The transistors in the circuit of given below have parameter

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The transistors in the circuit of given below have parameter V_TN = 0.8 V, k_n = 40 µA/V² and λ = 0. The width-to-length ratio of M₂ is
W = 1.
L ₂

If V₀ = 0.10 V when V_i = 5 V, then
W for M₁ is:
L ₁

1. 47.5
2. 28.4
3. 40.5
4. 20.3

Correct Option: D

Given that
V_TN = 0.84
k′_n = 40 µA/V²

		W			= 1
		L		₂

V₀ = 0.10 V
V_i = 5 V
For transistor M₂
V_DS = 0.1 V
V_GS₁ = V_i = 5 V
∴ V_DS < V_GS – V_TN, therefore the transistor M₂ work in the linear region
I_D₂ = I_D₁ = I_D

I_D₂ =	1	k'_n		W			. [2(V_GS₂ – V_Tn)V_DS₂ – V²_DS₂ ]…(A)
	2			L		₂

I_D₁ =	1	k_n′		W			(V_GS₁ – V_Tn)² …(B)
	2			L		₁

solving equation (A) and (B)

1. (5 – 0.1 – 0.8)² =		W			[2 . (5 – 0.8) 0.1 – (0.1)²]
		L		₁

(4.1)² =		W			[0·84 – 0.01]
		L		₁

or =		W			=	(4.1)²	= 20.25
		L		₁		0·83

Hence alternative (D) is the correct choice.

	W			for M₁ is:
	L		₁