Which op-amp configuration is considered to be operated in an open-loop mode?

In op-amp configurations, open-loop mode refers to the operational amplifier being used without any feedback connections, meaning that the output is not being fed back to the inverting input. This configuration leads to a very high gain and is typically used in applications where the precise threshold levels are important, such as in a comparator.

The comparator's primary function is to compare two input voltages and indicate which one is higher. When used in this manner, the op-amp provides a simple output that switches states based on the relation between the two inputs, without any feedback influencing the gain, thus aligning with the characteristics of open-loop operation.

In contrast, other configurations like integrating, voltage follower, and inverting amplifier rely on feedback mechanisms. These feedback connections stabilize the output, reduce gain, and establish a defined relationship between input and output. Therefore, they do not operate in an open-loop mode, as they depend on the feedback to regulate performance.