Through all my reading of op-amp literature, I think the explanation for common-mode voltages and common-mode rejection *suck*. The definitions, in my opinion, overlap and fail to relate those definitions of common-mode voltages to the op-amps 'common-mode rejection'.
A typical inverting or non-inverting amplifier does not 'reject' the common mode voltage. For example, there is no common-mode voltage on an inverting amplifier. The non-inverting input is grounded, and the summing junction is held at virtual ground. There is nothing to 'reject.'
The common-mode voltage of a non-inverting amplifier is the voltage on the non-inverting input. This will be dynamic if one is amplifying an AC signal. The common-mode voltage follows the input sinewave. That same sine-wave will pass on through to the output, multiplied by the gain if not a voltage follower.
It is the same with DC. With DC voltages, the common-mode will still show up on the output. It is not rejected to cause a 0V output.
Terrible definitions, or at least very disorganized.
A typical inverting or non-inverting amplifier does not 'reject' the common mode voltage. For example, there is no common-mode voltage on an inverting amplifier. The non-inverting input is grounded, and the summing junction is held at virtual ground. There is nothing to 'reject.'
The common-mode voltage of a non-inverting amplifier is the voltage on the non-inverting input. This will be dynamic if one is amplifying an AC signal. The common-mode voltage follows the input sinewave. That same sine-wave will pass on through to the output, multiplied by the gain if not a voltage follower.
It is the same with DC. With DC voltages, the common-mode will still show up on the output. It is not rejected to cause a 0V output.
Terrible definitions, or at least very disorganized.