Op-amps have a high gain (around 105, or 100 dB). To achieve stable operation, op-amps are used with negative feedback. The gain of an op-amp without feedback is called the open-loop gain whereas the gain of an op-amp with a feedback circuit is called the closed-loop gain. Figure 1 gives a Bode plot of an op-amp, which shows the relationship between the open-loop and closed-loop gains. The open-loop gain halves when frequency doubles. (On a logarithmic scale, it has a slope of -6 dB/oct or -20 dB/dec.)
The closed-loop gain (Gv) of the negative feedback circuit shown in Figure 2 is calculated as -R2/R1.