Alpha cutoff frequency

Alpha cutoff frequency, or ${\displaystyle f_{\alpha }}$ is the frequency at which the common base DC current gain ${\displaystyle \alpha }$ drops to 0.707 of its low frequency value. The common base DC current gain is the ratio of a transistor's collector current to the transistor's emitter current, or ${\displaystyle \alpha ={\frac {i_{C}}{i_{E}}}}$.¹