4.1 Defining the Virtual Short

Due to the op-amp’s extremely high open-loop gain, when it’s used in a stable circuit with feedback, a simple and powerful rule emerges: the voltage at the inverting input terminal is equal to the voltage at its non-inverting input terminal. It is critical to remember that this is a virtual short; there is no physical connection between the two terminals.

4.2 Why It’s the Key to Understanding

This single principle is the key to analyzing almost all basic op-amp circuits. By applying the virtual short concept, you can easily derive the behavior and gain of many different configurations without getting lost in complex internal circuit details.

Let’s use the virtual short concept to see how some of the most fundamental op-amp applications work.