Which transistor configuration is known for providing the highest input impedance?

The common collector configuration is known for providing the highest input impedance among the various transistor configurations. In this configuration, the input signal is applied to the base-emitter junction while the output is taken from the emitter. Because the collector terminal is connected directly to a constant voltage (such as Vcc), the base-emitter junction is less susceptible to variations, which effectively raises the impedance presented to the input signal.

This high input impedance is a particularly desirable characteristic in applications such as buffer circuits, where the goal is to prevent loading effects on the previous stage of circuitry. In this way, the common collector serves to couple signals from low-impedance sources to high-impedance loads while maintaining signal integrity.

Other configurations, like common emitter, tend to have lower input impedances due to the direct connection of the input signal to the base, which is influenced more by the transistor's characteristics. The common base configuration indeed has the lowest input impedance among practical configurations. Thus, the common collector is typically chosen where high input impedance is critical, making it the correct choice for the given question.