What is cut-off frequency (fβ)?

Q.  The cut-off frequency (fβ) is basically the frequency at which the short circuit __________
- Published on 23 Sep 15

a. CB gain of transistor drops by 3 dB from its value at low frequency
b. CE gain of transistor drops by 3 dB from its value at low frequency
c. CC gain of transistor drops by 3 dB from its value at low frequency
d. None of the above

ANSWER: CE gain of transistor drops by 3 dB from its value at low frequency

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    Discussion

  • Satyawati   -Posted on 30 Sep 15
    Cut-off frequency (fβ) is basically the frequency at which short circuit CE gain of transistor drops by 3dB from its value at low frequency.

    Thus, the frequency range upto the cut-off frequency(fβ) is regarded as the bandwidth of circuit. Also, the current gain reduces to 70.7% of the low frequency current gain.

    Similarly, the frequency at which short circuit CB gain of transistor drops by 3dB from its value at low frequency is known as cut-off frequency (fα).

    The relationship between these cut-off frequencies indicates that the 3dB frequency of CB configuration is (1 + hfe) times greater or higher as compared to that of CE configuration.

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