MOSFET Calculator
Free calculate drain current, transconductance, and mosfet parameters. Get instant, accurate results with our easy-to-use calculator.
Input Parameters
K = ½μC_ox(W/L), process-dependent
Results
Enter parameters to calculate
What is a MOSFET?
A MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is a type of transistor used for switching and amplifying electronic signals. It's controlled by voltage applied to the gate terminal, making it a voltage-controlled device.
MOSFETs operate in three regions: cutoff (V_GS < V_th, no current), linear/triode (V_GS > V_th, V_DS < V_GS - V_th, current varies with V_DS), and saturation (V_GS > V_th, V_DS > V_GS - V_th, current constant with V_DS).
MOSFETs are fundamental in digital circuits (CMOS logic), power electronics, and analog circuits. They're the building blocks of modern microprocessors and integrated circuits.
MOSFET Formulas
Saturation Region
When V_DS > V_GS - V_th
Linear Region
When V_DS < V_GS - V_th
Transconductance: g_m = 2K(V_GS - V_th) in saturation, g_m = 2KV_DS in linear
How to Calculate
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1
Determine operating region
Check if V_DS > V_GS - V_th (saturation) or V_DS < V_GS - V_th (linear).
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2
Calculate overdrive voltage
V_OV = V_GS - V_th. This is the voltage above threshold.
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3
Apply appropriate formula
Saturation: I_D = K × V_OV². Linear: I_D = K[2V_OV×V_DS - V_DS²].
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4
Calculate transconductance
g_m = 2K(V_GS - V_th) in saturation. This measures gain (change in I_D per change in V_GS).
Practical Examples
Example 1: Saturation Region
K = 0.001 A/V², V_GS = 5 V, V_th = 2 V.
Solution:
V_OV = 5 - 2 = 3 V
I_D = 0.001 × 3² = 0.001 × 9
I_D = 0.009 A = 9 mA
Applications
Digital Circuits
CMOS logic gates, microprocessors, and digital integrated circuits. MOSFETs are the foundation of modern computing.
Power Electronics
Switching power supplies, motor control, and high-power applications. Power MOSFETs handle large currents.
Analog Circuits
Amplifiers, oscillators, and signal processing. MOSFETs provide high input impedance and low power consumption.
Education
Teaching semiconductor physics, understanding transistor operation, and designing electronic circuits.
Frequently Asked Questions
What is the threshold voltage?
Threshold voltage (V_th) is the minimum gate-source voltage needed to create a conducting channel. Below V_th, the MOSFET is off (cutoff). Above V_th, current can flow.
What is the transconductance parameter K?
K = ½μC_ox(W/L), where μ is mobility, C_ox is oxide capacitance, W is channel width, L is channel length. It's process-dependent and determines current capability.
What's the difference between NMOS and PMOS?
NMOS uses n-channel (electrons), turns on with positive V_GS. PMOS uses p-channel (holes), turns on with negative V_GS. CMOS uses both (complementary).
What is body effect?
Body effect increases threshold voltage when source is not at substrate potential. V_th increases with |V_SB|. This affects circuit behavior in non-ideal conditions.
How does channel length affect performance?
Shorter channels (smaller L) increase K and current, but also increase leakage and reduce control. Modern processes use very short channels (nanometers) for speed, but require special techniques to control leakage.