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Chapter 14, Problem 1. Find the transfer function V o /V i of the RC circuit in Fig. 14.68. Express it using ω o = 1/RC.Figure 14.68 For Prob. 14.1. Chapter 14, Solution 1. Vo R jωRC = = H (ω) = Vi R + 1 jωC 1 + jωRC jω ω0 1 H (ω) = , where ω0 = 1 + jω ω0 RCH = H (ω) = ω ω0 1 + (ω ω0 ) 2φ = ∠H (ω) = ⎛ω⎞ π − tan -1 ⎜ ⎟ 2 ⎝ ω0 ⎠This is a highpass filter. The frequency response is the same as that for P.P.14.1 except that ω0 = 1 RC . Thus, the sketches of H and φ are shown below. H 1 0.7071
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PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 1. Find the transfer function V o /V i of the RC circuit in Fig. 14.68. Express it using oω = 1/RC.
Figure 14.68 For Prob. 14.1. Chapter 14, Solution 1.
RCj1RCj
Cj1RR
)(i
o
ω+ω
=ω+
==ωVV
H
=ω)(H0
0
j1j
ωω+ωω
, where RC1
0 =ω
20
0
)(1)(H
ωω+
ωω=ω= H ⎟
⎠
⎞⎜⎝
⎛
ωω
−π
=ω∠=φ0
1-tan2
)(H
This is a highpass filter. The frequency response is the same as that for P.P.14.1 except that RC10 =ω . Thus, the sketches of H and φ are shown below.
0
90°
45°
ω0 = 1/RC ω
φ
0
1 0.7071
ω0 = 1/RC ω
H
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 2. Obtain the transfer function V o (s)/V i of the circuit in Fig. 14.69.
Figure 14.69 For Prob. 14.2.
Chapter 14, Solution 2.
6667.0s4s
61
s/812s/82
8/s12010
8/s12
VV
)s(Hi
o+
+=
++
=++
+==
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 3. For the circuit shown in Fig. 14.70, find H(s) = V o /V i (s).
Figure 14.70 For Prob. 14.3.
Chapter 14, Solution 3. 1 1 50.2
(0.2)F
j C s sω⎯⎯→ = =
1 100.1(0.1)
Fs s
⎯⎯→ =
The circuit becomes that shown below.
Let
10 5 10 1(5 ) 5( )10 5 10( 1)//(5 ) 15 5 ( 3)5 (3 )
sss s s sZ
s s s sss s
++ +
= + = = =++ +
1 2 iZV V
Z=
+
1 15
5 5 / 1 1 2o is s ZV V V V
s s s Z= = = •
+ + + +
2
10( 1)10 5( 3)( ) 10( 1)1 2 ( 3) 10( 1) 8 52
( 3)
o
i
ss s ss sVH s V ss s s s s s
s s
++= = • = =++ + + + + +++
2
+ _ 5 10
s Vi
+
_
Vo
V1
5s
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 4. Find the transfer function H(ω ) = V O /V i of the circuits shown in Fig. 14.71.
Figure 14.71 For Prob. 14.4. Chapter 14, Solution 4.
(a) RCj1
RCj
1||R
ω+=
ω
)RCj1(LjRR
RCj1R
Lj
RCj1R
)(i
o
ω+ω+=
ω++ω
ω+==ω
VV
H
=ω)(HLjRRLC-
R2 ω++ω
(b) )LjR(Cj1
)LjR(CjCj1LjR
LjR)(
ω+ω+ω+ω
=ω+ω+
ω+=ωH
=ω)(HRCjLC1
RCjLC-2
2
ω+ω−ω+ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 5. For each of the circuits shown in Fig. 14.72, find H(s) = V o (s)/V s (s).
Figure 14.72 For Prob. 14.5. Chapter 14, Solution 5.
(a) Let // sRLZ R sLR sL
= =+
o ss
ZV VZ R
=+
( )( )
o
s s s ss
sRLV Z sRLR sLH s sRLV Z R RR s R R LR
R sL
+= = = =+ + ++
+
(b) Let
11// 1 1
Rx RsCZ RsC sRCR
sC
= = =++
o sZV V
Z sL=
+
RsLLRCsR
sRC1RsL
sRC1R
sLZZ
VV
)s(H 2i
o
++=
++
+=+
==
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 6. For the circuit shown in Fig. 14.73, find H(s) = I o (s)/I s (s).
Figure 14.73 For Prob. 14.6.
Chapter 14, Solution 6. 1H j L sL sω⎯⎯→ = =
Let //11
sZ ss
= =+
We convert the current source to a voltage source as shown below.
2 21( 1)
1 ( 1) 3 111
s so s s
ssI sIZ sV I x IsZ s s s s ss
s
+= = = =+ + + + + ++ +
+
21 3 1o s
oV sII
s s= =
+ +
2( )3 1
o
s
I sH sI s s
= =+ +
+
_ Vo Is ⋅ 1 Z
1 S
+ _
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 7.
Calculate )(ωH if H dB equals
(a) 0.05dB (b) -6.2 dB (c) 104.7 dB Chapter 14, Solution 7.
(a) Hlog2005.0 10= Hlog105.2 10
-3 =×
== × -3105.210H 005773.1
(b) Hlog206.2- 10= Hlog0.31- 10=
== -0.3110H 4898.0
(c) Hlog207.104 10= Hlog235.5 10=
== 235.510H 510718.1 × Chapter 14, Problem 8. Determine the magnitude (in dB) and the phase (in degrees) of H(ω ) = at ω = 1 if H ( )ω equals
(a) 0.05 dB (b) 125 (c) ωωj
j+2
10 (d) ωj+1
3 + ωj+2
6
Chapter 14, Solution 8. (a) 05.0H =
== 05.0log20H 10dB 26.02- , =φ °0
(b) 125H = == 125log20H 10dB 41.94 , =φ °0
(c) °∠=+
= 43.63472.4j2
10j)1(H
== 472.4log20H 10dB 01.13 , =φ °43.63
(d) °∠=−=+
++
= 34.7-743.47.2j9.3j2
6j1
3)1(H
== 743.4log20H 10dB 13.521, =φ –34.7˚
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 9. A ladder network has a voltage gain of
H(ω ) = )10)(1(
10ωω jj ++
Sketch the Bode plots for the gain. Chapter 14, Solution 9.
)10j1)(j1(1
)(ω+ω+
=ωH
10/j1log20j1log20-H 1010dB ω+−ω+=
)10/(tan)(tan- -1-1 ω−ω=φ
The magnitude and phase plots are shown below.
HdB
0.1
-40
ω1001 10
-20 10/j11
log20 10 ω+
ω+ j11
log20 10
φ
-135°
-45° ω1001 10 0.1
-180°
-90° 10/j1
1arg
ω+
ω+ j11
arg
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 10. Sketch the Bode magnitude and phase plots of:
H(jω ) = )5(
50ωω jj +
Chapter 14, Solution 10.
⎟⎠⎞
⎜⎝⎛ ω+ω
=ω+ω
=ω
5j1j1
10)j5(j
50)j(H
φ
-135°
-45° ω 100
1
10 0.1
-180°
-90° 5/j1
1argω+
ωj1arg
HdB
-20
20
ω 1001
10
0.1
-40
40
20 log1
⎟⎟⎠
⎞⎜⎜⎝
⎛
ωj1log20
⎟⎟⎟⎟
⎠
⎞
⎜⎜⎜⎜
⎝
⎛
ω+
5j1
1log20
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 11. Sketch the Bode plots for
H(ω ) = )2(
10ωωωjj
j++
Chapter 14, Solution 11.
)2j1(j)10j1(5
)(ω+ωω+
=ωH
2j1log20jlog2010j1log205log20H 10101010dB ω+−ω−ω++=
2tan10tan90- -1-1 ω−ω+°=φ
The magnitude and phase plots are shown below.
φ
-45°
45°
ω1001 10 0.1
-90°
90°
HdB
-20
20
ω1001 10 0.1
-40
40 34
14
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Chapter 14, Problem 12. A transfer function is given by
T(s) = )10(
1++
sss
Sketch the magnitude and phase Bode plots.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Solution 12.
201.0log20,)10/1(
)1(1.0)( −=++
=ωωω
jjjwT
The plots are shown below. |T| (db) 20 0 ω 0.1 1 10 100 -20 -40 arg T 90o
0 ω 0.1 1 10 100 -90o
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 13. Construct the Bode plots for
G(s) = )10(
12 +
+sss , s=jω
Chapter 14, Solution 13.
)10j1()j()j1)(101(
)j10()j(j1
)( 22 ω+ωω+
=ω+ω
ω+=ωG
10j1log20jlog40j1log2020-G 101010dB ω+−ω−ω++=
10tantan-180 -1-1 ω−ω+°=φ The magnitude and phase plots are shown below.
φ
-90°
90°
ω1001 10 0.1
-180°
GdB
-20
20
ω1001 10 0.1
-40
40
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 14. Draw the Bode plots for
H(ω ) = )2510(
)1(502 ++−
+ωωω
ωjj
j
Chapter 14, Solution 14.
⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠⎞
⎜⎝⎛ ω
+ω
+ω
ω+=ω 2
5j
2510j
1j
j12550
)(H
ω−ω++= jlog20j1log202log20H 101010dB
2
10 )5j(52j1log20 ω+ω+−
⎟⎠
⎞⎜⎝
⎛
ω−ω
−ω+°=φ51
2510tantan90- 2
1-1-
The magnitude and phase plots are shown below.
