MOSFET Cross-Section & I-V Curves (2D)

Bias Voltages

Gate-source V_GS 2.50 V

Drain-source V_DS 2.00 V

Device Parameters

Threshold V_th 1.00 V

Process gain k = k'_n(W/L) 2.00 mA/V²

Channel-length modulation λ 0.020 /V

Live Readout

Region

saturation

Drain current I_D

0.00 mA

Overdrive V_ov

0.00 V

Transconductance g_m

0.00 mA/V

How it works

N-channel MOSFET, long-channel (Level-1 / Shichman-Hodges) square-law model. With overdrive V_ov = V_GS − V_th:

V_GS ≤ V_th          → cutoff,     I_D = 0
V_DS < V_ov          → triode,    I_D = k·(V_ov·V_DS − V_DS²/2)
V_DS ≥ V_ov          → saturation,I_D = ½·k·V_ov²·(1+λ·V_DS)

The channel picture uses the same gradual-channel approximation the equations come from: along the channel the local potential is V(x) ≈ V_DS·x (0 at the source, x∈[0,1] toward the drain), and the inversion-layer (mobile electron) charge is proportional to V_ov − V(x). Where that would go negative the channel has pinched off — no mobile charge — which is exactly the boundary V(x) = V_ov that defines the triode/saturation split above. The channel therefore visibly widens with V_GS and pinches off short of the drain once V_DS ≥ V_ov.

The drain-body junction is reverse-biased by V_DS, so its depletion halo is drawn with the standard step-junction width law W ∝ √(V_bi + V_DS) (V_bi ≈ 0.7 V built-in potential) — it swells as V_DS rises, independent of the channel/gate physics.

Transfer curve — I_D vs V_GS at the current V_DS; the marker tracks the live operating point.
Output curves — I_D vs V_DS for several V_GS values; the dashed parabola I_D = k·V_DS²/2 is the triode/saturation boundary (V_DS = V_ov).
g_m — transconductance, computed analytically from the same equations (k·V_DS in triode, k·V_ov(1+λV_DS) in saturation).