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understanding LEF and CapTbl files in a std cell library

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oAwad

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Hello all,

The following code is part of a std cell library LEF file. The resistance variable seem to be unitless "per square", so how to calculate the total resistance of a metal3 wire given its total length ?
Code: 
LAYER metal3
  TYPE ROUTING ;
  SPACINGTABLE 
    PARALLELRUNLENGTH    0.0000     0.3000     0.9000     1.8000     2.7000     4.0000     
      WIDTH 0.0000       0.0700     0.0700     0.0700     0.0700     0.0700     0.0700     
      WIDTH 0.0900       0.0700     0.0900     0.0900     0.0900     0.0900     0.0900     
      WIDTH 0.2700       0.0700     0.0900     0.2700     0.2700     0.2700     0.2700     
      WIDTH 0.5000       0.0700     0.0900     0.2700     0.5000     0.5000     0.5000     
      WIDTH 0.9000       0.0700     0.0900     0.2700     0.5000     0.9000     0.9000     
      WIDTH 1.5000       0.0700     0.0900     0.2700     0.5000     0.9000     1.5000      ;
  WIDTH 0.07 ;
  PITCH 0.14 ;
  DIRECTION HORIZONTAL ;
  OFFSET 0.095 0.07 ;
  RESISTANCE RPERSQ 0.25 ;
  THICKNESS 0.14 ;
  HEIGHT 0.88 ;
  CAPACITANCE CPERSQDIST 2.7745e-05 ;
  EDGECAPACITANCE 2.5157e-05 ;
END metal3

When getting the coupling capacitance "CC" between two metal3 wires, should I add the fringe capacitance ? or should I add it only when getting "Carea" ?

The following is part of the capTbl:
Code: 
M3
width(um)  space(um) Ctot(Ff/um)  Cc(Ff/um)    Carea(Ff/um) Cfrg(Ff/um)
0.070       0.070       0.1630       0.0565       0.0258       0.0121


Thanks
 

First thing to understand is that LEFs/captables are often too simplistic for any real capacitance to be calculated. QRC files are used for that purpose.

The unit for the resistance is given in the header of the file. If not, I believe the default is ohm.

I believe Ctot = 2*Cc + 2*Cfrg + Carea
 

ThisIsNotSam said:
First thing to understand is that LEFs/captables are often too simplistic for any real capacitance to be calculated. QRC files are used for that purpose.

The unit for the resistance is given in the header of the file. If not, I believe the default is ohm.
Click to expand...

I just want a rough estimation nothing more. So the total resistance = 0.25 * length_of_wire/wire_width ?

ThisIsNotSam said:
I believe Ctot = 2*Cc + 2*Cfrg + Carea
Click to expand...
Yeah, thanks. This makes sense.
 

oAwad said:
I just want a rough estimation nothing more. So the total resistance = 0.25 * length_of_wire/wire_width ?
Click to expand...

Yes, the answer should be in Ohms.

RPERSQ is not unitless, the units should be Ohm/square.
 

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