φ
-90°
90°
ω1001 10 0.1
-180°
HdB
-20
20
ω1001 10 0.1
-40
40
6
26
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 15. Construct the Bode magnitude and phase plots for
H(s) = )10)(2(
)1(40+++ss
s , s=jω
Chapter 14, Solution 15.
)10j1)(2j1()j1(2
)j10)(j2()j1(40
)(ω+ω+
ω+=
ω+ω+ω+
=ωH
10j1log202j1log20j1log202log20H 10101010dB ω+−ω+−ω++=
10tan2tantan -1-1-1 ω−ω−ω=φ
The magnitude and phase plots are shown below.
φ
-45°
45°
ω1001 10 0.1
-90°
90°
HdB
-20
20
ω1001 10 0.1
-40
40
6
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 16. Sketch Bode magnitude and phase plots for
H(s) = )16(
102 ++ sss
, s=jω
Chapter 14, Solution 16.
2 2
10 /16 0.625( )1 1
4 4
Hj jj j j j
ωω ωω ω ω ω
= =⎡ ⎤ ⎡ ⎤⎛ ⎞ ⎛ ⎞+ + + +⎢ ⎥ ⎢ ⎥⎜ ⎟ ⎜ ⎟
⎝ ⎠ ⎝ ⎠⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦
2
20 log 0.625 20log | | 20log |1 |4dBjH j j ωω ω ⎛ ⎞= − − + + ⎜ ⎟
⎝ ⎠
(20log0,625= –4.082) The magnitude and phase plots are shown below. H
φ
1
0.1
4 100ω
20 log (jω)
20 log 2
14jj ωω ⎛ ⎞+ + ⎜ ⎟
⎝ ⎠
20
10
–20
–60
40
ω0.4 1 4 10 40 100
-90
-180
90°
-tan-1 2
11 6
ωω
−
–40
–4.082
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 17. Sketch the Bode plots for
G(s) = )1()2( 2 +++ ss
s , s=jω
Chapter 14, Solution 17.
2)2j1)(j1(j)41(
)(ω+ω+ω
=ωG
2j1log40j1log20jlog204-20logG 10101010dB ω+−ω+−ω+=
2tan2tan--90 -1-1 ω−ω°=φ
The magnitude and phase plots are shown below.
φ
-90°
90°
ω1001 10 0.1
-180°
GdB
-20
20
ω
1001 10 0.1
-40
-12
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 18.
A linear network has this transfer function
H(s) = )5148(
4723
2
+++++
sssss , s=jω
Use MATLAB or equivalent to plot the magnitude and phase (in degrees) of the transfer function. Take 0.1 < ω < 10 rads/s.
Chapter 14, Solution 18. The MATLAB code is shown below.
>> w=logspace(-1,1,200); >> s=i*w; >> h=(7*s.^2+s+4)./(s.^3+8*s.^2+14*s+5); >> Phase=unwrap(angle(h))*57.23; >> semilogx(w,Phase) >> grid on
1 0 - 1 1 0 0 1 0 1- 6 0
- 4 0
- 2 0
0
2 0
4 0
6 0
w
H(jw
) Pha
se
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Now for the magnitude, we need to add the following to the above,
>> H=abs(h); >> HdB=20*log10(H); >> semilogx(w,HdB); >> grid on
1 0 - 1 1 0 0 1 0 1- 2 5
- 2 0
- 1 5
- 1 0
- 5
0
w
HdB
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 19. Sketch the asymptotic Bode plots of the magnitude and phase for
H(s) = )40)(20)(10(
100+++ sss
s , s=jω
Chapter 14, Solution 19. 100 / 80( )
( 10)( 20)( 40) (1 )(1 )(1 )10 20 40
j jH j j jj j jω ωω ω ω ωω ω ω
= =+ + + + + +
20 log(1/ 80) 20log | /1| 20 log |1 | 20 log |1 | 20 log |1 |10 20 40dBj j jH j ω ω ωω= + − + − + − +
(20log(1/80) = -38.06) The magnitude and phase plots are shown below. φ
-90
1 0.1
H
10 20 40 100
ω
20
40
0.1
60
90
20 log 180
20 log 110jω
+
20 log jω
1 2 4 10 20 40 100 200 400
ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 20. Sketch the magnitude Bode plot for the transfer function
H(ω ) = )40()5)(1(
102 +++ ωωω
ωjjj
j
Chapter 14, Solution 20.
2 2
10 /100( )(25)(40)(1 )(1 / 5) (1 / 40) (1 )(1 / 5) (1 / 40)
j jHj j j j j j
ω ωωω ω ω ω ω ω
= =+ + + + + +
20log(1/100) = -40
The magnitude plot is shown below.
1 0.1 5 10 50 100
ω
40
20 log 1100
20 log 21
15jω⎛ ⎞+⎜ ⎟
⎝ ⎠
20 log jω
20
-40
-20
-60
20 log 11 jω+
20 log 1
11 0jω
+
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 21. Sketch the magnitude Bode plot for
H(s) = )400()60)(1(
)20(2 =++
+sss
ss , s=jω
Chapter 14, Solution 21.
22
( 20) 20 (1 / 20)( )( 1)( 60 400)
400( 1)(1 60 / 400 )20
j j j jHj j jj j
ω ω ω ωωω ω ω ωω ω
+ += =
+ − + + ⎛ ⎞+ + + ⎜ ⎟⎝ ⎠
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛⎟⎠⎞
⎜⎝⎛ ω
+ω
+ω+
ω+ω=ω
2
20j
40j61)j1(
)20/j1(j05.0)(H
2
dB 20j
406j1log20j1log20
20j1log20jlog20)05.0log(20H ⎟
⎠⎞
⎜⎝⎛ ω
+ω
+−ω+−ω
++ω+=
The magnitude plot is as sketched below.
1 0.1
H&B
10 100
ω
20
20 log 0.05
20 log |1+jω/20|
–20 log 1 jω+
40
–40
–60
–80
–20 log 261
40 20j jω ω⎛ ⎞+ + ⎜ ⎟
⎝ ⎠
20
–20
20log|jω|
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 22. Find the transfer function H(ω ) with the Bode magnitude plot shown in Fig. 14.74.
Figure 14.74 For Prob. 14.22. Chapter 14, Solution 22. 10kklog2020 10 =⎯→⎯=
A zero of slope dec/dB20+ at 2j12 ω+⎯→⎯=ω
A pole of slope dec/dB20- at 20j1
120
ω+⎯→⎯=ω
A pole of slope dec/dB20- at 100j1
1100
ω+⎯→⎯=ω
Hence,
)100j1)(20j1()2j1(10
)(ω+ω+
ω+=ωH
=ω)(H)j100)(j20(
)j2(104
ω+ω+ω+
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 23. The Bode magnitude plot of H(ω ) is shown in Fig. 14.75. Find H(ω ).
Figure 14.75 For Prob. 14.23. Chapter 14, Solution 23.
A zero of slope dec/dB20+ at the origin ω⎯→⎯ j
A pole of slope dec/dB20- at 1j1
11
ω+⎯→⎯=ω
A pole of slope dec/dB40- at 2)10j1(1
10ω+
⎯→⎯=ω
Hence,
2)10j1)(j1(j
)(ω+ω+
ω=ωH
=ω)(H 2)j10)(j1(j100
ω+ω+ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 24. The magnitude plot in Fig. 14.76 represents the transfer function of a preamplifier. Find H(s).
Figure 14.76 For Prob. 14.24.
Chapter 14, Solution 24. 1040 20log 100K K= ⎯⎯→ = There is a pole at ω=50 giving 1/(1+jω/50) There is a zero at ω=500 giving (1 + jω/500). There is another pole at ω=2122 giving 1/(1 + jω/2122). Thus,
140 ( 500)40(1 / 500) 500( ) 1 1(1 / 50)(1 / 2122) ( 50)( 2122)50 2122
x sjHj j x s s
ωωω ω
++= =
+ + + +
or
8488( 500)( )( 50)( 2122)
sH ss s
+=
+ +
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 25. A series RLC network has R = 2 kΩ , L = 40 mH, and C = 1 µ F. Calculate the impedance at resonance and at one-fourth, one-half, twice, and four times the resonant frequency.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Solution 25.
s/krad5)101)(1040(
1LC1
6-3-0 =××
==ω
==ω R)( 0Z Ωk2
⎟⎠
⎞⎜⎝
⎛
ω−
ω+=ω
C4
L4
jR)4(0
00Z
⎟⎠
⎞⎜⎝
⎛××
−×⋅×
+=ω)101)(105(
41040
4105
j2000)4( 6-33-
3
0Z
)5400050(j2000)4( 0 −+=ωZ
=ω )4( 0Z Ω− k75.0j2
⎟⎠
⎞⎜⎝
⎛
ω−
ω+=ω
C2
L2
jR)2(0
00Z
⎟⎠
⎞⎜⎝
⎛××
−××
+=ω)101)(105(
2)1040(
2)105(
j2000)2( 6-33-
3
0Z
Z(ω0/2) = 200+j(100-2000/5)
=ω )2( 0Z Ω− k3.0j2
⎟⎠
⎞⎜⎝
⎛
ω−ω+=ω
C21
L2jR)2(0
00Z
⎟⎠
⎞⎜⎝
⎛××
−××+=ω)101)(105)(2(
1)1040)(105)(2(j2000)2( 6-3
3-30Z
=ω )2( 0Z Ω+ k3.0j2
⎟⎠
⎞⎜⎝
⎛
ω−ω+=ω
C41
L4jR)4(0
00Z
⎟⎠
⎞⎜⎝
⎛××
−××+=ω)101)(105)(4(
1)1040)(105)(4(j2000)4( 6-3
3-30Z
=ω )4( 0Z Ω+ k75.0j2
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 26. A coil with resistance 3Ω and inductance 100 mH is connected in series with a capacitor of 50 pF, a resistor of 6Ω and a signal generator that gives 110 V rms at all frequencies. Calculate oω , Q, and B at resonance of the resultant series RLC circuit.
