Differential amplifier using BJT ;. Measurement of CMRR.

[mohangupta84]

i wantto know the outp[ut when amplifier is operated in commom mode,,i tried so many times with different input but i got output voltage as 0 volt.can you suggest me the way i calculate cmrr value.


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the image i attached is the differential mode,,where output voltage is 0.1 microvolt..

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R13=R14=952 MEGA OHM.
R15=R16=204 OHM.

 

[crutschow]

With ideal identical devices in your simulation the CMRR for the difference signal will be essentially infinite, as you measured.

Note that your circuit is not a true differential stage since it does not have a common impedance in the emitter connections. You just have two single-ended stages being feed the same signal.