Question

For operating an n-channel JFET in pinch-off region, the condition needed to be satisfied is ________.

• A. drain current becomes linearly proportional to \( V_{DS} \)
• B. \( V_P \leq V_{GS} \leq 0 \) and \( V_{DS} \geq (V_{GS} - V_P) \)
• C. \( V_{GS} \geq V_P \) and \( V_{GS} \geq V_{DS} \)
• D. JFET acts as a voltage variable resistor

Hint:

In JFETs, pinch-off condition is when \( V_{DS} \geq V_{GS} - V_P \). Know the saturation region conditions for designing amplifiers.

Answer 1

The Correct Option is B

Step 1: Understand pinch-off
In an n-channel JFET, pinch-off is the condition beyond which the drain current \( I_D \) becomes almost constant with respect to \( V_{DS} \).
Step 2: Condition for pinch-off
To operate in pinch-off:
- \( V_{GS} \) must be negative (reverse bias gate)
- The drain-source voltage \( V_{DS} \) must be high enough so that:
\[ V_{DS} \geq V_{GS} - V_P \] Where:
- \( V_P \) is the pinch-off voltage (positive in magnitude for n-channel)
- \( V_{GS} \leq 0 \)
So we need: \[ V_P \leq V_{GS} \leq 0 \text{AND} V_{DS} \geq (V_{GS} - V_P) \] Therefore, the JFET enters saturation (active) region, and current saturates. \[ \boxed{\text{Correct condition: } V_P \leq V_{GS} \leq 0 \text{ and } V_{DS} \geq (V_{GS} - V_P)} \]