Chapter 14, Solution 26. Consider the circuit as shown below. This is a series RLC resonant circuit. R = 6 + 3 = 9 Ω
3 12
1 1 447.21 krad/s100 10 50 10
o LC x x xω
− −= = =
3 3447.21 10 100 10 49699
oL x x xQR
ω= = =
3447.21 10 90 rad/s
4969o xB
Qω
= = =
+ _ 100 mH
6 Ω 50 µF 3 Ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 27.
Design a series RLC resonant circuit with oω = 40 rad/s and B = 10 rad/s.
Chapter 14, Solution 27.
2
1 14040o LC
LCω = = ⎯⎯→ =
10 10RB R LL
= = ⎯⎯→ =
If we select R =1 Ω, then L = R/10 = 0.1 H and
2 2
1 1 6.25 mF40 40 0.1
CL x
= = =
Chapter 14, Problem 28. Design a series RLC circuit with B = 20 rad/s and oω = 1,000 rad/s. Find the circuit’s Q. Let R = 10 Ω . Chapter 14, Solution 28. Let Ω= 10R .
H5.02010
BR
L ===
F2)5.0()1000(
1L
1C 22
0µ==
ω=
5020
1000B
Q 0 ==ω
=
Therefore, if Ω= 10R then =L H5.0 , =C F2 µ , =Q 50
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 29. Let v s = 20 cos(at) V in the circuit of Fig. 14.77. Find oω , Q, and B, as seen by the capacitor.
Figure 14.77 For Prob. 14.29.
Chapter 14, Solution 29. We convert the voltage source to a current source as shown below.
20 cos12si tω= , R = 12//45= 12x45/57 = 9.4737 kΩ
3 6
1 1 4.082 krad/s60 10 1 10
o LC x x xω
− −= = =
3 6
1 1 105.55 rad/s9.4737 10 10
BRC x x −= = =
4082 38.674105.55
oQBω
= = = = 38.67
12 k 60 mH 1 µF is 45 k
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 30. A circuit consisting of a coil with inductance 10 mH and resistance 20 Ω is connected in series with a capacitor and a generator with an rms voltage of 120 V. Find: (a) the value of the capacitance that will cause the circuit to be in resonance at 15 kHz (b) the current through the coil at resonance (c) the Q of the circuit Chapter 14, Solution 30. Select Ω= 10R .
mH50H05.0)20)(10(
10Q
RL0
===ω
=
F2.0)05.0)(100(
1L
1C 2
0==
ω=
s/rad5.0)2.0)(10(
1RC1
B ===
Therefore, if Ω= 10R then =L 50 mH, =C F2.0 , =B s/rad5.0
Chapter 14, Problem 31.
Design a parallel resonant RLC circuit with oω = 10rad/s and Q = 20. Calculate the bandwidth of the circuit. Let R = 10Ω . Chapter 14, Solution 31.
ω=⎯→⎯ω= L
LX
LLX
rad/s 10x796.810x40
10x6.5x10x10x2X
RLRB 6
3
36
L=
π=
ω==
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 32. A parallel RLC circuit has the following values:
R = 60 Ω , L = 1 mH, and C = 50 Fµ .
Find the quality factor, the resonant frequency, and the bandwidth of the RLC circuit. Chapter 14, Solution 32.
3 6
1 1 4.472 krad/s10 50 10
o LC x xω
− −= = =
6
1 1 333.33 rad/s60 50 10
BRC x x −= = =
4472 13.42333.33
oQBω
= = =
Chapter 14, Problem 33.
A parallel resonant circuit with quality factor 120 has a resonant frequency of 6 × 10 6 rad/s. Calculate the bandwidth and half-power frequencies. Chapter 14, Solution 33.
pF 84.5610x40x10x6.5x2
80Rf2
QCRCQ36o
o =π
=π
=⎯→⎯ω=
80x10x6.5x210x40
Qf2RL
LRQ 6
3
oo π=
π=⎯→⎯
ω= = 14.21 µH
Chapter 14, Problem 34. A parallel RLC circuit is resonant at 5.6 MHz, has a Q of 80, and has a resistive branch of 40 kΩ . Determine the values of L and C in the other two branches. Chapter 14, Solution 34.
(a) krad/s 443.110x60x10x8
1LC1
63o ===ω−−
(b) rad/s 33.310x60x10x5
1RC1B
63===
−
(c) 9.43210x60x10x5x10x443.1RCQ 633
o ==ω= −
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 35. A parallel RLC circuit has R = 5kΩ , L = 8 mH, and C = Fµ . Determine:
(a) the resonant frequency (b) the bandwidth (c) the quality factor Chapter 14, Solution 35. At resonance,
=×
==⎯→⎯= 3-10251
Y1
RR1
Y Ω40
=×
=ω
=⎯→⎯ω=)40)(10200(
80R
QCRCQ 3
00 F10 µ
=××
=ω
=⎯→⎯=ω)1010)(104(
1C
1L
LC1
6-1020
0 H5.2 µ
=×
=ω
=80
10200Q
B3
0 s/krad5.2
=−=−ω=ω 25.12002B
01 198.75 krad/s
=+=+ω=ω 25.12002B
02 201.25 krad/s
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 36. It is expected that a parallel RLC resonant circuit has a midband admittance of 25 × 110 3− S, quality factor of 80, and a resonant frequency of 200 krad/s. Calculate the values of R, L, and C. Find the bandwidth and the half-power frequencies. Chapter 14, Solution 36.
s/rad5000LC1
0 ==ω
==ω⎯→⎯=ω R)(R1
)( 00 ZY Ωk2
mS75.18j5.0L
4C4
jR1)4(
0
00 −=⎟⎟
⎠
⎞⎜⎜⎝
⎛ω
−ω
+=ωY
=−
=ω01875.0j0005.0
1)4( 0Z Ω+ 3.53j4212.1
mS5.7j5.0L
2C2
jR1)2(
0
00 −=⎟⎟
⎠
⎞⎜⎜⎝
⎛ω
−ω
+=ωY
=−
=ω0075.0j0005.0
1)2( 0Z Ω+ 74.132j85.8
mS5.7j5.0C2
1L2jR1)2(
000 +=⎟⎟
⎠
⎞⎜⎜⎝
⎛ω
−ω+=ωY
=ω )2( 0Z Ω− 74.132j85.8
mS75.18j5.0C4
1L4jR1)4(
000 +=⎟⎟
⎠
⎞⎜⎜⎝
⎛ω
−ω+=ωY
=ω )4( 0Z Ω− 3.53j4212.1
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 37. Rework Prob. 14.25 if the elements are connected in parallel. Chapter 14, Solution 37.
22 )C
1L(R
)C
1L(jRLRjCL
LjCj
1R
)Cj
1R(Lj)
Cj1R//(LjZ
ω−ω+
⎟⎠⎞
⎜⎝⎛
ω−ω−⎟
⎠⎞
⎜⎝⎛ ω+
=ω+
ω+
ω+ω
=ω
+ω=
1)CRLC(0)
C1L(R
C1L
CLLR
)ZIm( 22222
2
=−ω⎯→⎯=
ω−ω+
⎟⎠⎞
⎜⎝⎛
ω−ω−ω
=
Thus,
22CRLC
1
−=ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 38. Find the resonant frequency of the circuit in Fig. 14.78.
Figure 14.78 For Prob. 14.38. Chapter 14, Solution 38.
222 LR
LjRCjCjLjR
1Yω+
ω−+ω=ω+
ω+=
At resonance, 0)Im( =Y , i.e.
0LR
LC 22
02
00 =
ω+ω
−ω
CL
LR 220
2 =ω+
2
-36--32
20
104050
)101)(1040(1
LR
LC1
⎟⎟⎠
⎞⎜⎜⎝
⎛
×−
××=−=ω
=ω0 s/rad4841
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 39. For the “tank” circuit in Fig. 14.79, find the resonant frequency.
Figure 14.79 For Probs. 14.39 and 14.91. Chapter 14, Solution 39. (a) s/krad810x)8690(2)ff(2B 3
1212 π=−π=−π=ω−ω=
3321o 10X17610x)88(2)(
21
π=π=ω+ω=ω
nF89.1910x2x10x8
1BR1C
RC1B 33 =
π==⎯→⎯=
(b) 923o
2o10x89.19x)10X176(
1C
1LLC1
−π=
ω=⎯→⎯=ω = 164.45 µH
(c ) s/krad9.552176o =π=ω (d) s/krad13.258B =π=
(e) 228
176B
Q o =ππ
=ω
=
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 40. A parallel resonance circuit has a resistance of 2 kΩ and half-power frequencies of 86 kHz and 90 kHz. Determine: (a) the capacitance (b) the inductance (c) the resonant frequency (d) the bandwidth (e) the quality factor Chapter 14, Solution 40. (a) L = 5 + 10 = 15 mH
===ω−− 630
10x20x10x15
1LC1 1.8257 k rad/sec
==ω= −633
0 10x20x10x25x10x8257.1RCQ 912.8
===−63 10x2010x25
1RC1B 2 rad/s
(b) To increase B by 100% means that B’ = 4.
==′
=′4x10x25
1BR1C 3 10 µF
Since F10CC
CCC21
21 µ=+
=′ and C1 = 20 µF, we then obtain C2 = 20 µF.
