Correct Option: A

VB = Vi		R2
		R1 + R2

By using superposition principle.

Vo = –	R3	. V2 + VB.		1 +	R3
	R4				R4

or Vo = –	R3	. V2 + V1.		R2		·		R4 + R3		............(i)
	R4			R1 + R2				R4

we know,

Vc =	V1 + V2	.............(ii)
	2

V_d = V₁ – V₂ …(iii)
from equations (ii) and (iii)

V1 = Vc +	Vd	.............(iv)
	2

V2 = Vc –	Vd	.............(v)
	2

Substituting these values in equation (i)

Vo = –

R3

Vc –

Vd

+

Vc +

Vd

R2

+

R4 + R3

R4

2

2

R1 + R2

R4

or Vo = Vc

R2

·

R4 + R3

-

R3

+

Vd

R2

R4 + R3

R3

...........(vi)

R1 + R2

R4

R4

2

R1 + R2

R4

R4

Since, CMRR =	AdM
	AcM

where AdM =	Vo	|Vd = 0 so from equation (vi)
	Vd

AdM	V0	=	1		R2			R4 + R3		+	R3
	Vd		2		R1 + R2			R4			R4

and AdM =	Vo	|Vd = 0
	Vd

AdM =		R2			R4 + R3		-	R3
		R1 + R2			R4			R4

finally

CMRR =	1		R3(R1 + R2) + R2(R4 + R3)
	2		R3(R1 + R2) - R1(R4 + R3)

Hence alternative (A) is the correct choice.