Fix: un-given device TEMP defaults to 0 °C instead of ambient $temperature#144
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Gerd-Vandersteen wants to merge 1 commit into
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Fix: un-given device TEMP defaults to 0 °C instead of ambient $temperature#144Gerd-Vandersteen wants to merge 1 commit into
Gerd-Vandersteen wants to merge 1 commit into
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…ture prepare_static_inputs special-cased tnom/tref/tr -> 27.0 but let an un-given device `temp`/`temperature` parameter fall through to the 0.0 fallback, because openvaf_py get_param_defaults() drops computed defaults like EKV's `TEMP = -`NOT_GIVEN`` (= 1e21). The model then evaluated `T = TEMP + 273.15 = 273.15 K` (0 C) instead of `T = $temperature` (the ambient, 300.15 K / 27 C), so EKV ran ~27 C too cold. Surfaced by a VACASK cross-check: EKV Id was bias-dependently off (-46% subthreshold .. +1% strong inversion). Fix: default un-given temp/temperature to the 1e21 "not given" sentinel so the model's own `if (TEMP == -`NOT_GIVEN)` branch selects $temperature. EKV_DEBUG now shows T=300.15, Vt=0.025865; EKV Id 5.32 -> 7.17 uA at Vg=0.7/Vd=1.0. Only EKV carries a TEMP param among bundled models; device_models + corners tests unaffected. Deeper fix belongs in openvaf_py get_param_defaults() (capture sentinel/computed defaults). NB: this unmasks a separate, residual MIR-eval-vs-OSDI EKV difference (VP/if_/KP_Weff, +20%->-7% across bias) that the temperature error was partially cancelling.
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Companion PR: #145 fixes the nominal temperature ( |
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Problem
When a device does not specify
TEMP, VAJAX passes the parameter to the compiled model as0.0— read by the model as "0 °C was given" — instead of the Verilog-A "not given" sentinel-\NOT_GIVEN(= +1e21for models using ``define NOT_GIVEN -1.0e21``). The model thereforetakes
T = TEMP + 273.15 = 273.15 K(0 °C) rather than falling back to the ambient`$temperature`. Every device silently runs 27 °C too cold.
Root cause: in
prepare_static_inputs(vajax/analysis/openvaf_models.py), un-giventnom/tref/trwere special-cased but un-given
temp/temperaturefell through to the generic0.0fallback(
get_param_defaults()drops computed/sentinel defaults like-\NOT_GIVEN`, so nothing suppliedthe right value).
Fix
Default un-given
temp/temperatureto the-\NOT_GIVENsentinel (1e21) so the model's own "not given →$temperature`" branch runs.Evidence
On EKV at
Vg=0.7, Vd=1.0: the device now reportsT=300.15 K,Vt=0.025865, andIdmoves5.32 → 7.17 µA— matching an independent VACASK/OSDI run of the same.vaat the ambient.Note
A deeper alternative would be to teach the openvaf_py
get_param_defaults()extraction to emitcomputed/sentinel defaults (so the runtime fallback need not special-case temperature names). This
PR is the minimal, targeted runtime fix. A companion PR fixes the nominal temperature (
TNOM).