模电lecture一滤波电路的基本知识

削弱低频削弱高次或高频干

直流成低通滤波器低通滤波器高通滤波器频段信

抑制干

带通滤波器带通滤波器带阻滤波器

AuAu11fH3有源滤波电 无源滤波电路+电压跟随11Zc(s)11Au(s)Uo(s)

Ui R

1a0a0ss2二阶Au(s) 12 一一阶LPF、HPFa01Au(s)s01s04传递函数分母中s二、低通滤波电(ActiveLow-Pass

Au(s)Uo(s)(1R2 Ui(s)

1AuAup

1jssj1f0UU(s)1AuAu|f RUi1UiU(s)(1R2)UoR15fp设AuAup1R1 01uUo(s)(1 2uUo(s)(1 2)UR13(ss21100U(s)UM(s)AuAup11UM(s)1//(R1R11Ui(s)//(R)61 1AuAup

2|Au2

0.371 PfPAup |Au|ff0

||QAup3

Q3为使fp≈为使fp≈f0,使滤波特性更加理想，需要提高f07压控电压源(VCVS)二阶低通滤波电路(Sallen-KeyLowPass设引入正反馈增大f0 01Aup 01U(s)(1R2)U

A(s) R 1(3 ) R U(s)

1

UM

考虑电路的稳定性，Aup<Ui(s)UM(s)UM(s)UO(s)UM(s)U 8Au

Aup f

0|Au|ff0

Aup

||QAup1j(3Aup

Q 3

3Aup调节Au调节Aup即可调节f0点的增益9三、高通滤波电路(ActiveHigh-PassAuAuAup jff01f R2RAuR

Au |f1 01二阶VCVS高通滤波电二阶VCVS高通滤波电Au

(s 1(3 )0

(s

(f 01 01AuAuf0f0|f1RfQ| |3Aup11(3 )j (f四、带通滤波电路(ActiveBand-Pass要求fpL要求fpL>fpH11j AuAuf

f0 压控电压源二阶带通滤波电

1j(3AufQQ13| o1 R1AupR|Au|ffAuf||QufAu(s)Auf 3Auf01(3 )s(s00f0

AuAuf

jf0

111j(3Auf

f0 f0

f02 f2

jQffp2f0令|求得p1和QQ越大，fbw越窄，对单一频率的选择性越好，且|Aup|五、带阻滤波电路(Band-EliminationFilter,NotchBand-Stop111 RAup|f0,RAup|f0,1 Au(s)up12(2 )s(1f0 Au1f 1(ff0)2j2(2 )Aup AuAup

11(ff01(f)2j2(2Aup)

1j1 BWfBWf00Au|f 0

Q |2(2Aup|

f0|Au 求得fp1和fP22QQ

Cu 等效电流：i

TCT

等效电阻：R

u1TC CfCRR1C1fp

C 1C1C2C2

Aup LPF

1

Aup 101

Aup1j1

1

Aup13s(s

Aup

1j3 (f

0.37 3 LPF

1

RLPFR

1(3Aup

1j(3Aup

3QHPF1sAup 10jfAup 011HPF1RsAup(01(3 )s(sAup fAup(0 1j(3Aup 1f0131RfsAuf 1(3 )s(sAuf fAuf f0 1j(3