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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