CE Short circuit - Unity gain frequency

Q.  Which among the following represents the frequency at which short circuit CE current gain acquires unit magnitude?
- Published on 23 Sep 15

a. fα
b. fβ
c. fT
d. None of the above

ANSWER: fT

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    Discussion

  • Satyawati   -Posted on 30 Sep 15
    Apart from the cut-off frequency, the frequency at which the short-circuit CE current gain acquires unity magnitude (AI = 1) is called as 'Unity gain frequency'.

    This parameter is generally represented by 'fT''.

    The relationship between the unity gain frequency (fT) and cut-off frequency (fβ) is specified as,

    fT = hfe fβ

    The unity gain frequency is very crucial high frequency characteristics of a transistor, whose value is dependent on the operating conditions.

    Variation in unity gain frequency also affects 'Ic' & 'hfe'. Experimentally, it is very arduous to measure the unity gain frequency because it is inconveniently high. Therefore, it is usually measured at appreciably low frequency.

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