in advance
kpsr

 

[vimalraj205]

hai friend

Power stripes are provided for the regulated power supply through out the block or chip.
No. of stripes depends on the voltage and the current of your design. you must design the power grid that will provide equal power from alll sides of the block .

you can also use the early rail analysis method determine the IR drop in your block and lay the sufficient power stripes

you can refer this attached file and have a clear idea on power planning

this may help ypu

thank you

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hai friend

Power stripes are provided for the regulated power supply through out the block or chip.
No. of stripes depends on the voltage and the current of your design. you must design the power grid that will provide equal power from alll sides of the block .

you can also use the early rail analysis method determine the IR drop in your block and lay the sufficient power stripes

you can refer this attached file and have a clear idea on power planning

this may help you

thank you

 

[soloktanjung]

The number of power stripes is depending on the power consumption of a chip, which means different designs will have different number of power stripes. If the chip is large, therefore core power rings do not able to supply power to your standard cells because of long distance particularly the cells in the center of the chips (or will give high IR drop to the farthest cells), then you need power stripes. The number of stripes depend of the area of you chip, for e.g, for a width length of 600um, you need a vertical power stripe.

Thanks.

 

[kpsr]

Thank u hairo & vimalraj205,
They used 2 metal layers 4 and 6 as vertical.
metal 5 as horizontal.
Is there any need to use 2 metal layers as vertical.Please give the answer in detailed.

@kpsr

- - - Updated - - -

Thank u hairo & vimalraj205,
They used 2 metal layers 4 and 6 as vertical.
metal 5 as horizontal.
Is there any need to use 2 metal layers as vertical.Please give the answer in detailed.

@kpsr

 

[soloktanjung]

Now the question is more clear. I don't know what is the reason for that. I think it is sufficient to use only one metal layer for vertical and one metal layer for horizontal.

Thanks.

 

[vimalraj205]

hai frnds

the selection of your metal depends on the LEF file usually metal1 is used for the sRouting and next 3-4 are used for routing purpose for the std.cells
and usually we use higher metals for power planning since they have less resistance

and in the LEF all even Metals are Vertical routing metals and odd metals are horizontal routing metals so they prefered 4 and 6 for vertical stripes and 5 for horizontal

we can use different meatals as when we draw stripe with higher metals stacked via is placed in the sroute (metal1) and the higher metal so it may cause some shorting error or spacing error when we use that metal for routing std.cells

so to overcome this we use different metals when we use different metals reduce the width of the metals thin metal is better

I too have some doughts on this Plz correct me if i am wrong

thank you in advance

 

[praveen.kumar432]

Hi frnds
Advantage of using two power straps for vertical as well as horizontal (4, 6 layers in ur case) it reduces the congestions. it means that our rails are in metal1.If I want t to connect metal 1 to metal 6 I have to use all vias (1 to 2,2 to 3 ......5 to 6 ) use. So more space these vais are taking it may causes routing congestion. This can be avoided by using two metals.

Plz correct me if i am wrong

 

[sathyanarayana raoh]

@ praveen kumar i think wat u r telling seems correct..yes avoiding vias they migth have did like that...thumbs up praveen

 

[kpsr]

Hi praveen,
Congestion is nothing but lack of metal layers right.
Now see a design contains 6 metal layers, 3 horizontal and 3 vertical.
metal1 is not using for routing, so 2 horizontal and 3 vertical.
if we use top metal layers as power some routing resources are reduces.
congestion is increases.

please correct me if any thing wrong..

Thanks in advance
kpsr

 

[praveen.kumar432]

Hi praveen,
Congestion is nothing but lack of metal layers right.
Now see a design contains 6 metal layers, 3 horizontal and 3 vertical.
metal1 is not using for routing, so 2 horizontal and 3 vertical.
if we use top metal layers as power some routing resources are reduces.
congestion is increases.

please correct me if any thing wrong..

Thanks in advance
kpsr

Generally TOP metals only will use to power because it have less resistance.What i mean is if you use only top layers it will requires more VIAS means more area , because std cell pins are in metal 1 u have to connect from 1 to 8 (Ex see how much area you are wasting to connect power straps) to avoid what i am doing i will take 5 and 7 (V) and 6 and 8(H). If more density area i will use 5 (V)or 6(H) to connect std cells.

please correct me if any thing wrong..
Thanks
praveen