A common mode input voltage can represent which of the following in a circuit?

A common mode input voltage can represent which of the following in a circuit?

• A. An undesirable circuit input
• B. A desired signal
• C. The primary signal
• D. A zero-input condition

Answer: (A)

Common-mode input voltage is the portion of the signal that appears equally on both inputs of a differential amplifier. It often comes from noise, ground differences, or supply ripple coupling into the circuit. Because this voltage does not carry information about the difference between the inputs, it is generally unwanted; the amplifier is designed to reject it and pass only the differential signal. In real circuits, some of this common-mode voltage can still influence the output due to finite common-mode rejection and other nonidealities, so it’s treated as an undesirable circuit input rather than the intended signal.

Common-mode input voltage is the portion of the signal that appears equally on both inputs of a differential amplifier. It often comes from noise, ground differences, or supply ripple coupling into the circuit. Because this voltage does not carry information about the difference between the inputs, it is generally unwanted; the amplifier is designed to reject it and pass only the differential signal. In real circuits, some of this common-mode voltage can still influence the output due to finite common-mode rejection and other nonidealities, so it’s treated as an undesirable circuit input rather than the intended signal.