open-source-silicon.dev

New feature in xschem. Scope symbols to quickly inspect nets / device currents.
<https://www.youtube.com/watch?v=hVCIlAvAM5A>

Very nice! I‘ll need to try this :grinning: 

Could you do something similar to easily check the most important transistor parameters. Something I can attach to a device and see the properties?

<@U01819B63HP> like the ammeter scope: selecting a device, add the "op symbol" and get operating point data.

<@U02UAUGSQ22> Displaying device OP data be done but:
• data must be explicitly saved before running the simulation. Sadly there is not a save all command (at least AFAIK)  that would be very useful for many analog blocks (that not that big that saving everything becomes an issue).
• the syntax for the saved nodes is *very* simulator specific. (ngspice). But it's the most used simulator so it is worth doing anyway.
Will work on that .

<@U01819B63HP> super, that would help a lot! Constructing the op save statements is a hassle, so this is a big help to automate that away. BTW, gm, gds, Ids, Vth, fug would likely be the most important parameters for MOSFET. 

<@U02UAUGSQ22> what is the last parameter above? `fug`

image.png

1.png

<@U02UAUGSQ22> so you are referring to the unity current gain frequency, right?
[edit] Sorry it was displayed in the full picture. I didn't click the image and saw only the 3 capacitors

<@U02UAUGSQ22> BSIM4 models have a parameter for cgd (Intrinsic Source-Drain transcapacitance) and for cgdo (Gate-Drain overlap and fringing capacitance) Should take the second one (and similar cgso for source) ? Or should I take the sum?
From your formula above it seems overlap/fringe  capacitance fits best in the formula.

<@U02UAUGSQ22> I have something that seems to work, and will shortly push a commit to `xschem_sky130`.
Display device model parameters is strongly pdk dependent so each pdk should have its specific scripts to do the task.
I have done the test on sky130.
There are 2 functions.
• generating the .save lines to get all these parameters saved, this is the most boring part to do manually (due to the complex syntax):
`...`
`.save @m.x1.xm2.msky130_fd_pr__nfet_01v8_lvt[vdsat]`
`.save @m.x1.xm2.msky130_fd_pr__nfet_01v8_lvt[cgg]`
`.save @m.x1.xm2.msky130_fd_pr__nfet_01v8_lvt[cgso]`
`.save @m.x1.xm2.msky130_fd_pr__nfet_01v8_lvt[cgdo]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[gm]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[gds]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[vth]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[vdsat]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[cgg]`
`.save @m.x1.xm3.msky130_fd_pr__pfet_01v8_lvt[cgso]`
`...`
• Displaying (annotating) these values in the schematic. This is done with a new `annotate_fet_params.sym` symbol: