In the equivalent diagram of BJT, Vbe and rbe represent the base voltage and resistance. gmVbe is a current source, which represents the current gain. Since gm = Ic/Vt Vt/Ic = 1/gm Does this mean the impedance of the current source is 1/gm ? I know this sounds a bit weird. It's because of a hw problem posted here - https://www.physicsforums.com/showthread.php?t=569541 (the input resistance of the diode connected BJT is (rbe||1/gm).