< U017UPJEGKZ> changing W and L now must be done with care a open-source-silicon.dev #analog-design

<@U017UPJEGKZ> changing W and L now must be done w...

Stefan Schippers

10/13/2020, 2:05 AM

@User changing W and L now must be done with care as only a discrete set of W/L are available. I hope in the future this limitation will be removed at least to some W - L intervals

Patrick Van Oosterwijck

10/13/2020, 3:40 AM

Are you saying the bins aren't really bins but only certain W/L combos that are available? 🤯 What happens if you don't choose those?

Stefan Schippers

10/13/2020, 9:01 AM

@Patrick Van Oosterwijck taking for example the nfet_01v8 the file cells/nfet_01v8/sky130_fd_pr__nfet_01v8.pm3.spice that gets included has only a discrete set of geometrical points, if you grep the lengths 0f 0.5um you get:

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+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 9.95e-07 wmax = 1.005e-6
+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 2.995e-06 wmax = 3.005e-6
+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 4.995e-06 wmax = 5.005e-6
+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 6.995e-06 wmax = 7.005e-6
+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 4.15e-07 wmax = 4.25e-7
+ lmin = 4.95e-07 lmax = 5.05e-07 wmin = 5.45e-07 wmax = 5.55e-7
+ lmin = 4.99e-07 lmax = 5.01e-07 wmin = 6.49e-07 wmax = 6.51e-7

so you can use only w=0.42um, 0.55um, 0.64um, 1um, 3um, 5um, 7um

Stefan Schippers

10/13/2020, 9:09 AM

However i noted that in addition to

sky130_fd_pr__nfet_01v8.pm3.spice

there is also a

sky130_fd_pr__nfet_01v8__tt.pm3.spice

(that is not used by the top lib file) that contains continuous regions for w and l. I don't know however if the models are behaving well ouside these 'fixed' w/l combinations:

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+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 7.0e-06 wmax = 0.0001
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 7.0e-06 wmax = 0.0001
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 5.0e-06 wmax = 7.0e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 5.0e-06 wmax = 7.0e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 3.0e-06 wmax = 5.0e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 3.0e-06 wmax = 5.0e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 2.0e-06 wmax = 3.0e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 2.0e-06 wmax = 3.0e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 1.68e-06 wmax = 2.0e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 1.68e-06 wmax = 2.0e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 1.26e-06 wmax = 1.68e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 1.26e-06 wmax = 1.68e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 1.0e-06 wmax = 1.26e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 1.0e-06 wmax = 1.26e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 8.4e-07 wmax = 1.0e-6
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 8.4e-07 wmax = 1.0e-6
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 7.4e-07 wmax = 8.4e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 7.4e-07 wmax = 8.4e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 6.5e-07 wmax = 7.4e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 6.5e-07 wmax = 7.4e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 6.4e-07 wmax = 6.5e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 6.4e-07 wmax = 6.5e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 6.1e-07 wmax = 6.4e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 6.1e-07 wmax = 6.4e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 6.0e-07 wmax = 6.1e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 6.0e-07 wmax = 6.1e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 5.8e-07 wmax = 6.0e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 5.8e-07 wmax = 6.0e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 5.5e-07 wmax = 5.8e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 5.5e-07 wmax = 5.8e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 5.4e-07 wmax = 5.5e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 5.4e-07 wmax = 5.5e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 5.2e-07 wmax = 5.4e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 5.2e-07 wmax = 5.4e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 4.2e-07 wmax = 5.2e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 4.2e-07 wmax = 5.2e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 3.9e-07 wmax = 4.2e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 3.9e-07 wmax = 4.2e-7
+ lmin = 5.0e-07 lmax = 1.0e-06 wmin = 3.6e-07 wmax = 3.9e-7
+ lmin = 2.5e-07 lmax = 5.0e-07 wmin = 3.6e-07 wmax = 3.9e-7

if the

sky130_fd_pr__nfet_01v8__tt.corner.spice

file included by

sky130.lib.spice

top lib file is modified to include this

__tt.pm3.spice

file then all W from 0.36 to 100um can be used for a L=0.5um transistor. This is the change (in red) : sky130.lib.spice --include--> nfet_01v8/sky130_fd_pr__nfet_01v8__tt.corner.spice --include--> sky130_fd_pr__nfet_01v8`__tt`.pm3.spice

Stefan Schippers

10/13/2020, 9:17 AM

@Patrick Van Oosterwijck if you set a w/l combination that is not present in the list of available 'points' or 'regions' ngspice says 'model not found'

Patrick Van Oosterwijck

10/13/2020, 4:21 PM

Oh. Hmm, I do not get "model not found". I am using _lvt models and it seems the corner.spice already includes the pm3.spice. So I guess it's working correctly then.

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