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BR Wiley/Razavi/Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 266 (1)
266 Chap. 5 Bipolar Amplifiers
(b) Draw the small-signal equivalent circuit.25. In the circuit of Fig. 5.124, A, , and .
VQ1
VCC= 2.5 V Ω
QB
2
Ω500
200
Figure 5.124
(a) Calculate such that carries a collector current of 1 mA.(b) Construct the small-signal equivalent circuit.
26. Determine the bias point of each circuit shown in Fig. 5.125. Assume ,
Q1
VCC
Ω200 Ω60 k
= 2.5 V
(a) (b)
Q
Q1
2
VCC
Ω Ω80 k
= 2.5 V
300
Figure 5.125
A, and .27. Construct the small-signal model of the circuits in Problem 26.28. Calculate the bias point of the circuits shown in Fig. 5.126. Assume ,
Q
Q1
2
VCC
Ω
= 2.5 V
Ω1 k
Ω
18 k
32 k
(a) (b)
Q1
VCC = 2.5 V
Ω Ω
Ω
18 k
32 k
100
Figure 5.126
A, and .29. Draw the small-signal model of the circuits in Problem 28.30. We have chosen in Fig. 5.127 to place at the edge of saturation. But the actual value
of this resistor can vary by . Determine the forward- or reverse-bias across the base-collector junction at these two extremes. Assume , A, and .
31. Calculate the value of in Fig. 5.128 such that sustains a reverse bias of 300 mV
HOMEWORK #4
Principles of Electronics- Winter 2015
Problem 1
a) For CE transistor shown below, find the overall small signal gain (V0/Vi) as a function of RS, RC and β, VA, and IC.
b) Next, determine the value of DC collector current IC that maximizes the small signal voltage gain.
c) Explain qualitatively why the gain falls at very high and very low collector currents. d) What is the voltafe gain at optimum IC? [Gray 3.2]
Problem 2
In Problem 1, assume RS=RC= 50 kΩ, and calculate IC. What is the DC voltage drop across RC? What is the voltage gain?
BR Wiley/Razavi/Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 270 (1)
270 Chap. 5 Bipolar Amplifiers
VCC
Q1outV
inV
RC
= 2.5 V
Ω200
Figure 5.137
44. Construct the small-signal model of the CE stage shown in Fig. 5.43(a) and calculate thevoltage gain. Assume .
45. Construct the small-signal model of the CE stage shown in Fig. 5.43(a) and prove that theoutput impedance is equal to if the Early effect is neglected.
46. Determine the voltage gain and I/O impedances of the circuits shown in Fig. 5.138. Assume.
Q1outV
inV
Q
VCC
2
R1
RE
VCC
Q1outV
inV
RC
Q2
VCC
Q1outV
inV
RC
Q 2
VCC
Q1outV
RC
Q 2
RinV
B
VCC
Q1outV
RC
RinV
BQ 2
VB
(c)
(d)
(a) (b)
(e)
Figure 5.138
47. Compute the voltage gain the I/O impedances of the circuits depicted in Fig. 5.139. Assume.
48. Using a small-signal equivalent circuit, compute the output impedance of a degenerated CEstage with . Assume .
49. Calculate the output impedance of the circuits shown in Fig. 5.140. Assume .50. Compare the output impedances of the circuits illustrated in Fig. 5.141. Assume .
BR Wiley/Razavi/Fundamentals of Microelectronics [Razavi.cls v. 2006] June 30, 2007 at 13:42 276 (1)
276 Chap. 5 Bipolar Amplifiers
Q1
Q2
Figure 5.155
70. In the emitter follower shown in Fig. 5.156, serves as a current source for the input device
Q1
R
VCC
E
inV
Q2
Vb
RCS
Figure 5.156
.(a) Calculate the output impedance of the current source, .(b) Replace and with the impedance obtained in (a) and compute the voltage gainand I/O impedances of the circuit.
71. Determine the voltage gain of the follower depicted in Fig. 5.157. Assume
Q1
VCC
outV
= 2.5 V
C1inV
Ω10 k
Ω1 k
C2
Ω100
Figure 5.157
A, , and V. (But for bias calculations, assume .) Also, assume thecapacitors are very large.
72. Figure 5.158 illustrates a cascade of an emitter follower and a common-emitter stage. As-