高频电子线路第2章习题测验答案
第2章 小信号选频放大器
2.1 已知并联谐振回路的1μH,20pF,100,L C Q ===求该并联回路的谐振频率0f 、谐振电阻p R 及通频带0.7BW 。 [解] 90-6120.035610Hz 35.6MHz 2π2π102010f LC
H F
-=
=
=?=??
6312
640.71010022.4k 22.361022.36k 201035.610Hz
35.610Hz 356kH z
100
p H
R Q F
f BW Q ρρ--===Ω=?Ω=Ω??===?=
2.2 并联谐振回路如图P2.2所示,已知:300pF,390μH,100,C L Q ===信号源内阻s 100k ,R =Ω负载电阻L 200k ,R =Ω求该回路的谐振频率、谐振电阻、通频带。 [解] 0465kHz 2π2π390μH 300PF
f LC
≈
=
=?
0.70390μH
100
114k Ω
300PF
////100k Ω//114.k Ω//200k Ω=42k Ω42k Ω
37
1.14k Ω
390μH/300 PF
/465kHz/37=12.6kHz
p e s p L
e
e e R Q R R R R R Q BW
f Q ρρ
======
=
=
===
2.3 已知并联谐振回路的00.710MHz,C=50pF,150kHz,f BW ==求回路的L 和Q 以及
600kHz f ?=时电压衰减倍数。如将通频带加宽为300 kHz ,应在回路两端并接一个多大的电阻?
[解] 626212
011
5105μH (2π)(2π1010)5010
L H f C --===?=???? 6
03
0.7101066.715010f Q BW ?===?
22
36
022*********.78.11010p o
U f Q f U ?
?
???????=+=+= ? ?????
?
当0.7300kHz BW =时
6
03
0.74612
010
1033.3
3001033.3
1.061010.6k 2π2π10105010
e e e e
f Q BW Q R Q f C ρ-?===?====?Ω=Ω????
而
4712
66.7
2.131021.2k 2π105010
p R Q ρ-==
=?Ω=Ω??? 由于,p e p
RR R R R =
+所以可得
10.6k 21.2k 21.2k 21.2k 10.6k e p p e
R R R R R Ω?Ω
=
=
=Ω-Ω-Ω
2.4 并联回路如图P2.4所示,已知:360pF,
C =1280μH,L ==100,Q 250μH,L =
12=/10,n N N =L 1k R =Ω。试求该并联回路考虑到L R 影响后的通频带及等效谐振电阻。
[解] 6
312
28010100881088k 36010
p R Q ρ--?===?Ω=Ω? 226
3
3312
00.7612101k 100k //88k //100k 46.8k 2801046.81046.810/0.881053360109.46kHz
2π532π2801036010
L
L e p L
e
e e e R n R R R R R Q
f BW Q Q LC ρ----'==?Ω=Ω'==ΩΩ=Ω?==???=?====???? 2.5 并联回路如图P2.5所示,试求并联回路2-3两端的谐振电阻p R '。
已知:(a)1100μH L =、210μH L =、4μH M =,等效损耗电阻10r =Ω,300pF C =;(b) 150pF C =、2100pF C =,10μH L =、2r =Ω。
[解]
6
12
12
2(1001042)10
(a)39.3k
30010
10
p
L L M
L
R
cr
Cr
-
-
++++??
====Ω
??
6
12
6
2
22
2(100108)10
8.43
(104)10
39.3k
0.55k
(8.43)
p
p
L L M
n
L M
R
R
n
-
-
++++?
===
++?
Ω
'===Ω
12
12
12
12
12
6
6
12
12
12
12
1
22
(50100)10
(b)33.310pF=33.3pF
(50100)10
1010
0.15010150k
33.3102
(50100)10
3
5010
150k
16.7k
3
p
p
p
C C
C
C C
L
R
Cr
C C
n
C
R
R
n
-
-
-
-
-
-
-
??
===?
++?
?
===?Ω=Ω
??
++?
===
?
Ω
'===Ω
2.6并联谐振回路如图P2.6所示。已知:
10MHz
f=,100
Q=,12k
s
R=Ω,
L
1k
R=Ω,40pF
C=,
匝比
11323
/ 1.3
n N N
==,
21345
/4
n N N
==,试求谐振回路有载谐振电阻
e
R、有载品质因数
e
Q和回路
通频带
0.7
BW。
[解]将图P2.6等效为图P2.6(s),图中
712
100
39.8k
2π2π104010
p
Q
R Q
f C
ρ
-
====Ω
???
2212
223
371201.312k 20.28k 41k 16k ////(20.28//39.8//16)k 7.3k 7.3107.3102π10401018.34
1/2πs s L L e s p L
e
e R n R R n R R R R R R Q
f C
ρ-'==?Ω=Ω
'==?Ω=Ω
''==Ω=Ω?===?????=
0.7010MHz
/0.545MHz 18.34
e BW
f Q ==
=
2.7 单调谐放大器如图2.2.4(a)所示。已知放大器的中心频率010.7MHz f =,回路线圈电感134μH L =,
100Q =,匝数1320N =匝,125N =匝,455N =匝,2mS L G =,晶体管的参数为:200μS oe G =、7pF oe C =、m 45mS g =、0bb r '≈。试求该大器的
谐振电压增益、通频带及回路外接电容C。 [解] 131312124520
20
4,45
5
N N n n N N =
===
== 666
01326261232626631211137.2102π1002π10.710410
/20010/412.510/210/412510(37.212.5125)10174.710451044174.710p oe
oe L L e p oe
L m uo e G S Q Q f L G G n S G G n S
G G G G S g A n n G ρ----------=
===???????'==?=?'==?=?''=++=++?=?--?==???6666
0.70122626
022
116
11
21
174.7102π10.710410/10.7/210.51MHz 11
55.41055.4(2π)(2π10.710)410
7
55.4554e e e T oe T Q G BW f Q C F PF f L C C C PF n ρ
----=-=
=
=??????====
==?=????=-
=-=
2.8 单调谐放大器如图2.2.4(a)所示。中心频率030MHz f =,晶体管工作点电流EQ 2mA I =,回路电
感13 1.4μH L =,100Q =,匝比11312/2n N N ==,21345/ 3.5n N N ==,L 1.2mS G =、0.4mS oe G =,0bb r '≈,试求该放大器的谐振电压增益及通频带。
[解] 666
11
38101002π3010 1.410
p G S Q ρ--=
==??????
23261232626606
126013/0.410/210010/ 1.210/3.59810(3810098)1023610/262mA /26mV 0.0770.077
46.62 3.52361011
236102π3oe
oe L L e p oe
L m EQ m u e e e G G n S G G n S
G G G G S g I S g A n n G Q G w L ------?
--'==?=?'==?=?''=++=++?=?===--===-???==???66
600.7
16010 1.410
3010 1.88MHz 16
e f BW Q -=????===