Question

A certain JFET has transconductance 4mS with an external AC drain resistance 1.5kΩ, what is the ideal voltage gain?

• A. \( 60 \)
• B. \( 6 \)
• C. \( 3.75 \times 10^5 \)
• D. \( 2.6 \times 10^{-6} \)

Answer 1

The Correct Option is A

The ideal voltage gain \( A_V \) of a JFET is given by the formula:

\(A_V = g_m \times R_D\)

Where:

• \( g_m \) is the transconductance of the JFET (in Siemens)
• \( R_D \) is the external AC drain resistance (in ohms)

Given:

• Transconductance \( g_m = 4 \, \text{mS} = 4 \times 10^{-3} \, \text{S} \)
• External AC drain resistance \( R_D = 1.5 \, \text{k}\Omega = 1.5 \times 10^3 \, \Omega \)

Now, substitute these values into the formula to find the voltage gain:

\(A_V = (4 \times 10^{-3}) \times (1.5 \times 10^3) = 6\)

Conclusion: The ideal voltage gain \( A_V \) is 60.