Concept — Charge-Conserving Q-V Model

A large-signal model that backs out non-linear capacitance from “dynamic charge measurements” such as gate charge Q_G and output charge Q_oss, guaranteeing charge conservation.

Core Relation

$Q=\int C(v)dv$. Continuous transient integration over the switching trajectory yields $Q_G$ (total gate charge), $Q_{GS}$ (up to the Miller plateau), $Q_{GD}$ (Miller transition), $Q_{oss}$ (output charge).

Why Superior to Small-Signal AC

• Small-signal AC cannot measure the C_gd spike at low V_DS (instrumentation limit).
• Charge integration spans the entire trajectory and can back out the low-voltage peak and knee voltage.
• From charge conservation at the Miller plateau and overdrive region, key parameters such as C_gd,low and V_trans,gd can be solved.

Verification Loop

Numerically integrate Q_oss (trapezoidal rule) to back out the total charge of C_ds + C_gd, align with the datasheet’s Q_oss,spec, and fine-tune C_2DEG / V_trans until they match. See non-linear-capacitance-extraction.

Related

• non-linear-capacitance-extraction, miller-plateau
• power-semiconductor-modeling