MOSFET Unity-Gain Frequency Calculator

MOSFET Unity-Gain Frequency Formula:

\[ f_t = \frac{g_m}{C_{gs} + C_{gd}} \]

Transconductance in MOSFET (g_m):

Siemens

Gate Source Capacitance (C_gs):

Farad

Gate Drain Capacitance (C_gd):

Farad

Unity Gain Frequency in MOSFET (f_t):

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1. What is MOSFET Unity-Gain Frequency?

The Unity Gain Frequency (f_t) in a MOSFET refers to the frequency at which the voltage gain of the device drops to 1 (0dB) in a common-source configuration with a resistive load. It represents the maximum frequency at which the transistor can provide useful amplification.

2. How Does the Calculator Work?

The calculator uses the MOSFET Unity-Gain Frequency formula:

\[ f_t = \frac{g_m}{C_{gs} + C_{gd}} \]

Where:

\( f_t \) — Unity Gain Frequency (Hz)
\( g_m \) — Transconductance in MOSFET (Siemens)
\( C_{gs} \) — Gate Source Capacitance (Farad)
\( C_{gd} \) — Gate Drain Capacitance (Farad)

Explanation: The formula calculates the frequency at which the MOSFET's current gain becomes unity, determined by the ratio of transconductance to the sum of gate-source and gate-drain capacitances.

3. Importance of Unity-Gain Frequency

Details: Unity Gain Frequency is a critical parameter in RF and high-frequency circuit design as it indicates the maximum operating frequency of the MOSFET. Higher f_t values allow for better high-frequency performance and faster switching speeds.

4. Using the Calculator

Tips: Enter transconductance in Siemens, gate-source capacitance in Farad, and gate-drain capacitance in Farad. All values must be positive, and the sum of capacitances must be greater than zero.

5. Frequently Asked Questions (FAQ)

Q1: What is the typical range of Unity Gain Frequency in modern MOSFETs?
A: Modern MOSFETs can have f_t values ranging from several GHz to over 100 GHz, depending on the technology node and device geometry.

Q2: How does temperature affect Unity Gain Frequency?
A: Temperature increases typically reduce transconductance and may affect capacitances, generally leading to a decrease in f_t at higher temperatures.

Q3: Why is f_t important in amplifier design?
A: f_t determines the maximum frequency at which the MOSFET can provide voltage gain, making it crucial for designing high-frequency amplifiers and oscillators.

Q4: How can I increase the Unity Gain Frequency of a MOSFET?
A: Reducing gate length, minimizing parasitic capacitances, and optimizing device geometry can help increase f_t.

Q5: Is f_t the same as the maximum oscillation frequency?
A: No, f_t is the unity current gain frequency, while maximum oscillation frequency (f_max) is typically higher and represents the frequency where power gain becomes unity.