Presets pick the inversion corner while holding GBW (they re-bias ID).
Sets power directly, and buys gm (→ GBW).
← strong inversion (small, fast) · weak inversion (efficient, huge) →
↑ CL ⟹ ↓ GBW (same gm drives a heavier load).
Curve = all designs at the current GBW. Red lines are the Power & Area spec limits; the shaded red half-planes are violation zones. Dragging trades power↔area at fixed GBW.
Axes: GBW · Power · Area. Each red plane is a spec; the translucent red slab beyond it is the violation volume. The dot goes red inside any slab.
| Metric | Constraint | Spec limit | Current design | Margin | Status |
|---|---|---|---|---|---|
| Power | ≤ max | 150 µW | 76 µW | 2.0× | ✔ PASS |
| Area | ≤ max | 300 µm² | 119 µm² | 2.5× | ✔ PASS |
| GBW | ≥ min & feasible | 50 MHz | 100 MHz | 2.0× | ✔ PASS |
Margin = spec ÷ current (Power/Area) or current ÷ spec (GBW). ≥ 1.0× passes; fully compliant only when all three pass.
| Target | GBW (speed) | Efficiency (power) | Compactness (area) |
|---|---|---|---|
| Minimize Area | fixed — hold the spec | fixed — accept the power | ✅ optimize — strong inversion, small W |
| Lowest Power | fixed — hold the spec | ✅ optimize — high gm/ID | ❌ flexible — area balloons (large W) |
The single physical knob is inversion level (gm/ID). At a fixed GBW, turning it up for efficiency lets you drop ID (lower power) but the device must get wide (more area); turning it down shrinks area but forces more current. CL and ID set where along GBW you sit.
First-order single-stage-OTA model tuned to a 180 nm-class node (SKY130, VDD=1.8 V nominal): JD(x)=37.6·e−x/3.77 µA/µm current density, fT(x)=20 GHz·e−(x−5)/8.69, usable GBW ceiling ≈ fT/8, area counts 4 active devices at L=0.5 µm. Absolute numbers are illustrative — the shape (GBW ∝ ID·(gm/ID)/CL, Area ∝ e+gm/ID) is the physics that holds across nodes.
Part of borenw.github.io — interactive analog circuit teaching tools.