模擬電子技術基礎課件-9

負反饋放大電路的分析計算常用方法a.等效電路法5.3負反饋放大電路的分析及近似計算等效電路法分離法近似計算法把放大器中的非線性器件用線性電路等效，然后根據(jù)電路理論求解各項指標。負反饋放大電路的分析計算常用方法a.等效電路法5.3(b)分別求出基本放大電路的A、Ri、Ro、fH和fL等指標及反饋網(wǎng)絡的反饋系數(shù)F。(c)分別求出Af、Rid、Rof、fHf和fLf等指標。(a)分負反饋放大電路為基本放大電路和反饋網(wǎng)絡兩部分。分離法的基本思想b.分離法(b)分別求出基本放大電路的A、Ri、Ro、fH和f由于集成運算放大器和多級放大電路的放大倍數(shù)一般都比較大，很容易使放大電路滿足深度負反饋的條件。放大電路滿足深度負反饋的條件5.3.1深度負反饋放大電路近似計算的一般方法1.采用近似計算的條件由于集成運算放大器和多級放大電路的放大倍數(shù)一般都比較大，很容在深度負反饋（AF>>1）的條件下··XoXi·XoXf≈·F·≈1Af=A1+AF·······F=XfXo代入上式得將XoXi··Af=·3.近似計算的原理在深度負反饋（AF>>1）的條件下··XoXi·XoXf≈·Xid≈0··XoXi·XoXf≈·由得(1)當電路引入串聯(lián)負反饋時·Uf·Ui≈·Uid≈0(稱為虛短)·Xf·Xi≈·Xid≈0··XoXi·XoXf≈·由得(1)當電(2)當電路引入并聯(lián)負反饋時·If·Ii≈·Iid≈0(稱為虛斷）由于基本放大電路的電壓放大倍數(shù)也很大，條件·Uid≈0也同時成立。(2)當電路引入并聯(lián)負反饋時·If·Ii≈·Iid≈0(1．電壓串聯(lián)負反饋（同相輸入比例放大器）5.3.2電壓模運放組成的反饋電路+A+Uid+F++UfUiUoRLR2R1????_____1．電壓串聯(lián)負反饋（同相輸入比例放大器）5.3.2電壓根據(jù)電路在深度負反饋條件下的分析依據(jù)有Uid≈0(虛短)·U+≈U–··+A+Uid+F++UfUiUoRLR2R1????_____根據(jù)電路在深度負反饋條件下的分析依據(jù)有Uid≈0由于U+≈Ui·····+A+Uid+F++UfUiUoRLR2R1????_____由于U+≈Ui·····+A+Uid+F++UfUiUoR故電路的閉環(huán)電壓放大倍數(shù)·····+A+Uid+F++UfUiUoRLR2R1????_____故電路的閉環(huán)電壓放大倍數(shù)·····+A+Uid+F++URif≈∞閉環(huán)輸入電阻

Rof≈0閉環(huán)輸出電阻RifRof+A+Uid+F++UfUiUoRLR2R1????_____Rif≈∞閉環(huán)輸入電阻Rof≈0閉環(huán)輸出電阻RifRo2．電壓并聯(lián)負反饋（反相輸入比例放大器）

