Common-mode signal

[alphacat]

Hello.

I though that a common mode signal is an unwanted signal that adds directly to both input signals, and therefore will be eliminated when the differential amplifier processes the difference of the input signals.

So why is it said that the common mode signal is the half-sum of the input voltages?
Vcm = ½(V1 + V2)

Thanks.

 

[ericgibbs]

Hello.

I though that a common mode signal is an unwanted signal that adds directly to both input signals, and therefore will be eliminated when the differential amplifier processes the difference of the input signals.

So why is it said that the common mode signal is the half-sum of the input voltages?
Vcm = ½(V1 + V2)

Thanks.

hi,
This explains it.
**broken link removed**

 

[alphacat]

Thank you very much!

 

[AdrianN]

For the record, the website name changed to
Mastering Electronics Design : The Differential Amplifier Common-Mode Error - Part 2