Open-loop gain

Open loop gain of an operational amplifier is a gain obtained when no feedback is used in the circuit. Open loop gain is usually exceedingly high, ideal operational amplifier has infinite open loop gain. Typically an op-amp may have an open loop gain of around $10^{5}$. Normally feedback is applied around the op-amp so that the gain of the overall circuit is defined and kept to a figure which is more usable. However the very high gain of the op-amp enables considerable levels of feedback to be applied to achieve required performance. The open loop gain of an operational amplifier falls very rapidly with increasing frequency. Along with slew rate, this is one of the reasons why operation amplifiers have limited bandwidth.