Mansoura University
Faculty of Engineering
Communication Engineering Department
Second Year Communication
Microelectronic Circuits
Sheet (5)
[1] A particular BJT operating at Ic = 2 mA has Cµ = 1 pF, Cπ = 10 pF,
and β = 150. What are fT and fB for this situation?
[2] A particular small-geometry BJT has fT of 5 GHz and Cµ = 0.1 pF
when operated at Ic = 0.5 mA.
(a) What is Cπ in this situation?
(b) Find gm.
(c) For β = 150, find rπ and fB.
[3] Consider the common-emitter amplifier of Fig. 1under the following
conditions: Rsig = 5 kΩ, R1 = 33 kΩ, R2 = 22 kΩ, RE = 3.9 kΩ, Rc =
4.7 kΩ, RL = 5.6 kΩ, Vcc = 5 V. The dc emitter current can be shown
to be IE = 0.3 mA, at which β = 120, ro = 300 kΩ, and rx = 50 Ω.
(a) For midband frequency region, Find the input resistance Rin and
the midband gain AM.
(b) If the transistor is specified to have fT = 700 MHz and Cµ = 1 pF,
find the upper 3-dB frequency fH.
[4] The amplifier shown in Fig.2 has Rsig = RL = 1 kΩ, Rc = 1 kΩ, RB =
47 kΩ, β = 100, Cµ = 0.8 pF, and fT = 600 MHz.
(a) Find the dc collector current of the transistor.
(b) Find gm and rπ.
(c) Neglecting ro, find the midband voltage gain from base to
collector (neglect the effect of RB).
(d) Use the gain obtained in (c) and the Miller theorem to find the
component of Rin that arises as a result of RB. Hence find Rin.
(e) Find the overall gain at midband.
(f) Find Cin.
(g) Find fH.
Page 1
Mansoura University
Faculty of Engineering
Communication Engineering Department
Fig.1
Fig.2
Page 2
Second Year Communication
Microelectronic Circuits
Sheet (5)