🔬 MOSFET Threshold Voltage Calculator
Enter the zero-bias threshold voltage, body effect coefficient, and source-body voltage to find the actual MOSFET threshold voltage.
What This Calculator Does
A MOSFET’s threshold voltage — the gate voltage needed to turn the channel on — shifts when there’s a voltage between the source and the body (substrate) terminal, a phenomenon called the body effect. This calculator finds the actual threshold voltage under body bias from the transistor’s zero-bias threshold and body effect parameters.
The Formula
The body-effect threshold equation is Vth = Vth0 + γ × (√(2φF + VSB) − √(2φF)), where Vth0 is the threshold voltage with the source tied to the body (zero bias), γ is the body effect coefficient (a process-dependent constant, typically 0.2–0.6 √V), 2φF is the surface (Fermi) potential term of the process (commonly 0.6–0.8V), and VSB is the source-to-body voltage.
- Body effect raises the threshold voltage as VSB increases, which matters in stacked transistor circuits where the source isn’t grounded.
- γ and 2φF are process parameters usually found on a transistor’s datasheet or SPICE model.
This is the standard first-order body-effect model used in analog IC design education and general planning; exact values depend on the specific fabrication process and should be confirmed against the device’s SPICE model for precision work.