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Why do we need to close timing with different voltage ?

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rahul.achates

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HI

During STA, we run it for PVT , mean closing timing with different temperature, voltage and process , even for a chip, voltage supply will not be changed. Then we do we have to closing timing with different voltage ? Is it having some relationship with real time ?

Rahul J
 

Hi Rahul,
At present technology, for example consider same cell is utilised twice/thrice in your design. then the behaviour of this cell will not be same. so we check the timing for the complete design use different corners (PVTs). There might be some paths which would be clean in timing wrto chosen fast and slow corner, but fails in other corners.

Sasi
 

Setup and hold times margins are not always predictable. SSTA is preferred over STA in complex systems.

3σ slacks obtained with SSTA are generally larger than the corresponding STA slacks.
 

Hi Rahul,

as per my understanding if we are making one product then it might be operated in different condition so we check in worst normal(typical) and best case. Suppose you have a design that can operate normal at 1.8v but some of your component will become shutdown only when supply is below 1.6 and for some condition you need 1.9v so you have to test your chip for different condition and on different voltages temp will be different so we name these conditions as PVT condition and also characterize our libraries for these conditions. So that we can check timing on these corners.
 

Thanks guys for the effort.

Think about your smart phone, voltage supply will not be same when your battery level is 100% and 10% , so basically your cellphone will be having somewhere 3.6v (10% battery ,2000mah ) to 4v (100%, 2000mah).

Your device should work properly with in that range , I think that's why we need to close timing with different voltage.

Same will apply with temperature, device may go to south africa or may operate from Kashmir ... it should work.

Rahul J
 
Nice example rahul :) yeah that's why we check.
 

correct me if I'm wrong, but I believe the smartphone voltage will not change regardless of battery level. Especially for the digital circuits part. Voltage change from 0.9 to 1.1V is considered very big(over 20% change).
Setup and hold timing check must pass in all PVT corners, if possible. Usually if setup pass in ss and hold passes in ff corner, the design should be fine.

rahul.achates said:
Thanks guys for the effort.

Think about your smart phone, voltage supply will not be same when your battery level is 100% and 10% , so basically your cellphone will be having somewhere 3.6v (10% battery ,2000mah ) to 4v (100%, 2000mah).

Your device should work properly with in that range , I think that's why we need to close timing with different voltage.

Same will apply with temperature, device may go to south africa or may operate from Kashmir ... it should work.

Rahul J
Click to expand...
 

you can check your cellphone , I have one application which is to save battery , called "battery doctor" , this app will show the voltage level also and I saw many time it's level to 4v when fully charge and 3.7v when it is 10% ..

You can think about the battery, whatever inside battery have, if you use it then it will be weak as you go ... it is not like throughout 100% to 0% , battery deliver same power and then it one just cut off ...
 
Hi Rahul

To my understanding, there should be a power regulator(or level shifter) between battery output and the chip digital/analog power domain on smartphone.
With the regulator, the digital voltage is separated from the direct battery power output.
It does not make sense to me that the 4.0/3.7V power is directly driving the digital circuit, as nowadays chips are produced under 28-20ns(or lower) technology, which demands a much smaller functional voltage swing to achieve fast signal transition from 1 to 0 or vice versa. 4.0/3.7V input power would not work for digital processor chips.

Please let me know if you have some more interesting findings in term of powering a smartphone.

Regards

rahul.achates said:
you can check your cellphone , I have one application which is to save battery , called "battery doctor" , this app will show the voltage level also and I saw many time it's level to 4v when fully charge and 3.7v when it is 10% ..

You can think about the battery, whatever inside battery have, if you use it then it will be weak as you go ... it is not like throughout 100% to 0% , battery deliver same power and then it one just cut off ...
Click to expand...
 

Hi Rahul

I think closing timing under different voltage has something to do with the IR drop in the chip.
As we know, the acctual voltage level on leaf cell in chip will have some swing (may be larger or smaller), comparing with the voltage applying to the power bump. coz, there will be some IR drop brought by the complex power grid.
So, when we run the power analysis, we should guarantee the IR drop will not reach a specified limit.
That is just my understanding. If somebody has some comments, plz correct it.
Thanks!
 

HI Owen ..

May be you are correct , I will ask this to PD team they might be knowing. Will update it once I have solid answer.
 
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