Floorplan aspect ratio difficulties below 0.25

[cherin]

Floorplan aspect ratio

I am trying to compare the area of two circuit designs in Magma. So, I thought i would specify the same aspect ratio for both the circuits and compare the final chip area. But for one particular design. [ I had specified an aspect ratio of 0.56 and a utilization factor of 0.4 ]

It so turned out that Magma could manage only a 27% utilization for one of the circuits [Circuit A], whereas for the other one [Circuit B], it could achieve 41%.

But for circuit A, on specifying an aspect ratio of .25 and utilization of 0.4, Magma could come up with a chip of utilization of 40%.

(Q no.1) But wouldn't it be practically difficult to fabricate a chip with an aspect ratio as low as .25? Is there any generally accepted guidelines-- ie, a range of aspect ratios that are considered okay?

(Q no.2) Is there any similar guidelines for an 'acceptable utilization factor'? Is 40% too low?

 

[cherin]

Re: Floorplan aspect ratio

Well, I messed up the question with a lot of unnecessary details! Let me put it in a simple way

1) I am sure that an aspect ratio of 0.1 is too low! but i guess 0.5 is alright. So is there any lower limit for the aspect ratio which is acceptable?

2) A utilization of 100% is ideal. But there is no space for routing the wires. But if i select 40% , would it be too low?

 

[arjun1110]

Re: Floorplan aspect ratio

Hi Cherin,

2) A utilization of 100% is ideal. But there is no space for routing the wires. But if i select 40% , would it be too low?

If it is 40% at floorplan stage then it is very less.
Start floorplan with utilization of 65% to 70 % by the time you complete routing utilization might have gone upto 90%.

Regards