MOSFET Calculator

Metal-Oxide-Semiconductor Field-Effect Transistors operate across distinct physical regions determined by terminal voltages. In the Cut-Off Region, the gate-source voltage ($V_{GS}$) remains below the threshold voltage ($V_{th}$), resulting in zero drain current. In the Triode (Linear) Region, where $V_{DS} < V_{GS} - V_{th}$, the transistor acts like a voltage-controlled resistor using the equation: $I_{triode} = 2 \cdot K_{Mos} \cdot V_{DS} \cdot (V_{GS} - V_{th} - 0.5 \cdot V_{DS})$. In the Saturation Region, where $V_{DS} \ge V_{GS} - V_{th}$, the channel pinches off, and the drain current becomes independent of drain-source voltage, modeled by: $I_{saturation} = K_{Mos} \cdot (V_{GS} - V_{th})^2$. The process constant $K_{Mos}$ integrates physical properties including electron mobility, oxide capacitance, and the channel's width-to-length ratio.

Consider a MOSFET circuit where the process transconductance parameter $K_{Mos}$ is $0.5 \text{ mA/V}^2$, the gate-source voltage ($V_{GS}$) is $5\text{ V}$, the threshold voltage ($V_{th}$) is $1.5\text{ V}$, and the drain-source voltage ($V_{DS}$) is $3\text{ V}$. First, verify the operating region by checking the condition: $V_{DS}$ ($3\text{ V}$) is greater than $V_{GS} - V_{th}$ ($5 - 1.5 = 3.5\text{ V}$)? Since $3 < 3.5$, the device operates in the triode region. Applying the triode equation: $I_{triode} = 2 \cdot 0.5 \cdot 3 \cdot (5 - 1.5 - 0.5 \cdot 3) = 3 \cdot (3.5 - 1.5) = 3 \cdot 2 = 6\text{ mA}$. Thus, the resulting drain current is $6\text{ mA}$.

Always verify your threshold voltage ($V_{th}$) specifications against manufacturer datasheets, as temperature variations can significantly shift this value. Double-check your unit conversions—especially when switching between micrometers for channel dimensions and milliamperes for currents—to prevent massive scale errors. Finally, always evaluate your $V_{DS}$ versus $V_{GS} - V_{th}$ boundaries first before applying triode or saturation formulas to avoid calculating using the wrong physical model.