Constant 2 of Source Follower Transfer Function Calculator

Constant B Formula:

\[ b = \frac{(C_{gs} + C_{gd}) \cdot C_t + (C_{gs} + C_{gs})}{g_m \cdot R_L + 1} \cdot R_{sig} \cdot R_L \]

Gate to Source Capacitance (C_gs):

Gate to Drain Capacitance (C_gd):

Capacitance (C_t):

Transconductance (g_m):

Load Resistance (R_L):

Signal Resistance (R_sig):

Constant B:

1. What is Constant B of Source Follower Transfer Function?

Definition: Constant B is a parameter in the transfer function of a source follower circuit that characterizes the frequency response.

Purpose: It helps in analyzing and designing MOSFET-based source follower circuits, particularly in determining their high-frequency behavior.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ b = \frac{(C_{gs} + C_{gd}) \cdot C_t + (C_{gs} + C_{gs})}{g_m \cdot R_L + 1} \cdot R_{sig} \cdot R_L \]

Where:

\( b \) — Constant B
\( C_{gs} \) — Gate to Source Capacitance (F)
\( C_{gd} \) — Gate to Drain Capacitance (F)
\( C_t \) — Total Capacitance (F)
\( g_m \) — Transconductance (S)
\( R_L \) — Load Resistance (Ω)
\( R_{sig} \) — Signal Resistance (Ω)

Explanation: The formula combines the capacitive and resistive elements of the circuit with the transistor's transconductance to determine this important constant.

3. Importance of Constant B

Details: Constant B affects the poles and zeros of the transfer function, which determine the frequency response and stability of the source follower circuit.

4. Using the Calculator

Tips: Enter all parameters with their appropriate units. Default values are provided for typical MOSFET parameters. All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical range for C_gs and C_gd?
A: For small-signal MOSFETs, C_gs typically ranges from 1pF to 10pF, while C_gd is usually smaller (0.5pF to 5pF).

Q2: How does transconductance affect Constant B?
A: Higher transconductance (g_m) reduces the value of Constant B, as it appears in the denominator.

Q3: What if my circuit has additional capacitances?
A: They should be included in the C_t (total capacitance) parameter.

Q4: How accurate is this calculation?
A: The calculation assumes ideal conditions. Actual circuits may vary by ±5% or more due to manufacturing tolerances.

Q5: Can I use this for JFET source followers?
A: The formula is MOSFET-specific, but similar principles apply to JFETs with appropriate parameter adjustments.