# 2 determine the small signal input resistance of the

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2. Determine the small-signal input resistance of the circuits shown in Fig. 5.104. Assume all diodes are forward-biased. (Recall from Chapter 3 that each diode behaves as a linear 1 D R 1 D 2 (c) (a) (b) in R 1 D R 1 in R D 2 1 D R 1 in R Figure 5.104 resistance if the voltage and current changes are small.) 3. Compute the input resistance of the circuits depicted in Fig. 5.105. Assume . Q 1 R 1 R 2 in R Q 1 R 1 in R Q 1 Q in R 2 Q 1 V CC Q 2 in R V CC V CC V CC (c) (d) (a) (b) Figure 5.105 4. Compute the output resistance of the circuits depicted in Fig. 5.106. 5. Determine the input impedance of the circuits depicted in Fig. 5.107. Assume . 6. Compute the output impedance of the circuits shown in Fig. 5.108. 7. Compute the bias point of the circuits depicted in Fig. 5.109. Assume ,

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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 261 (1) Sec. 5.5 Chapter Summary 261 Q 1 V B R 1 out R V Q 1 R B R out B Q 1 Q 2 R out Q 1 V CC Q 2 R out (c) (d) (a) (b) Figure 5.106 Q 1 V CC R 1 in R Q 1 V CC Ideal V B in R R 1 Q V CC V B in R R 1 Q 1 2 Q 1 V CC in R Q 2 Q 1 V CC in R Q 2 (c) (d) (a) (b) (e) Figure 5.107 Q 1 V CC R Q V B Q 1 2 (a) out R C R out (b) Figure 5.108 A, and . 8. Construct the small-signal equivalent of each of the circuits in Problem 7. 9. Calculate the bias point of the circuits shown in Fig. 5.110. Assume , A, and . 10. Construct the small-signal equivalent of each of the circuits in Problem 9. 11. Consider the circuit shown in Fig. 5.111, where , A, and .
BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 262 (1) 262 Chap. 5 Bipolar Amplifiers V CC = 2.5 V Q 1 500 Q 1 100 k 1 k Q 2 V CC = 2.5 V Q 1 100 k 1 k V CC = 2.5 V 0.5 V (c) (a) (b) 100 k Figure 5.109 V CC = 2.5 V Q 1 Q 1 Q 2 V CC = 2.5 V Q 1 1 k V CC = 2.5 V 0.5 V (c) (b) 3 k 34 k 16 k 16 k 9 k 13 k 12 k (a) 500 Figure 5.110 V CC = 2.5 V Q 1 2 k 3 k R B Figure 5.111 (a) What is the minimum value of that guarantees operation in the active mode? (b) With the value found in , how much base-collector forward bias is sustained if rises to 200? 12. In the circuit of Fig. 5.112, and . V CC = 2.5 V Q 1 30 k 50 k 3 k Figure 5.112 (a) If the collector current of is equal to 0.5 mA, calculate the value of .

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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 263 (1) Sec. 5.5 Chapter Summary 263 (b) If is biased at the edge of saturation, calculate the value of . 13. The circuit of Fig. 5.113 must be designed for an input impedance of greater than 10 k and V CC = 2.5 V Q 1 R 1 R 2 5 k Figure 5.113 a of at least . If , A, and , determine the minimum allowable values of and . 14. Repeat Problem 13 for a of at least . Explain why no solution exists. 15. We wish to design the CE stage depicted in Fig. 5.114 for a gain ( ) of with an V CC Q 1 R 1 R 2 R C Figure 5.114 output impedance of . What is the maximum achievable input impedance here? Assume . 16. The circuit of Fig. 5.115 is designed for a collector current of 0.25 mA. Assume V CC Q 1 R 1 R E = 200 R C 3 k R 2 10 k = 2.5 V Figure 5.115 A, , and .
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