(b)Common Base

1.On small signal analysis of BJT CB configuration, we get the current gain as Ai =$(r_\pi+\beta r_o)\over(r_\pi+(\beta+1)r_o)$

2.The given expression for current gain Ai evaluates approximately to unity

1. Thus,as output current is almost equal to input current,COMMON BASE CIRCUIT behaves as a constant current source