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[EKT104 ANALOG ELECTRONIC CIRCUITS]
Sem. 2 2014/2015
Tutorial 5
MULTISTAGE AMPLIFIERS
1. Each transistor in the Darlington pair shown in Figure 1 below has β =100. Find the overall
current gain of both transistors, neglecting the leakage current.
Figure 1
2. In the amplifier circuit shown in Figure 2, determine the value of R such that Q2 is biased at VCE2 =
7.5 volts. Assume Q1 and Q2 to be identical with VBE = 0.7 volts.
Figure 2
1
School of Computer and Communication Engineering, UniMAP
[EKT104 ANALOG ELECTRONIC CIRCUITS]
Sem. 2 2014/2015
3. Design the circuit shown in Figure 3, called a cascode circuit, to meet the following
specifications: VCE1 = VCE2 = 2.5 V, VRE = 0.7 V, IC1 ≅ IC2 ≅ 1mA, and IR1 ≅ IR2 ≅ IR3 ≅
0.10mA.
Figure 3
2
School of Computer and Communication Engineering, UniMAP
[EKT104 ANALOG ELECTRONIC CIRCUITS]
Sem. 2 2014/2015
4. Consider the circuit in Figure 4. Let β = 100, VB E (on) = 0.7 V, and VA = ∞ for each
transistor. Assume RB = 10kΩ, RC = 4kΩ, IEo = 1 mA, V + = 5 V, and V − = −5 V .
(a) Determine the Q-point values for each transistor.
(b) Calculate the small-signal hybrid-π parameters for each transistor.
(c) Find the overall small-signal voltage gain Av =Vo/Vs.
(d) Find the input resistance Ri.
Figure 4
3
School of Computer and Communication Engineering, UniMAP
[EKT104 ANALOG ELECTRONIC CIRCUITS]
Sem. 2 2014/2015
5. Consider the cascode circuit in Figure 5. Let β = 100, VBE(on)=0.7V, and VA =∞for
each transistor. Let VCC =9V and RL =10kΩ.
(a) Design the circuit such that VCE1 =VCE2 =2.5V, VRE =0.7V, IC1 ≅ IC2 ≅ 1 mA,
and IR1 ≅ IR2 ≅ IR3 ≅ 0.1 mA. (Hint: Neglect the dc base currents.)
(b) Determine the small-signal hybrid-π parameters for each transistor.
(c) Determine the small-signal voltage gain Av = Vo/Vs .
Figure 5
4
School of Computer and Communication Engineering, UniMAP
[EKT104 ANALOG ELECTRONIC CIRCUITS]
Sem. 2 2014/2015
6. In the current mirror BJT circuit shown in Figure 6 below, assume that the emitter area of
transistor Q1 is half that of transistor Q2. Calculate the approximate value of current Io.
Figure 6
5
School of Computer and Communication Engineering, UniMAP
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