Exam Questions Papers - Engineering

Q1:

For a npn BJT transistor fβ is 1.64 x 108 Hz. Cμ = 10-14 F; Cp = 4 x 10-13 F and DC current gain is 90. Find fT and gm (fβ = cut off frequency, Cμ = capacitance, Cp = parasitic capacitance, gm = transconductance, fT = gain BW product)

A fT = 1.47 x 1010 Hz ; gm = 38 milli mho

B fT = 1.64 x 108 Hz ; gm = 30 milli mho

C fT = 1.47 x 109 Hz ; gm = 38 mho

D fT = 1.33 x 1012 Hzgm = 0.37 m-mh

ANS:A - fT = 1.47 x 1010 Hz ; gm = 38 milli mho

fT = 90 x 1.64 x 108 = 1.47 x 1010 Hz gm = 2pfT(Cμ + Cp) = 2 x p x 1.47 x 1010 = (10-14 + 4 x 10-13) gm= 38 mμ.