Therefore, to increase the bandwidth, we merely add another 20 µF in series with the first one.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 41. For the circuit shown in Fig. 14.80, next page: (a) Calculate the resonant frequency oω , the quality factor Q, and the bandwidth B. (b) What value of capacitance must be connected in series with the 20- Fµ capacitor in order to double the bandwidth?
Figure 14.80 For Prob. 14.41. Chapter 14, Solution 41.
(a) This is a series RLC circuit. Ω=+= 862R , H1L = , F4.0C =
===ω4.0
1LC1
0 s/rad5811.1
==ω
=8
5811.1R
LQ 0 1976.0
==LR
B s/rad8
(b) This is a parallel RLC circuit.
F263)6)(3(
F6andF3 µ=+
⎯→⎯µµ
F2C µ= , Ω= k2R , mH20L =
=××
==ω)1020)(102(
1LC1
3-6-0 s/krad5
=××
×=
ω=
)1020)(105(102
LR
Q 3-3
3
020
=××
==)102)(102(
1RC1
B 6-3 250 rad/s
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 42. For the circuits in Fig. 14.81, find the resonant frequency oω , the quality factor Q, and the bandwidth B.
Figure 14.81 For Prob. 14.42.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Solution 42.
(a) )LjR(||)Cj1(in ω+ω=Z
RCjLC1LjR
Cj1
LjR
CjLjR
2in ω+ω−ω+
=
ω+ω+
ωω+
=Z
22222
2
in CR)LC1()RCjLC1)(LjR(
ω+ω−ω−ω−ω+
=Z
At resonance, 0)Im( in =Z , i.e.
CR)LC1(L0 20
200 ω−ω−ω=
CRLCL 2220 −=ω
=−
=ωCL
CRL2
20 2
2
LR
LC1
−
(b) )Cj1Lj(||Rin ω+ω=Z
RCj)LC1()LC1(R
Cj1LjR)Cj1Lj(R
2
2
in ω+ω−ω−
=ω+ω+ω+ω
=Z
22222
22
in CR)LC1(]RCj)LC1)[(LC1(R
ω+ω−ω−ω−ω−
=Z
At resonance, 0)Im( in =Z , i.e.
RC)LC1(R0 2 ωω−= 0LC1 2 =ω−
=ω0 LC1
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 43. Calculate the resonant frequency of each of the circuits in Fig. 14.82.
Figure 14.82 For Prob. 14.43. Chapter 14, Solution 43. Consider the circuit below.
(a) )Cj1R(||)Lj||R( 21in ω+ω=Z
⎟⎠
⎞⎜⎝
⎛ω
+⎟⎠
⎞⎜⎝
⎛
ω+ω
=Cj
1R||
LjRLjR
21
1inZ
LjRLjR
Cj1
R
Cj1
RLjR
LRj
1
12
21
1
in
ω+ω
+ω
+
⎟⎠
⎞⎜⎝
⎛ω
+⋅ω+
ω
=Z
12
21
21in LCR)CRj1)(LjR(
)CRj1(LRjω−ω+ω+
ω+ω=Z
)CRRL(jLCRLCRRLRjLCRR-
2122
12
1
1212
in +ω+ω−ω−ω+ω
=Z
221
222
21
21
2122
12
11212
in )CRRL()LCRLCRR()]CRRL(jLCRLCRR)[LRjLCRR-(
+ω+ω−ω−+ω−ω−ω−ω+ω
=Z
R2 jωL
1/jωC
Zin R1
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
At resonance, 0)Im( in =Z , i.e. )LCRLCRR(LR)CRRL(LCRR0 2
21
2112121
3 ω−ω−ω++ω= CLRLRLCRR0 22
132
122
221
3 ω−ω+ω= LC1CR0 222
22 ω−+ω=
1)CRLC( 222
2 =−ω
222
0 CRLC1−
=ω
26-26-0 )109()1.0()109)(02.0(1
×−×=ω
=ω0 s/krad357.2 (b) At s/krad357.20 =ω=ω ,
14.47j)1020)(10357.2(jLj -33 =××=ω
0212.0j9996.014.47j1
14.47jLj||R1 +=
+=ω
14.47j1.0)109)(10357.2(j
11.0
Cj1
R 6-32 −=××
+=ω
+
)Cj1R(||)Lj||R()( 210in ω+ω=ωZ
)14.47j1.0()0212.0j9996.0()14.47j1.0)(0212.0j9996.0(
)( 0in −++−+
=ωZ
=ω )( 0inZ Ω1
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 44. * For the circuit in Fig. 14.83, find: (a) the resonant frequency oω
(b) Z in ( oω )
Figure 14.83 For Prob. 14.44. * An asterisk indicates a challenging problem. Chapter 14, Solution 44. We find the input impedance of the circuit shown below.
Cj111
j2j
31ω+
+ω+ω
=Z
, 1=ω
2
2
C1jCC
-j0.5jC1
jCj-j1.5
1++
+=+
++=Z
)t(v and )t(i are in phase when Z is purely real, i.e.
1)1C(C1
C-0.50 2
2 =−⎯→⎯+
+= or =C F1
Ω=⎯→⎯=+
= 221
C1C1
2
2
ZZ
20)10)(2( === IZV
V)tsin(20)t(v = , i.e. =oV V20
Z 1
jω(2/3)
1/jωC
1/jω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 45. For the circuit shown in Fig. 14.84, find oω , B, and Q, as seen by the voltage across the inductor.
Figure 14.84 For Prob. 14.45.
Chapter 14, Solution 45. Convert the voltage source to a current source as shown below. R = 30//50 = 30x50/80 = 18.75 kΩ This is a parallel resonant circuit.
3 6
1 1 447.21 rad/s10 10 50 10
o LC x x xω
− −= = =
3 6
1 1 1.067 rad/s18.75 10 50 10
BRC x x x −= = =
447.21 419.131.067
oQBω
= = =
Is 10 mH 50 µF 50 kΩ30 kΩ
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 46. For the network illustrated in Fig. 14.85, find (a) the transfer function H(ω ) = V o (ω )/I(ω ),
(b) the magnitude of H at oω = 1 rad/s.
Figure 14.85 For Probs. 14.46, 14.78, and 14.92. Chapter 14, Solution 46. (a) This is an RLC series circuit.
nF26.1110x10x)10x15x2(
1L
1CLC1
323o
2o =π
=ω
=⎯→⎯=ω−
(b) Z = R, I = V/Z = 120/20 = 6 A
(c ) 12.471520
10x10x10x15x2R
LQ
33o =π=
π=
ω=
−
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 47. Show that a series LR circuit is a lowpass filter if the output is taken across the resistor. Calculate the corner frequency f c if L = 2 mH and R = 10 kΩ . Chapter 14, Solution 47.
RLj1
1LjR
R)(
i
o
ω+=
ω+==ω
VV
H
1)0(H = and 0)(H =∞ showing that this circuit is a lowpass filter.
At the corner frequency, 2
1)(H c =ω , i.e.
RL
1
RL
1
12
1 c
2c
ω=⎯→⎯
⎟⎠⎞
⎜⎝⎛ω
+
= or LR
c =ω
Hence,
cc f2LR
π==ω
=××
⋅π
=⋅π
= 3-
3
c 1021010
21
LR
21
f kHz796
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 48. Find the transfer function V o /V s of the circuit in Fig. 14.86. Show that the circuit is a lowpass filter.
Figure 14.86 For Prob. 14.48. Chapter 14, Solution 48.
Cj1
||RLj
Cj1
||R)(
ω+ω
ω=ωH
Cj1RCjR
Lj
Cj1RCjR
)(
ω+ω
+ω
ω+ω
=ωH
=ω)(HRLCLjR
R2ω−ω+
1)0(H = and 0)(H =∞ showing that this circuit is a lowpass filter.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 49. Determine the cutoff frequency of the lowpass filter described by
H(ω ) = 102
4ωj+
Find the gain in dB and phase of H(ω ) at ω = 2 rad/s. Chapter 14, Solution 49.
At dc, 224
)0(H == .
Hence, 2
2)0(H
21
)(H ==ω
2c1004
42
2ω+
=
2.081004 c
2c =ω⎯→⎯=ω+
10j12
20j24
)2(H+
=+
=
199.01012
)2(H ==
In dB, =)2(Hlog20 10 14.023-
== 10-tan)2(Harg -1 °84.3-
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 50. Determine what type of filter is in Fig. 14.87. Calculate the corner frequency f c .
Figure 14.87 For Prob. 14.50. Chapter 14, Solution 50.
LjR
Lj)(
i
o
ω+ω
==ωVV
H
0)0(H = and 1)(H =∞ showing that this circuit is a highpass filter.
LR
1
LR
1
12
1)(
c2
c
c ω=⎯→⎯
⎟⎠
⎞⎜⎝
⎛
ω+
==ωH
or cc f2LR
π==ω
=⋅π
=⋅π
=1.0
20021
LR
21
fc Hz3.318
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 51.
Design an RL lowpass filter that uses a 40-mH coil and has a cutoff frequency of 5 kHz. Chapter 14, Solution 51. The lowpass RL filter is shown below. L + + vs R vo - -
R/Lj11
LjRR
VV
Hs
oω+
=ω+
==
Ω=π=π=⎯→⎯π==ω − k256.110x40x10x5x2Lf2Rf2LR 33
ccc
Chapter 14, Problem 52.
In a highpass RL filter with a cutoff frequency of 100 kHz, L = 40 mH. Find R. Chapter 14, Solution 52.
cc f2LR
π==ω
=×π=π= )1040)(10)(2(Lf2R -35
c Ωk13.25
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 53.
