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dB PROBLEMS ⏐⏐⏐ 1091<br />

SECTION 23.14 Other Properties and a<br />

Summary Table<br />

45. A bipolar transistor amplifier has the following gain:<br />

160<br />

Av ��������<br />

Hz<br />

�1 � j �100�<br />

f ��1 � j � 130 Hz<br />

f<br />

f<br />

�<br />

f ��1 � j �� 20kHz��1<br />

� j �� 50 kHz�<br />

a. Sketch the normalized Bode response A′ vdB �<br />

(A v /A vmax )| dB, and determine the bandwidth of the<br />

amplifier. Be sure to note the corner frequencies.<br />

b. Sketch the phase response, and determine a frequency<br />

where the phase angle is relatively close to 45°.<br />

46. A JFET transistor amplifier has the following gain:<br />

�5.6<br />

Av ����������<br />

Hz<br />

�1 � j �10 �<br />

f ��1 � j � 45 Hz<br />

�<br />

f ��1 � j � 68 Hz<br />

f<br />

f<br />

�<br />

f ��1 � j �� 23 kHz��1<br />

� j �� 50 kHz�<br />

a. Sketch the normalized Bode response A′ vdB �<br />

(Av /Avmax | dB), and determine the bandwidth of the<br />

amplifier. When you normalize, be sure that the maximum<br />

value of A′ v is �1. Clearly indicate the cutoff<br />

frequencies on the plot.<br />

b. Sketch the phase response, and note the regions of<br />

greatest change in phase angle. How do the regions<br />

correspond to the frequencies appearing in the function<br />

Av? 47. A transistor amplifier has a midband gain of �120, a<br />

high cutoff frequency of 36 kHz, and a bandwidth of<br />

35.8 kHz.In addition, the actual response is also about<br />

�15 dB at f � 50 Hz. Write the transfer function Av for<br />

the amplifier.<br />

48. Sketch the Bode plot of the following function:<br />

Av �<br />

49. Sketch the Bode plot of the following function:<br />

Av �<br />

50. Sketch the Bode plot of the following function:<br />

Av �<br />

*51. Sketch the Bode plot of the following function:<br />

(1 � j f/1000)(1 � j f/2000)<br />

Av ����<br />

(1 � j f/3000)<br />

*52. Sketch the Bode plot of the following function (note the<br />

presence of q rather than f ):<br />

40(1 � j 0.001q)<br />

Av ����<br />

( j 0.001q)(1 � j 0.0002q)<br />

2<br />

0.05<br />

��<br />

0.05 � j 100/f<br />

200<br />

��<br />

200 � j 0.1f<br />

0 dB<br />

400 Hz<br />

–3 dB<br />

j f/1000<br />

����<br />

(1 � j f/1000)(1 � j f/10,000)<br />

+<br />

Vi = 1 V∠0°<br />

–<br />

Llow 4.7 mH<br />

Clow 400 Hz<br />

0 dB<br />

–3 dB<br />

L 2(mid)<br />

C 0.39 mH<br />

1(mid) 39 �F<br />

C2(mid) L1(mid) 4.7 mH<br />

39 �F<br />

5 kHz<br />

–3 dB<br />

2.7 �F<br />

8 �<br />

8 �<br />

0 dB<br />

5 kHz<br />

–3 dB<br />

SECTION 23.15 Crossover Networks<br />

*53. The three-way crossover network of Fig. 23.120 has a<br />

12-dB rolloff at the cutoff frequencies.<br />

a. Determine the ratio Vo /Vi for the woofer and tweeter<br />

at the cutoff frequencies of 400 Hz and 5 kHz, respectively,<br />

and compare to the desired level of 0.707.<br />

Chigh 2.7 �F<br />

Lhigh FIG. 23.120<br />

Problems 53 and 57.<br />

0.39 mH<br />

8 � 8 �

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