Question

In common base configuration current gain is less than 1 but still be can have a voltage gain. How?

Answer 1

The reason for high gain is very high value of output resistance.  

Explanation:

Common emitter configuration is the only which have very high gain and inverted output. In this case the current of the output is less than the input current so current gain is less than unity. But we have very high value of the output resistance which makes the gain high. It can be shown by analyzing following formula:

                                                      Gain = A = - βRc?/rie