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Thread: Missing noise models in PMOS (3.3V & 5V-6V)

12 Discord messages from ℹ️ - Information/⁉️-questions/threads/missing-noise-models-in-pmos-33v-5v.md.

Category: ℹ️ - Information Parent channel: #⁉️-questions Thread ID: 1501344740350758992

Messages: 12

message-1501344740350758992

2026-05-05T22:07:59.736+00:00 — Brandon Hippe (@hipstair)

Content

I'm running Gm/Id sweeps for analog design, specifically using the 3.3V transistors (and possibly 5V/6V as well), and not getting any noise for PMOS models (onoise_total id and 1overf both return 0). This is not the case for the NMOS models. Has anyone else ran into this before?
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message-1501531544391782522

2026-05-06T10:30:17.29+00:00 — Tim 'mithro' Ansell (@mithro_)

Content

@Tim Edwards - Any ideas?
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message-1501573995613519903

2026-05-06T13:18:58.45+00:00 — Tim Edwards (@rtimothyedwards_19428)

Content

No, not really.  That's the first time I've heard of it.
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message-1501733983447416972

2026-05-06T23:54:42.522+00:00 — Tim 'mithro' Ansell (@mithro_)

Content

@Tim Edwards - Any idea of other people who might have done stuff using the noise models?
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message-1501738345145962576

2026-05-07T00:12:02.432+00:00 — Tim Edwards (@rtimothyedwards_19428)

Content

We did essentially zero analog stuff for the two MPW runs at Efabless.  The one thing I can think of is the last Chipathon, which was run on GF180MCU and had some analog projects.  For that, the best people to ask would be Mehdi Saligane, Mitch Bailey, and Peter Kinget.
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message-1501769130909503498

2026-05-07T02:14:22.33+00:00 — bailey (@bailey8889)

Content

I asked on Element.
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message-1501945679898087444

2026-05-07T13:55:54.889+00:00 — Christoph (@christoph_36502)

Content

For me it does work just fine using ngspice.
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message-1502121968621846540

2026-05-08T01:36:25.396+00:00 — namibj

Reply/reference

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Content

@Brandon Hippe if you can share a testbench of that sort with @Christoph , he can probably verify if it works for him.
Also, @Christoph might be so kind as to share a testbench + PDK revision hash + ngspice version + ngspice user/system config that "works for him".
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message-1502349320123453545

2026-05-08T16:39:50.218+00:00 — Brandon Hippe (@hipstair)

Content

Attachments

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message-1502349409482965202

2026-05-08T16:40:11.523+00:00 — Brandon Hippe (@hipstair)

Content

This is the spice file I'm running
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message-1503364447035719741

2026-05-11T11:53:35.334+00:00 — Christoph (@christoph_36502)

Content

Try to reduce it first to a simple simulation without all the loops. Also your save statements inside the control block should not be prefixed by "." and be stated before the simulation command.
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message-1503365064902578216

2026-05-11T11:56:02.645+00:00 — Christoph (@christoph_36502)

Content

Here is what my working control section looks like:

```
.control
save all
noise v(out,vss) vin dec 10 100 1e6 1
print inoise_total
print all
setplot noise1
gnuplot p1 inoise_spectrum
.endc
```
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