- Common-mode voltage gain refers to the amplification given to signals that appear on both inputs relative to the common (typically ground).
- You will recall from a previous discussion that a differential amplifier is designed to amplify the difference between the two voltages applied to its inputs.
- Thus, if both inputs had +5 volts, for instance, with respect to ground, then the difference would be zero. Similarly, the output would be zero. This defines ideal behavior and is a characteristic of an ideal op amp.
- In a real op amp, common-mode voltages can receive some amplification and thus depart from the desired behavior. Since we are currently defining ideal characteristics you should remember that an ideal op amp has a common-mode voltage gain of zero.
- This means the output is unaffected by voltages that are common to both inputs (i.e., no difference). Figure 1.13 further illustrates the measurement of common-mode voltage gains
Source : Science Direct
