The body effect in a MOSFET is a modification introduced to the threshold voltage to account for a gate voltage relative to the source electrode and not the device's substrate. In this situation, the substrate acts as a back gate, tuning the threshold voltage according to the MOSFET body effect equation:
VT = VT0 + γ(√(2ϕF + Vsb) - √(2ϕF))
where:
VT0 – Threshold voltage relative to the substrate;
γ – Body effect constant;
ϕF – Surface potential for inversion; and
Vsb – Source-body voltage.
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