Design a series RLC type bandpass filter with cutoff frequencies of 10 kHz and 11 kHz. Assuming C = 80 pF, find R, L, and Q. Chapter 14, Solution 53.
311 1020f2 ×π=π=ω
322 1022f2 ×π=π=ω
3
12 102B ×π=ω−ω=
3120 1021
2×π=
ω+ω=ω
=ππ
=ω
=221
BQ 0 10.5
C1
LLC1
20
0 ω=⎯→⎯=ω
=××π
=)1080()1021(
1L 12-23 H872.2
BLRLR
B =⎯→⎯=
=×π= )872.2)(102(R 3 Ωk045.18 Chapter 14, Problem 54. Design a passive bandstop filter with oω = 10 rad/s and Q = 20.
Chapter 14, Solution 54. This is an open-ended problem with several possible solutions. We may choose the bandstop filter in Fig. 14.38.
1 10 0.01o LCLC
ω = = ⎯⎯→ =
10 20 2oL LQ L RRRω
= = = ⎯⎯→ =
If we select L = 1H, then R=0.5 Ω, and C = 0.01/L = 10 mF.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 55. Determine the range of frequencies that will be passed by a series RLC bandpass filter with R = 10Ω , L = 25mH, and C = 0.4 µ F. Find the quality factor. Chapter 14, Solution 55.
s/krad10)104.0)(1025(
1LC1
63o =××
==ω−−
s/krad4.01025
10LR
B 3- =×
==
==4.0
10Q 25
s/krad8.92.0102Bo1 =−=−ω=ω or kHz56.12
8.9f1 =
π=
s/krad2.102.0102Bo2 =+=+ω=ω or kHz62.12
2.10f2 =
π=
Therefore,
kHz62.1fkHz56.1 <<
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 56. (a) Show that for a bandpass filter,
H(s) = 20
2 ω++ sBssB , s = jw
where B = bandwidth of the filter and oω is the center frequency.
(b) Similarly, show that for a bandstop filter,
H(s) = 20
2
20
2
ωω++
+sBs
s, s = jw
Chapter 14, Solution 56.
(a) From Eq 14.54,
LC1
LRss
LRs
LCssRC1sRC
sC1sLR
R)s(2
2++
=++
=++
=H
Since LR
B = and LC1
0 =ω ,
=)s(H 20
2 sBssB
ω++
(b) From Eq. 14.56,
LC1
LR
ss
LC1
s
sC1
sLR
sC1
sL)s(
2
2
++
+=
++
+=H
=)s(H 20
2
20
2
sBss
ω++ω+
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 57. Determine the center frequency and bandwidth of the bandpass filters in Fig. 14.88.
Figure 14.88 For Prob. 14.57.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Solution 57. (a) Consider the circuit below.
sC2
R
sC1
RsC1
RsC1
R||sC1
R)s(+
⎟⎠⎞
⎜⎝⎛
++=⎟
⎠⎞
⎜⎝⎛
++=Z
)sRC2(sCsRC1
R)s(+
++=Z
)sRC2(sCCRssRC31
)s(222
+++
=Z
ZV
I s=
)sRC2(RsC2sC1 s
1 +=
+=
ZV
II
222s
1o CRssRC31)sRC2(sC
sRC2R
R+++
⋅+
==V
IV
222s
o
CRssRC31sRC
)s(++
==VV
H
⎥⎥⎥
⎦
⎤
⎢⎢⎢
⎣
⎡
++=
222
CR1
sRC3
s
sRC3
31
)s(H
Thus, 2220 CR
1=ω or ==ω
RC1
0 s/rad1
==RC3
B s/rad3
1/sC R
+ −
Vs +
Vo
−
1/sC R
I1I
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(b) Similarly,
sLR2)sLR(R
sL)sLR(||RsL)s(++
+=++=Z
sLR2LssRL3R
)s(222
+++
=Z
ZV
I s= , )sLR2(
RsLR2
R s1 +
=+
=Z
VII
222s
1o LssRL3RsLR2
sLR2sLR
sL++
+⋅
+=⋅=
VIV
2
22
222s
o
LR
sLR3
s
sLR3
31
LssRL3RsRL
)s(++
⎟⎠⎞
⎜⎝⎛
=++
==VV
H
Thus, ==ωLR
0 s/rad1
==LR3
B s/rad3
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 58. The circuit parameters for a series RLC bandstop filter are R = 2 kΩ , L = 0.1 H, C = 40 pF. Calculate: (a) the center frequency (b) the half-power frequencies (c) the quality factor Chapter 14, Solution 58.
(a) =×
==ω)1040)(1.0(
1LC1
12-0 s/rad105.0 6×
(b) 43
1021.0
102LR
B ×=×
==
25102105.0
BQ 4
60 =
×
×=
ω=
As a high Q circuit,
=−=−ω=ω )150(102B 4
01 s/krad490
=+=+ω=ω )150(102B 4
02 s/krad510
(c) As seen in part (b), =Q 25
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Chapter 14, Problem 59. Find the bandwidth and center frequency of the bandstop filter of Fig. 14.89.
Figure 14.89 For Prob. 14.59. Chapter 14, Solution 59. Consider the circuit below.
sC1sLR)sC1sL(R
sC1
sL||R)s(+++
=⎟⎠⎞
⎜⎝⎛
+=Z
LCssRC1)LCs1(R
)s( 2
2
+++
=Z
R
sL
1/sC
Ro
+ −
Vi
+
Vo
−
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
LCRsRLCRsCsRRR)LCs1(R
R 2o
2oo
2
oi
o
+++++
=+
==Z
ZVV
H
LCssRC1)LCs1(R
RR 2
2
ooin +++
+=+= ZZ
LCssRC1LCRsRLCRsCsRRR
2
2o
2oo
in ++++++
=Z
ω= js
RCjLC1LCRRLCRCRRjR
2
2o
2oo
in ω+ω−ω−+ω−ω+
=Z
222
2o
2o
2o
in )RC()LC1()RCjLC1)(CRRjLCRLCRRR(
ω+ω−ω−ω−ω+ω−ω−+
=Z
0)Im( in =Z implies that
0)LC1(CRR]LCRLCRRR[RC- 2
o2
o2
o =ω−ω+ω−ω−+ω
0LCRRLCRLCRRR o2
o2
o2
o =ω+−ω−ω−+
RLCR2 =ω
=××
==ω)104)(101(
1LC1
6-3-0 s/krad811.15
LCRLCRRCRRjR)LC1(R
2o
2oo
2
ω−ω−+ω+ω−
=H
RRR
)0(HHo
max +==
or o
oo
2o
2
max RRR
)RR(LCCRRjRR
LC1Rlim)(HH
+=
+−ω
+ω+
⎟⎠⎞
⎜⎝⎛ −ω=∞=
∞→ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
At 1ω and 2ω , mzxH2
1=H
CRRj)RR(LCRR)LC1(R
)RR(2R
oo2
o
2
o ω++ω−+ω−
=+
2o
2o
2o
2o
))RR(LCRR()CRR()LC1)(RR(
21
+ω−++ω
ω−+=
28-226-
-92
)10410()10(96)1041(10
21
×⋅ω−+ω×
×⋅ω−=
21
)10410()10(96)1041(10
028-226-
-92
−×⋅ω−+ω×
×⋅ω−=
0)10410()1096()2)(10410( 2-822-6-82 =×⋅ω−+ω×−×⋅ω−
2-822-62-82 )10410()1096()10410)(2( ×⋅ω−+ω×=×⋅ω−
0)10410()1096( 2-822-6 =×⋅ω−−ω×
010010092.8106.1 2-74-15 =+ω×−ω×
01025.610058.5 1684 =×+×−ω
⎩⎨⎧
××
=ω 8
82
101471.2109109.2
Hence,
s/krad653.141 =ω
s/krad061.172 =ω
=−=ω−ω= 653.14061.17B 12 s/krad408.2
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 60. Obtain the transfer function of a highpass filter with a passband gain of 10 and a cutoff frequency of 50 rad/s. Chapter 14, Solution 60.
RC1j
jRCj1
RCj)(
+ωω
=ω+
ω=ω′H (from Eq. 14.52)
This has a unity passband gain, i.e. 1)(H =∞ .
50RC1
c =ω=
ω+ω
=ω′=ωj50
10j)(10)( HH ^
=ω)(Hω+ωj50
10j
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 61. Find the transfer function for each of the active filters in Fig. 14.90.
Figure 14.90 For Probs. 14.61 and 14.62. Chapter 14, Solution 61.
(a) iCj1RCj1
VVω+
ω=+ , oVV =−
Since −+ = VV ,
oiRCj11
VV =ω+
==ωi
o)(VV
HRCj1
1ω+
(b) iCj1RR
VVω+
=+ , oVV =−
Since −+ = VV ,
oiRCj1RCj
VV =ω+
ω
==ωi
o)(VV
HRCj1
RCjω+
ω
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 62. The filter in Fig. 14.90(b) has a 3-dB cutoff frequency at 1 kHz. If its input is connected to a 120-mV variable frequency signal, find the output voltage at: (a) 200 Hz (b) 2 kHz (c) 10 kHz Chapter 14, Solution 62. This is a highpass filter.
