Derived Geometry

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In mos_pcell.il, derived geometry variables are computed before any layout objects are created. This stage converts abstract PCell parameters into concrete dimensions that will be reused consistently throughout the layout generation.

Gate Pitch

(gatePitch (+ l polySpace (* 2 gateExt)))

This expression defines the center-to-center spacing between adjacent poly gates. The inclusion of gateExt ensures that poly extends beyond active diffusion symmetrically on both sides.

Active Length

(activeLen
  (+ (* nf l)
     (* (max 0 (- nf 1)) polySpace)
     (* 2 gateExt)))

For multi-finger devices, the active length scales linearly with the number of fingers. The (max 0 (- nf 1)) term automatically suppresses poly spacing when nf = 1.

Diffusion Dimensions

(odLen (+ activeLen (* 2 sdExt)))
(odWid w)

The final OD rectangle fully encloses the active region and source/drain extensions. All downstream shapes reference these values.