Which statement about a unity-gain buffer is accurate?

Which statement about a unity-gain buffer is accurate?

• A. It inverts the input signal.
• B. It scales the input by a factor of 2.
• C. It provides a high input impedance but high output impedance.
• D. It provides a unity gain, high input impedance, and low output impedance to isolate stages.

Answer: (D)

A unity-gain buffer, or voltage follower, uses negative feedback to make its output follow the input, giving a gain of about one. Because the op-amp input impedance is very high, it draws almost no current from the source, so the signal isn’t loaded. The closed-loop behavior also yields a very low output impedance, so it can drive the next stage without the signal dropping. It does not invert the signal and it does not amplify by a factor of two. So the description of unity gain, high input impedance, and low output impedance to isolate stages is the accurate one.

A unity-gain buffer, or voltage follower, uses negative feedback to make its output follow the input, giving a gain of about one. Because the op-amp input impedance is very high, it draws almost no current from the source, so the signal isn’t loaded. The closed-loop behavior also yields a very low output impedance, so it can drive the next stage without the signal dropping. It does not invert the signal and it does not amplify by a factor of two. So the description of unity gain, high input impedance, and low output impedance to isolate stages is the accurate one.