Multiple choice

An n-channel depletion MOSFET has following two points on its ID -VGS curve: (i) VGS = 0 at ID = 12 mA and (ii) VGS = - 6 volts at ID = 0

Which of the following Q-points will give the highest trans-conductance gain for small signals?

  1. VGS = - 6 Volts

  2. VGS = - 3 Volts

  3. VGS = 0 Volts

  4. VGS = 3 Volts
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B Correct answer
Explanation

 The transconductance for the junction FET is given by gm = (2 Idss/|Vp |) [1 - (Vgs/Vp)] Vp is the pinch off voltage. Max transconductance can occur between pinch off voltage and at origin. So it lies between - 6V and 0. So Q point = - 3 V

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