By definition, op-amp constructed without any feedback elements are said to be open-loop configuration. The open-loop gain (A) of an op-amp is the difference between the voltage signals applied at its two input terminals, i.e. VOUT divided by, (VIN+ - VIN-), equals to A. i.e. A = VOUT/(VIN+ - VIN-)
To realize op-amp's open-loop gain, we can make a straight line graph, which shows the transfer characteristic of a linear amplifier.
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