RCj11
RCj1RCj
)(ω−
=ω+
ω=ωH
ωω−=ω
cj11
)(H , )1000(2RC1
c π==ω
f1000j11
ffj11
)(c −
=−
=ωH
(a) i
o
5j11
)Hz200f(VV
H =−
==
=−
=5j1
mV120oV mV53.23
(b) i
o
5.0j11
)kHz2f(VV
H =−
==
=−
=5.0j1
mV120oV mV3.107
(c) i
o
1.0j11
)kHz10f(VV
H =−
==
=−
=1.0j1
mV120oV mV4.119
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 63. Design an active first-order highpass filter with
H(s) = -10
100+s
s , s = jω
Use a 1- Fµ capacitor. Chapter 14, Solution 63.
For an active highpass filter,
ii
fiRsC1
RsC)s(H+
−= (1)
But
10/s1s10)s(H
+−= (2)
Comparing (1) and (2) leads to:
Ω==⎯→⎯= M10C10R10RC
iffi
Ω==⎯→⎯= k100C
1.0R1.0RCi
iii
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 64. Obtain the transfer function of the active filter in Fig. 14.91 on the next page. What kind of filter is it?
Figure 14.91 For Prob. 14.64. Chapter 14, Solution 64.
ff
f
fff CRj1
RCj1
||RZω+
=ω
=
i
ii
iii Cj
CRj1Cj
1RZ
ωω+
=ω
+=
Hence,
===ωi
f
i
o -)(
ZZ
VV
H)CRj1)(CRj1(
CRj-
iiff
if
ω+ω+ω
This is a bandpass filter. )(ωH is similar to the product of the transfer function of a lowpass filter and a highpass filter.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 65. A highpass filter is shown in Fig. 14.92. Show that the transfer function is
H(ω ) = ⎟⎟⎠
⎞⎜⎜⎝
⎛+
i
f
RR
1RCj
RCjω
ω+1
Figure 14.92 For Prob. 14.65. Chapter 14, Solution 65.
ii RCj1RCj
Cj1RR
VVVω+
ω=
ω+=+
ofi
i
RRR
VV+
=−
Since −+ = VV ,
iofi
i
RCj1RCj
RRR
VVω+
ω=
+
==ωi
o)(VV
H ⎟⎠
⎞⎜⎝
⎛ω+
ω⎟⎠
⎞⎜⎝
⎛+
RCj1RCj
RR
1i
f
It is evident that as ∞→ω , the gain is i
f
RR
1+ and that the corner frequency is RC1
.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 66. A “general” first-order filter is shown in Fig. 14.93. (a) Show that the transfer function is
H(s) = 43
4
RRR+
× CRs
RRRRCRs
2
43211
/1]//)[/1(
+−+
s=jω (b) What condition must be satisfied for the circuit to operate as a highpass filter? (c) What condition must be satisfied for the circuit to operate as a lowpass filter?
Figure 14.93 For Prob. 14.66. Chapter 14, Solution 66.
(a) Proof
(b) When 3241 RRRR = ,
CR1ss
RRR
)s(243
4
+⋅
+=H
(c) When ∞→3R ,
CR1sCR1-
)s(2
1
+=H
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 67.
Design an active lowpass filter with dc gain of 0.25 and a corner frequency of 500 Hz. Chapter 14, Solution 67.
fii
f R4R41
RR
gain DC =⎯→⎯==
s/rad)500(2CR
1frequencyCorner
ffc π==ω=
If we select Ω= k20R f , then Ω= k80R i and
nF915.15)1020)(500)(2(
1C 3 =
×π=
Therefore, if =fR Ωk20 , then =iR Ωk80 and =C nF915.15
Chapter 14, Problem 68.
Design an active highpass filter with a high-frequency gain of 5 and a corner frequency of 200 Hz. Chapter 14, Solution 68.
ifi
f R5RRR
5gainfrequency High =⎯→⎯==
s/rad)200(2CR
1frequencyCorner
iic π==ω=
If we select Ω= k20R i , then Ω= k100R f and
nF8.39)1020)(200)(2(
1C 3 =
×π=
Therefore, if =iR Ωk20 , then =fR Ωk100 and =C nF8.39
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 69.
Design the filter in Fig. 14.94 to meet the following requirements: (a) It must attenuate a signal at 2 kHz by 3 dB compared with its value at 10 MHz.
(b) It must provide a steady-state output of v o (t) = 10 sin(2π × 10 8 t + 180 o ) V for an input v s (t) = 4sin(2π × 10 8 t) V.
Figure 14.94 For Prob. 14.69. Chapter 14, Solution 69. This is a highpass filter with 2fc = kHz.
RC1
f2 cc =π=ω
3c 104
1f2
1RC
×π=
π=
Hz108 may be regarded as high frequency. Hence the high-frequency gain is
410
RRf −
=−
or R5.2Rf =
If we let =R Ωk10 , then =fR Ωk25 , and =×π
= 41040001
C nF96.7 .
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 70.
* A second-order active filter known as a Butterworth filter is shown in Fig. 14.95. (a) Find the transfer function V o /V i .
(b) Show that it is a lowpass filter.
Figure 14.95 For Prob. 14.70. * an asterisk indicates a challenging problem. Chapter 14, Solution 70.
(a) )YYY(YYY
YY)s()s(
)s(321421
21
i
o
+++==
VV
H
where 11
1 GR1
Y == , 22
2 GR1
Y == , 13 sCY = , 24 sCY = .
=)s(H)sCGG(sCGG
GG
121221
21
+++
(b) 1GGGG
)0(H21
21 == , 0)(H =∞
showing that this circuit is a lowpass filter.
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Chapter 14, Problem 71. Use magnitude and frequency scaling on the circuit of Fig. 14.76 to obtain an equivalent circuit in which the inductor and capacitor have magnitude 1 H and 1 F respectively. Chapter 14, Solution 71. Ω= 50R , mH40L = , F1C µ=
)1040(KK
1LKK
L 3-
f
m
f
m ×⋅=⎯→⎯=′
mf KK25 = (1)
fm
-6
fm KK10
1KK
CC =⎯→⎯=′
mf
6
K1
K10 = (2)
Substituting (1) into (2),
ff
6
K251
K10 =
=fK -3102.0 ×
== fm K25K -3105×
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Chapter 14, Problem 72. What values of K m and K f will scale a 4-mH inductor and a 20-µ F capacitor to 1 H and 2 F respectively? Chapter 14, Solution 72.
CLLC
KKLC
CL 2f2
f ′′=⎯→⎯=′′
8-
-6-32f 104
)2)(1()1020)(104(
K ×=××
=
=fK -4102×
LC
CL
KKCL
CL 2
m2m ⋅
′′
=⎯→⎯=′′
3-
3-
-62m 105.2
)104)(2()1020)(1(
K ×=××
=
=mK -2105×
Chapter 14, Problem 73. Calculate the values of R, L, and C that will result in R = 12kΩ , L = 40 µ H and C = 300 nF respectively when magnitude-scaled by 800 and frequency-scaled by 1000. Chapter 14, Solution 73.
=×==′ )10800)(12(RKR 3m ΩM6.9
=×==′ )1040(1000800
LKK
L 6-
f
m F32 µ
=×
==′ )1000)(800(10300
KKC
C-9
fmpF375.0
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 74. A circuit has R 1 = 3 Ω , R 2 = 10Ω , L = 2H and C = 1/10F. After the circuit is magnitude-scaled by 100 and frequency-scaled by 10 6 , find the new values of the circuit elements. Chapter 14, Solution 74.
Ω=== 300100x3RK'R 1m1
Ω=== k 1100x10RK'R 2m2
H 200)2(1010L
KK'L 6
2
f
m µ===
nF 110101
KKC'C 8fm
===
Chapter 14, Problem 75. In an RLC circuit, R = 20Ω , L = 4 H and C = 1 F. The circuit is magnitude-scaled by 10 and frequency-scaled by 10 5 . Calculate the new values of the elements. Chapter 14, Solution 75.
Ω=== 20010x20RK'R m
H 400)4(1010L
KK
'L5f
m µ===
F 110x101
KKC'C
5fmµ===
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Chapter 14, Problem 76. Given a parallel RLC circuit with R = 5 kΩ , L = 10 mH, and C = 20 µ F, if the circuit is magnitude-scaled by K m = 500 and frequency-scaled by K f = 10 5 , find the resulting values of R, L, and C.
Chapter 14, Solution 76. 3' 500 5 10 25 MmR K R x x= = = Ω
5
500' (10 ) 50 H10
m
f
KL L mHK
µ= = =
6
5
20 10' 0.4 pF500 10m f
C xCK K x
−
= = =
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Chapter 14, Problem 77. A series RLC circuit has R = 10Ω , ω 0 = 40 rad/s, and B = 5 rad/s. Find L and C when the circuit is scaled: (a) in magnitude by a factor of 600, (b) in frequency by a factor of 1,000,
(c) in magnitude by a factor of 400 and in frequency by a factor of 10 5 . Chapter 14, Solution 77. L and C are needed before scaling.
H25
10BR
LLR
B ===⎯→⎯=
F5.312)2)(1600(
1L
1C
LC1
20
0 µ==ω
=⎯→⎯=ω
(a) ===′ )2)(600(LKL m H1200
=×
==′ 60010125.3
KC
C-4
mF5208.0 µ
(b) ===′ 3f 10
2KL
L mH2
=×
==′ 3
-4
f 1010125.3
KC
C nF5.312
(c) ===′ 5f
m
10)2)(400(
LKK
L mH8
=×
==′ )10)(400(10125.3
KKC
C 5
-4
fmpF81.7
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 78. Redesign the circuit in Fig. 14.85 so that all resistive elements are scaled by a factor of 1,000 and all frequency-sensitive elements are frequency-scaled by a factor of 10 4 . Chapter 14, Solution 78.
