In a linear closed-loop op-amp, the differential input voltage is approximately what value?

In a linear closed-loop op-amp, the differential input voltage is approximately what value?

• A. Approximately 0 V
• B. Approximately 1 V
• C. -1 V
• D. Equal to output voltage

Answer: (A)

In a linear closed-loop op-amp with negative feedback, the circuit adjusts the output so the two input terminals sit at nearly the same voltage—the so-called virtual short. The op-amp has a very large open-loop gain, so only a tiny difference between inputs is needed to drive the output to the required level. The feedback then reduces that difference until it’s effectively zero in the linear operating region. So the differential input voltage is approximately zero volts (with a tiny residual value in real devices, depending on gain and conditions).

In a linear closed-loop op-amp with negative feedback, the circuit adjusts the output so the two input terminals sit at nearly the same voltage—the so-called virtual short. The op-amp has a very large open-loop gain, so only a tiny difference between inputs is needed to drive the output to the required level. The feedback then reduces that difference until it’s effectively zero in the linear operating region. So the differential input voltage is approximately zero volts (with a tiny residual value in real devices, depending on gain and conditions).