Hi, I have a question regarding the sky130 xschem ...
# analog-designe
Enno
09/09/2023, 10:00 AMHi, I have a question regarding the sky130 xschem library. There are two different kind of of transistors. There are the normal ones and the ones with an extra symbol? Which is taking W as a total parameter for the transistor and which is taking it as finger specific width?
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Mitch Bailey
09/09/2023, 11:45 AMCan you be more specific? What do you mean by extra symbol?
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Amro Tork
09/09/2023, 12:54 PM@Enno Screenshot would be helpful.
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Enno
09/09/2023, 12:55 PMmessage has been deleted
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Amro Tork
09/09/2023, 12:55 PMThat's an LVT device.
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Enno
09/09/2023, 12:55 PMI mean the little symbol with the W
Enno
09/09/2023, 12:56 PMWhile this one hasnt got this little symbol
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Amro Tork
09/09/2023, 12:56 PMAh, I see
Amro Tork
09/09/2023, 12:56 PMI don't know to be honest.
Amro Tork
09/09/2023, 12:57 PMCould you create a netlist with both transistors and tell me which is which?
Amro Tork
09/09/2023, 12:57 PMAnd we could take a look at the netlist?
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Enno
09/09/2023, 12:59 PMmessage has been deleted
Enno
09/09/2023, 12:59 PMM34 is the one with this little symbol...
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Amro Tork
09/09/2023, 1:00 PMI don't see any difference in the equations. But I recommend that you use the one without the symbol.
Amro Tork
09/09/2023, 1:01 PMAs W in the other one is an equation.
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Enno
09/09/2023, 1:01 PMThe question still remains... Is W the finger length or the combined finger length? (for the normal one)
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Mitch Bailey
09/09/2023, 1:19 PMW is the combined effective width and not the length of a finger. On your sample schematic, if you changed nf=2 and mult=3, it might be helpful to see how the parameters are processed.
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s
Stefan Schippers
09/10/2023, 2:18 PM@Enno the symbols with the 'W' as you said are versions that take the W parameter as the single finger width. The total width of the transistor s thus calculated by xschem as Wtot = W * nf
Stefan Schippers
09/10/2023, 2:19 PMThe other transistors (without the 'W') take the W parameter as the total width. So the Finger width is calculated by xschem as:
Wfing = W / nf
Stefan Schippers
09/10/2023, 2:28 PMThe set of transistors taking W as the finger width instead as the total width were requested by some users. The drawing in the lower left corner (under the gate terminal) will hopefully visually help do distinguish these transistors.
There are no difference in simulation, these transistors use the same spice models, the only difference is how the total width is given.
My recommendation is to avoid using these transistors unless absolutely necessary, and if you absolutely need them to avoid mixing the two types (total W given or Finger W given) in the same design.
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