Ω===′ k1)1)(1000(RKR m
H1.0)1(1010
LKK
L 4
3
f
m ===′
F1.0)10)(10(
1KK
CC 43
fmµ===′
The new circuit is shown below.
1 kΩ
+
Vx
−
1 kΩ 0.1 HI 0.1 µF 1 kΩ
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Chapter 14, Problem 79. * Refer to the network in Fig. 14.96. (a) Find Z in (s).
(b) Scale the elements by K m = 10 and K f = 100. Find Z in (s) and ω 0 .
Figure 14.96 For Prob. 14.79. * An asterisk indicates a challenging problem.
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Chapter 14, Solution 79. (a) Insert a 1-V source at the input terminals.
There is a supernode.
sC1sLR1 21
+=
− VV (1)
But o12o21 33 VVVVVV −=⎯→⎯+= (2)
Also, sC1sLsLsC1sL
sL 2o2o +
=⎯→⎯+
=VV
VV (3)
Combining (2) and (3)
oo12 sLsC1sL
3 VVVV+
=−=
12
2
o LCs41LCs
VV+
= (4)
Substituting (3) and (4) into (1) gives
12o1
LCs41sC
sLR1
VVV
+==
−
12
2
121 LCs41sRCLCs41
LCs41sRC
1 VVV+
++=
++=
sRCLCs41LCs41
2
2
1 +++
=V
)sRCLCs41(RsRC
R1
21
o ++=
−=
VI
sCLCs4sRC11 2
oin
++==
IZ
sC1
RsL4in ++=Z (5)
Ro
1/sC R
+ − sL1 V
V1 V2Io
+
Vo
−
3Vo
+ −
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When 5R = , 2L = , 1.0C = ,
=)s(inZs
105s8 ++
At resonance,
C1
L40)Im( in ω−ω==Z
or ===ω)2)(1.0(2
1LC21
0 s/rad118.1
(b) After scaling,
RKR m⎯→⎯′ Ω⎯→⎯Ω 404 Ω⎯→⎯Ω 505
H2.0)2(10010
LKK
Lf
m ===′
4-
fm10
)100)(10(1.0
KKC
C ===′
From (5),
=)s(inZs
1050s8.0
4
++
===ω)10)(2.0(2
1LC21
4-0 s/rad8.111
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Chapter 14, Problem 80. (a) For the circuit in Fig. 14.97, draw the new circuit after it has been scaled by K m = 200 and K f = 10 4 .
(b) Obtain the Thevenin equivalent impedance at terminals a-b of the scaled circuit at ω = 10 4 rad/s.
Figure 14.97 For Prob. 14.80. Chapter 14, Solution 80.
(a) Ω===′ 400)2)(200(RKR m
mH2010
)1)(200(K
LKL 4
f
m ===′
F25.0)10)(200(
5.0KK
CC 4
fmµ===′
The new circuit is shown below.
0.25 µF
Ix
400 Ω
20 mH
0.5 Ix
a
b
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(b) Insert a 1-A source at the terminals a-b.
At node 1,
sL
sC1 211
VVV
−+= (1)
At node 2,
R
5.0sL
2x
21 VI
VV=+
−
But, 1x sC VI = .
RsC5.0
sL2
121 V
VVV
=+−
(2)
Solving (1) and (2),
1sCR5.0LCs
RsL21 ++
+=V
1sCR5.0LCsRsL
1 21
Th +++
==V
Z
At 410=ω ,
1)400)(1025.0)(10j(5.0)1025.0)(1020()10j(400)1020)(10j(
6-46-3-24
3-4
Th +×+××+×
=Z
200j6005.0j5.0
200j400Th −=
++
=Z
=ThZ ohms435.18-5.632 °∠
1 A 1/(sC)
Ix
R
sL
0.5 Ix
a
b
V1 V2
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Chapter 14, Problem 81. The circuit shown in Fig. 14.98 has the impedance
Z(s) = )501)(501(
)1(000,1jsjs
s−+++
+ , s=jω
Find: (a) the values of R, L, C, and G
(b) the element values that will raise the resonant frequency by a factor of 10 3 by frequency scaling
Figure 14.98 For Prob. 14.81.
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Chapter 14, Solution 81. (a)
1GR)LGRC(jLCRLjZtoleadswhich
LjR1)LjR)(CjG(
LjR1CjG
Z1
2 +++ω+ω−
+ω=
ω++ω+ω+
=ω+
+ω+=
LC1GR
CG
LRj
LCR
Cj
)(Z2 +
+⎟⎠⎞
⎜⎝⎛ +ω+ω−
+ω
=ω (1)
We compare this with the given impedance:
25001j2)1j(1000)(Z 2 ++ω+ω−
+ω=ω (2)
Comparing (1) and (2) shows that
LR1 R/LmF, 1C1000C1
=⎯→⎯==⎯→⎯=
1CG2CG
LR
==⎯→⎯=+ mS
L4.0RR10
1R10LC
1GR25013
3==⎯→⎯
+=
+=
−
−
Thus,
R = 0.4Ω, L = 0.4 H, C = 1 mF, G = 1 mS
(b) By frequency-scaling, Kf =1000. R’ = 0.4 Ω, G’ = 1 mS
mH4.010
4.0KL'L 3f
=== , F11010
KC'C 3
3
fµ===
−
−
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 82. Scale the lowpass active filter in Fig. 14.99 so that its corner frequency increases from 1 rad/s to 200 rad/s. Use a 1-µ F capacitor.
Figure 14.99 For Prob. 14.82. Chapter 14, Solution 82.
fmKK
CC =′
2001
200K c
f ==ωω′
=
50002001
101
K1
CC
K 6-f
m =⋅=⋅′
=
==′ RKR m 5 kΩ, thus, ==′ if R2R Ωk10
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Chapter 14, Problem 83. The op amp circuit in Fig. 14.100 is to be magnitude-scaled by 100 and frequency-scaled by 10 5 . Find the resulting element values.
Figure 14.100 For Prob. 14.83. Chapter 14, Solution 83.
pF 1.010x100
10CKK
1'CF1 5
6
fm===⎯→⎯µ
−
pF 5.0'CF5 =⎯→⎯µ
Ω=Ω==⎯→⎯Ω M 1k 10x100RK'Rk 10 m
Ω=⎯→⎯Ω M 2'Rk 20
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Chapter 14, Problem 84.
Using PSpice, obtain the frequency response of the circuit in Fig. 14.101 on the next page.
Figure 14.101 For Prob. 14.84. Chapter 14, Solution 84.
The schematic is shown below. A voltage marker is inserted to measure vo. In the AC sweep box, we select Total Points = 50, Start Frequency = 1, and End Frequency = 1000. After saving and simulation, we obtain the magnitude and phase plots in the probe menu as shown below.
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Chapter 14, Problem 85. Use PSpice to obtain the magnitude and phase plots of V 0 /I s of the circuit in Fig. 14.102.
Figure 14.102 For Prob. 14.85. Chapter 14, Solution 85. We let o
s 01I ∠= A so that .VI/V oso = The schematic is shown below. The circuit is simulated for 100 < f < 10 kHz.
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Chapter 14, Problem 86. Use PSpice to provide the frequency response (magnitude and phase of i) of the circuit in Fig. 14.103. Use linear frequency sweep from 1 to 10,000 Hz.
Figure 14.103 For Prob. 14.86. Chapter 14, Solution 86.
The schematic is shown below. A current marker is inserted to measure I. We set Total Points = 101, start Frequency = 1, and End Frequency = 10 kHz in the AC sweep box. After simulation, the magnitude and phase plots are obtained in the Probe menu as shown below.
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Chapter 14, Problem 87. In the interval 0.1 < f < 100 Hz, plot the response of the network in Fig. 14.104. Classify this filter and obtain ω 0 .
Figure 14.104 For Prob. 14.87.
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Chapter 14, Solution 87.
The schematic is shown below. In the AC Sweep box, we set Total Points = 50, Start Frequency = 1, and End Frequency = 100. After simulation, we obtain the magnitude response as shown below. It is evident from the response that the circuit represents a high-pass filter.
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Chapter 14, Problem 88. Use PSpice to generate the magnitude and phase Bode plots of V 0 in the circuit of Fig. 14.105.
Figure 14.105 For Prob. 14.88. Chapter 14, Solution 88.
The schematic is shown below. We insert a voltage marker to measure Vo. In the AC Sweep box, we set Total Points = 101, Start Frequency = 1, and End Frequency = 100. After simulation, we obtain the magnitude and phase plots of Vo as shown below.
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Chapter 14, Problem 89. Obtain the magnitude plot of the response V 0 in the network of Fig. 14.106 for the frequency interval 100 < f < 1,000 Hz..
Figure 14.106 For Prob. 14.89.
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Chapter 14, Solution 89.
The schematic is shown below. In the AC Sweep box, we type Total Points = 101, Start Frequency = 100, and End Frequency = 1 k. After simulation, the magnitude plot of the response Vo is obtained as shown below.
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Chapter 14, Problem 90. Obtain the frequency response of the circuit in Fig. 14.40 (see Practice Problem 14.10). Take R 1 = R 2 = 100Ω , L =2 mH. Use 1 < f < 100,000 Hz. Chapter 14, Solution 90.
The schematic is shown below. In the AC Sweep box, we set Total Points = 1001, Start Frequency = 1, and End Frequency = 100k. After simulation, we obtain the magnitude plot of the response as shown below. The response shows that the circuit is a high-pass filter.
