# Assume br wileyrazavi fundamentals of

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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 674 (1) 674 Chap. 12 Feedback M 1 I SS DD M 2 V in V M out V M 3 M 4 5 Figure 12.92 DD M V M out V 1 2 R D I in R F V b Figure 12.93 (a) Prove by inspection that the feedback is positive. (b) Assuming is very large and breaking the loop at the gate of , calculate the loop gain and prove that the feedback is positive. 31. Repeat Example 12.18 for the circuit illustrated in Fig. 12.94. DD M V M out V 1 2 R D I in R F V b R L Figure 12.94 32. Determine the closed-loop I/O impedances of the circuit shown in Fig. 12.94. 33. The amplifier depicted in Fig. 12.95 consists of a common-gate stage ( and ) and a feedback network ( , , and ). Assuming is very large and , compute the closed-loop gain and I/O impedances. 34. Repeat Problem 33 for the circuit illustrated in Fig. 12.96. Assume and are very small and neglect other capacitances. 35. A “laser diode” converts current to light (as in laser pointers). We wish to design a circuit that delivers a well-defined current to a laser diode. Shown in Fig. 12.97 is an example, where resistor measures the current flowing through and amplifier subtracts the resulting voltage drop from . Assume is very small and . (a) Following the procedure used in Example 12.21, determine the open-loop gain.
BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 675 (1) Sec. 12.9 Chapter Summary 675 R R V out M 1 R D V DD 1 2 M V b 2 I in Figure 12.95 V out M 1 R D V DD M V b 2 I in C 1 C 2 Figure 12.96 Q 1 R Laser Diode A 1 in V V CC I out 1 D M Figure 12.97 (b) Calculate the loop gain and the closed-loop gain. 36. Following the procedure used in Example 12.22, compute the open-loop and closed-loop output impedances of the circuit depicted in Fig. 12.97. 37. A student mistakenly replaces the common-emitter device in Fig. 12.97 with an emitter follower (Fig. 12.98). Repeat Problems 35 and 36 for this circuit and compare the results. 38. The amplifier in Fig. 12.98 can be realized as a common-base stage (Fig. 12.99). Repeat Problem 37 for this circuit. For simplicity, assume . 39. A student has adventurously replaced the PMOS common-source stage in Fig. 12.28 with an NMOS source follower (Fig. 12.100). (a) Prove by inspection that the feedback is positive. (b) Break the loop at the gate of , determine the loop gain, and prove that the feedback is positive. 40. Consider the feedback circuit depicted in Fig. 12.101. Assume . (a) Suppose the output quantity of interest is the collector current of , . Assuming

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BR Wiley/Razavi/ Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 676 (1) 676 Chap. 12 Feedback Q 1 R Laser Diode A 1 in V V CC I out 1 D M Figure 12.98 Q 1 R Laser Diode V CC I out 1 D M Q 2 in V R C Figure 12.99 DD M V M 1 2 R D I in R F V b Device Figure 12.100 Q V CC Q R C V b R I out R F M out V 1 2 I in Figure 12.101 is very small and is very large, determine the closed-loop gain and I/O impedances of the circuit.
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