Question

Problem 1. Class-AB Power Amplifier with Additional Input Transistors Consider the circuit of the figure below. Assume that the resistance r_e in the emitter for the transistors is not negligible. Furthermore, assume that the top and bottom halves of the circuit are perfectly matched. i) (10 points) What is the function of the Q1–Q2 circuit? Explain your answer. ii) (10 points) For this circuit operated near v1 = 0 and fed with a signal source having zero resistance, show that the output resistance is given by Rout = 1/2 [R3 + r_e3 + (R1 || r_e1)/(?3 + 1)] iii) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For v1 = 0 and RL = ?, determine the quiescent current in each of the four transistors and vO. iv) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For RL = ?, determine iC1, iC2, iC3, iC4, and vO for v1 = +10 V and ?10 V. v) (10 points) Repeat iv) for RL = 100 ?.

          Problem 1. Class-AB Power Amplifier with Additional Input Transistors

Consider the circuit of the figure below. Assume that the resistance r_e in the emitter for the transistors is not negligible. Furthermore, assume that the top and bottom halves of the circuit are perfectly matched.

i) (10 points) What is the function of the Q1–Q2 circuit? Explain your answer.

ii) (10 points) For this circuit operated near v1 = 0 and fed with a signal source having zero resistance, show that the output resistance is given by
Rout = 1/2 [R3 + r_e3 + (R1 || r_e1)/(?3 + 1)]

iii) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For v1 = 0 and RL = ?, determine the quiescent current in each of the four transistors and vO.

iv) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For RL = ?, determine iC1, iC2, iC3, iC4, and vO for v1 = +10 V and ?10 V.

v) (10 points) Repeat iv) for RL = 100 ?.

Problem 1. Class-AB Power Amplifier with Additional Input Transistors

Consider the circuit of the figure below. Assume that the resistance re in the emitter for the transistors is not negligible. Furthermore, assume that the top and bottom halves of the circuit are perfectly matched.

i) (10 points) What is the function of the Q1–Q2 circuit? Explain your answer.

ii) (10 points) For this circuit operated near v1 = 0 and fed with a signal source having zero resistance, show that the output resistance is given by
Rout = 1/2 [R3 + re3 + (R1 || re1)/(?3 + 1)]

iii) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For v1 = 0 and RL = ?, determine the quiescent current in each of the four transistors and vO.

iv) (10 points) Let R1 = R2 = 5 k?, R3 = R4 = 0 ?, and VCC = 15 V. Moreover, let the transistors be matched with the saturation current IS = 3.3 × 10^?14 A and ? = 200. For RL = ?, determine iC1, iC2, iC3, iC4, and vO for v1 = +10 V and ?10 V.

v) (10 points) Repeat iv) for RL = 100 ?.

Added by Eric B.

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