In the RS422A standard a balance circuit is used for communi

In the RS-422-A standard a balance circuit is used for communication. Given the following parameters of the differential amplifier: common mode rejection ratio for the amplifier is 60 dB, a differential output voltage 10V for a differential input of 0.5 mV, find the common mode output voltage if the common mode input voltage is 5 mV.

a) 250 mV

b) 100 mV

c)100 uV

d) 250 uV

Solution

CMRR=Ad/Ac =60db

CMRR=10⁶

differential output voltage =10v

differential input voltage=0.5 mV

Ad=differential output voltage/differential input voltage=10v/0.5 mV=20x 10³

common mode input voltage= 5 mV

Ac= common mode output voltage / common mode input voltage

                =common mode output voltage/5 mV

Therefore CMRR=20x 10³/( common mode output voltage/5 mV)

common mode output voltage=100V