The condition where the inverting and non-inverting inputs are equal due to negative feedback is known as what?

The condition where the inverting and non-inverting inputs are equal due to negative feedback is known as what?

• A. Virtual short
• B. Virtual ground
• C. Open loop
• D. Saturation

Answer: (A)

Negative feedback drives the voltages at the two inputs to nearly the same value. Because an op-amp has a very large open-loop gain, the output shifts until the difference between the inverting and non-inverting inputs is essentially zero. This creates a virtual short between the inputs: they sit at the same voltage even though there isn’t a real wire connecting them. The key is that the input terminals draw almost no current, thanks to the op-amp’s high input impedance, so it acts like a short in voltage, not a physical connection. A virtual ground is a special case where that common voltage happens to be zero volts, typically when the non-inverting input is tied to ground; in general, the equal-input condition can be at any reference voltage. Open loop and saturation describe states without negative feedback or with output limiting, and do not produce equal input voltages.

Negative feedback drives the voltages at the two inputs to nearly the same value. Because an op-amp has a very large open-loop gain, the output shifts until the difference between the inverting and non-inverting inputs is essentially zero. This creates a virtual short between the inputs: they sit at the same voltage even though there isn’t a real wire connecting them. The key is that the input terminals draw almost no current, thanks to the op-amp’s high input impedance, so it acts like a short in voltage, not a physical connection. A virtual ground is a special case where that common voltage happens to be zero volts, typically when the non-inverting input is tied to ground; in general, the equal-input condition can be at any reference voltage. Open loop and saturation describe states without negative feedback or with output limiting, and do not produce equal input voltages.