If an op-amp had nonzero output impedance, what would be the effect when driving a load?

If an op-amp had nonzero output impedance, what would be the effect when driving a load?

• A. The output would stay perfect regardless of load
• B. The op-amp would not function
• C. The output could drop or lose signal integrity depending on the load
• D. The gain would become infinite

Answer: (C)

The key idea is that a real op-amp isn’t an ideal voltage source; it has a finite output impedance. When you connect a load, the output stage and the load form a simple network, so the voltage at the load is the result of a divider between the op-amp’s output impedance and the load resistance. If the load draws current, part of the op-amp’s attempt to drive the signal drops across its own output impedance, causing the load voltage to fall and potentially distort the waveform or reduce fidelity as the current demand changes. In other words, the output can sag or lose signal quality depending on how heavy the load is. This happens less with a very high-load-resistance (light load) and more with a low-resistance (heavy load), where the drop becomes more noticeable and the effective performance of the amplifier (gain seen at the load, bandwidth, and stability) can shift. The other statements would only be true if the output were an ideal voltage source with zero output impedance, which is not the case here, or would imply nonsensical outcomes like infinite gain.

The key idea is that a real op-amp isn’t an ideal voltage source; it has a finite output impedance. When you connect a load, the output stage and the load form a simple network, so the voltage at the load is the result of a divider between the op-amp’s output impedance and the load resistance. If the load draws current, part of the op-amp’s attempt to drive the signal drops across its own output impedance, causing the load voltage to fall and potentially distort the waveform or reduce fidelity as the current demand changes. In other words, the output can sag or lose signal quality depending on how heavy the load is.

This happens less with a very high-load-resistance (light load) and more with a low-resistance (heavy load), where the drop becomes more noticeable and the effective performance of the amplifier (gain seen at the load, bandwidth, and stability) can shift. The other statements would only be true if the output were an ideal voltage source with zero output impedance, which is not the case here, or would imply nonsensical outcomes like infinite gain.