"MOSFET Calculator: Analyze and Optimize Your MOSFET Circuit Design

"MOSFET Calculator" is a useful tool for both electronics engineers and students alike. This calculator is designed to help in analyzing the operating conditions of a Metal Oxide Semiconductor Field-Effect Transistor (MOSFET), a common type of transistor used in digital and analog circuits. The calculations are based on the standard equations that define the operation of a MOSFET in different regions.

Here is the description, usage, and details about the parameters in the MOSFET calculator:

  1. Threshold Voltage (VT) [V]: This parameter represents the gate-source voltage (Vgs) below which the MOSFET is turned off, or more specifically, the minimum voltage required for a MOSFET to conduct. It's essential to know this parameter when you want to design a circuit in which the MOSFET should turn on at a particular voltage. The threshold voltage is generally given in volts (V).

  2. K Parameter [V⁻¹Ω⁻¹]: This is a transconductance parameter and is a measure of the MOSFET's amplification factor. It depends on the physical properties of the device, such as oxide thickness, channel width, and channel length. A higher K value means the MOSFET will have a larger drain current for a given gate voltage.

  3. Drain-source Voltage (Vds) [V]: This is the voltage applied across the drain and the source of the MOSFET. Vds affects the operation of the MOSFET by determining the region in which the MOSFET operates (cut-off, triode, or saturation).

  4. Gate-source Voltage (Vgs) [V]: This is the voltage applied between the gate and the source. Vgs controls the electric field in the channel and thus, the drain current. By adjusting Vgs, you can control the operation of the MOSFET.

  5. Length (L) [μm]: This parameter is the length of the MOSFET's channel. L is one of the critical dimensions of the MOSFET, affecting its transconductance and threshold voltage. It's usually given in micrometers (μm).

  6. Width (W) [μm]: This parameter represents the width of the MOSFET's channel. The larger the width, the more current the MOSFET can conduct. It is also typically given in micrometers (μm).

  7. Capacitance per Unit Area [F/cm²]: This parameter is the capacitance of the gate oxide per unit area. It influences the charge storage, response time, and the power consumption of the device.

  8. Electron Mobility (µN) [cm²/V.s]: Electron mobility is a measure of how easily an electron can move through the semiconductor material when an electric field is applied. The higher the electron mobility, the faster the MOSFET can switch on and off. Electron mobility is usually measured in square centimeters per volt-second (cm²/V.s).

The operation of a MOSFET can be described using a few key equations, which are the basis for calculations in the MOSFET calculator.

  1. The threshold voltage equation: This is used to determine the minimum gate-to-source voltage (Vgs) that is required to create a conducting path between the drain and the source.

    The threshold voltage (Vt) is given by:

    Vt = Vt0 + γ (sqrt(|2Φf + Vsb|) - sqrt(2Φf))

    Where: Vt0 is the threshold voltage at zero bias, γ is the body effect parameter, Φf is the Fermi potential, Vsb is the source-to-body voltage.

  2. The transconductance equation (K Parameter): The transconductance equation provides a value for the drain current (Id) under different conditions of operation.

    For the triode region (Vgs > Vt and Vds < Vgs - Vt):

    Id = K [(Vgs - Vt) * Vds - 0.5 * Vds^2]

    And for the saturation region (Vgs > Vt and Vds ≥ Vgs - Vt):

    Id = 0.5 * K * (Vgs - Vt)^2

    Where: K = μNCox(W/L) with units of A/V^2

    μN is the electron mobility, Cox is the gate oxide capacitance per unit area, W is the width of the MOSFET's channel, and L is the length of the channel.

  3. The drain-to-source current equation: This equation describes how the current through the transistor (Id) varies with the applied voltages. It's different for the different operating regions of the MOSFET (cutoff, triode, and saturation).

    For the cutoff region (Vgs ≤ Vt):

    Id = 0

    For the triode region (Vgs > Vt and Vds < Vgs - Vt):

    Id = μN * Cox * (W/L) * [(Vgs - Vt) * Vds - 0.5 * Vds^2]

    For the saturation region (Vgs > Vt and Vds ≥ Vgs - Vt):

    Id = 0.5 * μN * Cox * (W/L) * (Vgs - Vt)^2

These equations are used in the MOSFET calculator to evaluate the operation of the MOSFET under various conditions and to plot characteristics such as the transfer characteristic and the output characteristic. Understanding these equations is crucial for analyzing and designing circuits involving MOSFETs.

The MOSFET calculator uses these parameters to compute different operating points, such as the cut-off, triode, and saturation regions. It can also be used to plot I-V characteristics and analyze the influence of different parameters on the transistor's operation. In many ways, it's a powerful tool to assist in the understanding and design of circuits involving MOSFETs.


It is believed that these calculations are accurate, but not guaranteed. Use at your own risk!