The drain current of a MOSFET in saturation is given by

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The drain current of a MOSFET in saturation is given by I_D = K (V_{G S} – V_T)² where K is a constant. The magnitude of the transconductance g_m is—

1. K (V_GS – V_T)²
  VD^S
2. 2K (V_GS – V_T)
3. I_D
  V_GS – V_DS
4. K (V_GS – V_T)²
  V_GS

Correct Option: B

Given, I_D = K (V_GS – V_T)²
Where K is constant

g_m =		∂I_D	≈	∂	K(V_GS – V_T)²
		∂V_GS		∂V_GS

or g_m = 2K (V_GS – V_T)
Hence alternative (B) is the correct choice.