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Chapter 14, Problem 91. For the “tank” circuit of Fig. 14.79, obtain the frequency response (voltage across the capacitor) using PSpice. Determine the resonant frequency of the circuit. Chapter 14, Solution 91. The schematic is shown below. In the AC Sweep box, we select Total Points = 101, Start Frequency = 10, and End Frequency = 10 k. After simulation, the magnitude plot of the frequency response is obtained. From the plot, we obtain the resonant frequency fo is approximately equal to 800 Hz so that ωo = 2πfo = 5026 rad/s.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Problem 92. Using PSpice, plot the magnitude of the frequency response of the circuit in Fig. 14.85. Chapter 14, Solution 92.
The schematic is shown below. We type Total Points = 101, Start Frequency = 1, and End Frequency = 100 in the AC Sweep box. After simulating the circuit, the magnitude plot of the frequency response is shown below.
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Chapter 14, Problem 93. For the phase shifter circuit shown in Fig. 14.107, find H = V o /V s .
Figure 14.107 For Prob. 14.93. Chapter 14, Solution 93. Consider the circuit as shown below.
1
1
1 1sVsCV VsRCR
sC
= =++
2 1s sR sRCV V V
R sC sRC= =
+ +
1 211o s
sRCV V V VsRC
−= − =
+
Hence,
1( )1
o
s
V sRCH sV sRC
−= =
+
+ _ Vs
C
R C
R
+ _ Vo V1 V2
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Chapter 14, Problem 94.
For an emergency situation, an engineer needs to make an RC highpass filter. He has one 10-pF capacitor, one 30-pF capacitor, one 1.8-kΩ resistor, and one 3.3-kΩ resistor available. Find the greatest cutoff frequency possible using these elements. Chapter 14, Solution 94.
RC1
c =ω
We make R and C as small as possible. To achieve this, we connect 1.8 kΩ and 3.3 kΩ in parallel so that
Ω=+
= k 164.13.38.13.3x8.1R
We place the 10-pF and 30-pF capacitors in series so that
C = (10x30)/40 = 7.5 pF Hence,
rad/s 10x55.11410x5.7x10x164.1
1RC1 6
123c ===ω−
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Chapter 14, Problem 95.
A series-tuned antenna circuit consists of a variable capacitor (40 pF to 360 pF) and a 240-µ H antenna coil that has a dc resistance of 12Ω .
(a) Find the frequency range of radio signals to which the radio is tunable. (b) Determine the value of Q at each end of the frequency range. Chapter 14, Solution 95.
(a) LC2
1f0 π=
When pF360C = ,
MHz541.0)10360)(10240(2
1f
12-6-0 =××π
=
When pF40C = ,
MHz624.1)1040)(10240(2
1f
12-6-0 =××π
=
Therefore, the frequency range is MHz624.1fMHz541.0 0 <<
(b) RfL2
Qπ
=
At MHz541.0f0 = ,
=××π
=12
)10240)(10541.0)(2(Q
-66
98.67
At MHz624.1f0 = ,
=××π
=12
)10240)(10624.1)(2(Q
-66
1.204
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Chapter 14, Problem 96.
The crossover circuit in Fig. 14.108 is a lowpass filter that is connected to a woofer. Find the transfer function H(ω ) = V o (ω )/V i (ω )
Figure 14.108 For Prob. 14.96. Chapter 14, Solution 96.
L
RL
Ri
+ −
Vi
V1 Vo
+
Vo
−
C1 C2
Z2 Z1
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22
L
2L1 CsR1
RsC
1||R
+==Z
⎟⎠
⎞⎜⎝
⎛
+++
=+=2L
2L2
L
11
12 CsR1
LCRsRsL||
sC1
)sL(||sC1
ZZ
2L
2L2
L
1
2L
2L2
L
12
CsR1LCRsRsL
sC1
CsR1LCRsRsL
sC1
+++
+
+++
⋅=Z
21L3
1L12
2L
2L2
L2 CLCRsCsRLCsCsR1
LCRsRsL++++
++=Z
ii2
21 R
VZ
ZV
+=
i1
1
22
21
1
1o sLRsL
VZ
ZZ
ZV
ZZ
V+
⋅+
=+
=
sLR 1
1
22
2
i
o
+⋅
+=
ZZ
ZZ
VV
where
=+ 22
2
RZZ
21Li3
1Li1i2
2Lii2L2
L
2L2
L
CLCRRsCRsRLCRsCRsRRLCRsRsLLCRsRsL
+++++++++
and 2L
2L
L
1
1
LCRssLRR
sL ++=
+ZZ
Therefore,
=i
o
VV
)LCRssLR)(CLCRRsCRsRLCRsCRsRRLCRsRsL(
)LCRsRsL(R
2L2
L21Li3
1Li1i2
2Lii2L2
L
2L2
LL
+++
++++++++
where ω= js .
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Chapter 14, Problem 97. The crossover circuit in Fig. 14.109 is a highpass filter that is connected to a tweeter. Determine the transfer function H(ω ) = V o (ω )/V i (ω ).
Figure 14.109 For Prob. 14.97.
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Chapter 14, Solution 97.
2L
2L
2L sC1sLR
)sC1R(sLsC
1R||sL
+++
=⎟⎠
⎞⎜⎝
⎛+=Z , ω= js
i1i
1 sC1RV
ZZ
V++
=
i1i2L
L1
2L
Lo sC1RsC1R
RsC1R
RV
ZZ
VV++
⋅+
=+
=
)sC1sLR)(sC1R()sC1R(sL)sC1R(sL
sC1RR
)(2L1i2L
2L
2L
L
i
o
++++++
⋅+
==ωVV
H
=ω)(H)1CsR(LCs)1CsRLCs)(1CsR(
CCLRs
2L12
2L22
1i
21L3
+++++
where ω= js .
L
RL
Ri
+ −
Vi
V1 Vo
+
Vo
−
C1 C2
Z2 Z1
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Chapter 14, Problem 98. A certain electronic test circuit produced a resonant curve with half-power points at 432 Hz and 454 Hz. If Q = 20, what is the resonant frequency of the circuit? Chapter 14, Solution 98.
π=−π=−π=ω−ω= 44)432454(2)ff(2B 1212
)44)(20(QBf2 00 π==π=ω
==ππ
= )22)(20(2
)44)(20(f0 Hz440
Chapter 14, Problem 99. In an electronic device, a series circuit is employed that has a resistance of 100Ω , a capacitive reactance of 5 kΩ , and an inductive reactance of 300Ω when used at 2 MHz. Find the resonant frequency and bandwidth of the circuit. Chapter 14, Solution 99.
Cf21
C1
Xc π=
ω=
π=
××π=
π=
2010
)105)(102)(2(1
Xf21
C-9
36c
Lf2LX L π=ω=
π×
=×π
=π
=4103
)102)(2(300
f2X
L-4
6L
=
π⋅
π×
π
=π
=
2010
4103
2
1LC2
1f
9-4-0 MHz165.8
=⎟⎠⎞
⎜⎝⎛
×π
== 4-1034
)100(LR
B s/rad10188.4 6×
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Chapter 14, Problem 100. In a certain application, a simple RC lowpass filter is designed to reduce high frequency noise. If the desired corner frequency is 20 kHz and C = 0.5µ F find the value of R. Chapter 14, Solution 100.
RC1
f2 cc =π=ω
=××π
=π
=)105.0)(1020)(2(
1Cf2
1R 6-3
cΩ91.15
Chapter 14, Problem 101. In an amplifier circuit, a simple RC highpass filter is needed to block the dc component while passing the time-varying component. If the desired rolloff frequency is 15 Hz and C = 10µ F find the value of R. Chapter 14, Solution 101.
RC1
f2 cc =π=ω
=×π
=π
=)1010)(15)(2(
1Cf2
1R 6-
cΩk061.1
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Chapter 14, Problem 102. Practical RC filter design should allow for source and load resistances as shown in Fig. 14.110. Let R = 4kΩ and C = 40-nF. Obtain the cutoff frequency when: (a) R s = 0, R L = ∞ ,
(b) R s = 1kΩ , R L = 5kΩ .
Figure 14.110 For Prob. 14.102. Chapter 14, Solution 102.
(a) When 0R s = and ∞=LR , we have a low-pass filter.
RC1
f2 cc =π=ω
=××π
=π
=)1040)(104)(2(
1RC21
f 9-3c Hz7.994
(b) We obtain ThR across the capacitor.
)RR(||RR sLTh += Ω=+= k5.2)14(||5R Th
)1040)(105.2)(2(1
CR21
f 9-3Th
c ××π=
π=
=cf kHz59.1
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Chapter 14, Problem 103. The RC circuit in Fig. 14.111 is used for a lead compensator in a system design. Obtain the transfer function of the circuit.
Figure 14.111 For Prob. 14.103. Chapter 14, Solution 103.
Cj1||RRR)(12
2
i
oω+
==ωVV
H , ω= js
)sC1)(RR(RR)sC1R(R
sC1R)sC1(RR
R)s(2121
12
1
12
2+++
=
++
=H
=)s(H2121
12RsCRRR)sCR1(R
+++
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Chapter 14, Problem 104. A low-quality-factor, double-tuned bandpass filter is shown in Fig. 14.112. Use PSpice to generate the magnitude plot of V o (ω ).
Figure 14.112 For Prob. 14.104.
PROPRIETARY MATERIAL. © 2007 The McGraw-Hill Companies, Inc. All rights reserved. No part of this Manual may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGraw-Hill for their individual course preparation. If you are a student using this Manual, you are using it without permission.
Chapter 14, Solution 104. The schematic is shown below. We click Analysis/Setup/AC Sweep and enter Total Points = 1001, Start Frequency = 100, and End Frequency = 100 k. After simulation, we obtain the magnitude plot of the response as shown.
