Which of the following circuits is known for maintaining the input voltage levels without change?

A buffer circuit is designed specifically to maintain the input voltage levels without change. It acts as a voltage follower, meaning that whatever voltage is applied at the input is reflected at the output without any amplification or attenuation. This characteristic makes buffers highly effective for isolating different parts of a circuit and preventing loading effects that could alter the performance of various components. They ensure that the signal remains consistent and that the output voltage accurately matches the input voltage, which is crucial in applications where signal integrity is important.

In contrast, an inverter changes the input signal’s logic state (from high to low or vice versa), while logical gates such as NAND and OR gates perform specific logical functions that inherently alter the relationship between inputs and outputs. Therefore, these alternatives do not maintain input voltage levels unchanged as a buffer does.