# Common mode voltage in transconductance amplifier

#### level1IC

Joined Nov 26, 2017
6
Hello
Can some tell me what is common mode voltage of any differentail amplifier. Is it a DC voltage or can be an AC voltage? because input of any differential pair is given as : vi1= VCM+vid/2 and vi2 = VCM-vid/2. what is this VCM AC vloltage or DC voltage or the transient voltage (V amplitude) which we apply for doing transient analysis?

#### Danko

Joined Nov 22, 2017
1,365
Hello
Can some tell me what is common mode voltage of any differentail amplifier. Is it a DC voltage or can be an AC voltage? because input of any differential pair is given as : vi1= VCM+vid/2 and vi2 = VCM-vid/2. what is this VCM AC vloltage or DC voltage or the transient voltage (V amplitude) which we apply for doing transient analysis?
Common mode voltage is a DC or an AC voltage and it is literally common (appearing on both) inputs, in the same polarity.
For example see https://electronics.stackexchange.c...age-stand-for-in-an-instrumentation-amplifier .