Page 11 - Semester-IV-Electronics

 Gain for difference signal is, A = (1/2)*(A – A )
d 1 2

 Gain for common-mode signal, A = (A + A )
c 1 2

 For an ideal differential amplifier, A = 0
c

 The value of A is expected to be as large as possible as
d

compared to A .
c

 Efficiency of a differential amplifier is measured by magnitude

of ratio of A and A and is called common-mode rejection ratio
d
c
(CMRR).

 CMRR = ρ = =

 In decibel, CMRR = 20*log
10

 Now, v = A v + A v = = A v [1 + ] = A v [1 + ]
0
d d
d d
d d
c c

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