I m still struggling trying to make a simple bandgap I just

Question

I m still struggling trying to make a simple bandgap I just ran into an interesting find My simulation results for sky130 fd pr pfet 01v8 lvt with l=1 w=5 m=2 are different from the same model with l=1 w=10 Shouldn t they be the same

Weston Braun · Answer

Whats that a plot of drain voltage vs something Or is this your bandgap output

Weston Braun · Answer

I believe that the models are based on collected data from test structures and might represent some variation in nominal and width as fabricated where the true sizing of the w = 10 and w=5 m=2 fets do not match

Weston Braun · Answer

based on the texts I have been reading if you need different widths you chose one width and just change the number of fingers that gives better matching between FETs

Weston Braun · Answer

also I think the 1V8 fets models are only valid for voltages up to 1 8V I see the X axis goes up to 5V so you might be running into issues with those models

Patrick Van Oosterwijck · Answer

< Weston Braun> Yeah this is the bandgap output Not very good I know but seeing things like this happen makes me think I can never get it anywhere near good To get good matching you need more than just fingers the devices need to be split into a centroid layout and maybe with opposing current flow AFAIK But that may be old info I don t know about newer processes Anyway I m nowhere near the point where I worry about layout I just want a fricking simulation to work well and I can t even get to that point so

Weston Braun · Answer

it should be possible My best guess is its just due to the difference between nominal and actual transistor sizes between the two bins impacting matching

Weston Braun · Answer

do you have your work online anywhere I am interested in what others are doing and I need a bandgap reference