In the common base amplifier, the input impedance, when compared to the output impedance is:

The common base amplifier is unique among transistor configurations because its input signal is applied across the forward-biased base-emitter junction. Because this junction is forward-biased, it readily conducts current and presents a very low resistance to the incoming signal, resulting in a very low input impedance. In stark contrast, the output is taken from the reverse-biased base-collector junction, which has a very high impedance. This dramatic difference makes the common base amplifier highly useful as an impedance-matching device, often used to step up from a low impedance source to a high impedance load. Options suggesting the input impedance is high or only slightly different from the output are incorrect, as the massive difference between the low input and high output impedances is the defining characteristic of this circuit.