What is Common mode bias voltage

[Advark]

common mode bias

Hi, can anyone explain to me

 

[rahat]

what is common mode

as far as i know , common mode b. vlt. is the dc voltage, upon which the ac voltage(which is to be amplified) is superimposed.

for more details: 'Design of Analog CMOS Integrated circuits' by Behzad Razavi,p-100.

 

[mahdi.fersi]

what is common mode

The Common Mode (CM) is a mode in which the DC operating point is fixed. The circuit in this point has a linear behavior.

 

[salerno]

what is common mode voltage

In a differential operational amplifier, you have two terminals, the positive one, Vp, and the negative one, Vn. Therefore, you have a differential signal Vd=Vp-Vn, and a common mode signal, Vcm=(Vp+Vn)/2.
The amplifier works properly if the common mode voltage is set accurately by a common mode feedback loop. If the common mode DC voltage is not set correctly, the amplifier saturates to its rails (either VDD, either VSS) and it not able to amplifier the differential AC signal.