在深度負反饋條件下RL?+A+UoUsF+R1R2IiIidIf????___2．電壓并聯(lián)負反饋（反相輸入比例放大器）在深度負反饋條件下由Iid≈0(虛斷)知·Ii≈If??RL?+A+UoUsF+R1R2IiIidIf????___由Iid≈0(虛斷)知·Ii≈If??RL?+A+Uo由Uid≈0(虛短)知···RL?+A+UoUsF+R1R2IiIidIf????___由Uid≈0(虛短)知···RL?+A+UoUsF+R1R········而RL?+A+UoUsF+R1R2IiIidIf????___········而RL?+A+UoUsF+R1R2IiIid故閉環(huán)互阻增益···RL?+A+UoUsF+R1R2IiIidIf????___故閉環(huán)互阻增益···RL?+A+UoUsF+R1R2IiI閉環(huán)電壓放大倍數(shù)···RL?+A+UoUsF+R1R2IiIidIf????___閉環(huán)電壓放大倍數(shù)···RL?+A+UoUsF+R1R2IiI輸入電阻RifRL?+A+UoUsF+R1R2IiIidIf????___輸入電阻RifRL?+A+UoUsF+R1R2IiIidIf輸出電阻RofRL?+A+UoUsF+R1R2IiIidIf????___輸出電阻RofRL?+A+UoUsF+R1R2IiIidIf3．電流串聯(lián)負反饋——電壓電流變換器由于····+A+Uid+++UfUiUoRLR????Io?F_____3．電流串聯(lián)負反饋——電壓電流變換器由于····+A+U故電路的閉環(huán)互導增益·······+A+Uid+++UfUiUoRLR????Io?F_____故電路的閉環(huán)互導增益·······+A+Uid+++UfUi閉環(huán)電壓放大倍數(shù)······+A+Uid+++UfUiUoRLR????Io?F_____閉環(huán)電壓放大倍數(shù)······+A+Uid+++UfUiUoR輸入、輸出電阻RifRof+A+Uid+++UfUiUoRLR????Io?F_____輸入、輸出電阻RifRof+A+Uid+++UfUiUoRL4．電流并聯(lián)負反饋——電流放大器在深度負反饋的條件下Ii≈If··Ui≈0·+A+UoUi+F+R1R2R3???????____RL4．電流并聯(lián)負反饋——電流放大器在深度負反饋的條件下Ii輸入電流··反饋電流··+A+UoUi+F+R1R2R3???????____RL輸入電流··反饋電流··+A+UoUi+F+R1R2R3??閉環(huán)電流放大倍數(shù)·······+A+UoUi+F+R1R2R3???????____RL閉環(huán)電流放大倍數(shù)·······+A+UoUi+F+R1R2R閉環(huán)電壓放大倍數(shù)······+A+UoUi+F+R1R2R3???????____RL閉環(huán)電壓放大倍數(shù)······+A+UoUi+F+R1R2R3輸入、輸出電阻RifRof+A+UoUi+F+R1R2R3???????____RL輸入、輸出電阻RifRof+A+UoUi+F+R1R2R3?1．電壓串聯(lián)負反饋5.3.3分立元件組成的反饋電路F++–+VCCT1++T2+++–+––+1．電壓串聯(lián)負反饋5.3.3分立元件組成的反饋電路F+⊕⊕⊕(1)負反饋的判斷F++–+VCCT1++T2+++–+––+⊕⊕⊕(1)負反饋的判斷F++–+VCCT1++T2+++(2)閉環(huán)電壓放大倍數(shù)··由于F++–+VCCT1++T2+++–+––+(2)閉環(huán)電壓放大倍數(shù)··由于F++–+VCCT1++T·····F++–+VCCT1++T2+++–+––+·····F++–+VCCT1++T2+++–+––+(3)輸入電阻RifF++–+VCCT1++T2+++–+––+(3)輸入電阻RifF++–+VCCT1++T2+++–(4)輸出電阻RofF++–+VCCT1++T2+++–+––+(4)輸出電阻RofF++–+VCCT1++T2+++–2．電流并聯(lián)負反饋++VCCT1+T2+F–+++––2．電流并聯(lián)負反饋++VCCT1+T2+F–+++––⊕(1)負反饋的判斷++VCCT1+T2+F–+++––⊕(1)負反饋的判斷++VCCT1+T2+F–+++––由于反饋電流iF來自于輸出級晶體管T2集電極電流iC2故電路穩(wěn)定的是iC2，而不是負載電流iOiC2iE2iO++VCCT1+T2+F–+++––由于反饋電流iF來自于輸出級晶體管T2集電極電流iC2故(2)閉環(huán)電流放大倍數(shù)·····FiC2iE2iO++VCCT1+T2+–+++––(2)閉環(huán)電流放大倍數(shù)·····FiC2iE2iO++V(3)閉環(huán)電壓放大倍數(shù)······iC2iE2iO++VCCT1+T2+F–+++––(3)閉環(huán)電壓放大倍數(shù)······iC2iE2iO++V(4)輸入電阻RifR'ifiC2iE2iO++VCCT1+T2+F–+++––(4)輸入電阻RifR'ifiC2iE2iO++VCC(5)輸出電阻從T2集電極看進去的閉環(huán)輸出電阻從負載看進去的輸出電阻RofR'ofiC2iE2iO++VCCT1+T2+F–+++––(5)輸出電阻從T2集電極看進去的閉環(huán)輸出電阻從負載看5.3.4電流模運放的閉環(huán)特性電流模運放同相輸入放大電路Ui?+1RiIi?RZCZ+1Ii?Uo?R1R2I2?Uf?+–5.3.4電流模運放的閉環(huán)特性電流模運放同相輸入放大低頻閉環(huán)電壓放大倍數(shù)在深度負反饋的條件下Ui?+1RiIi?RZCZ+1Ii?Uo?R1R2I2?Uf?+–低頻閉環(huán)電壓放大倍數(shù)在深度負反饋的條件下Ui?+1RiIi?分析電路的高頻特性Ui?+1RiIi?RZCZ+1Ii?Uo?R1R2I2?Uf?+–分析電路的高頻特性Ui?+1RiIi?RZCZ+1Ii?Uo由圖可知·······Ui?+1RiIi?RZCZ+1Ii?Uo?R1R2I2?Uf?+–由圖可知·······Ui?+1RiIi?RZCZ+1Ii?······Ui?+1RiIi?RZCZ+1Ii?Uo?R1R2I2?Uf?+–······Ui?+1RiIi?RZCZ+1Ii?Uo?R1由以上各式得電路的高頻閉環(huán)特性···由于···當Auf0Ri<<R2時·由以上各式得電路的高頻閉環(huán)特性···由于···當Auf0R·由式得電路的閉環(huán)上限截止頻率為結(jié)論(1)fHf僅與CZ、R2有關，而與R1無關。(2)電流模運放的閉環(huán)電壓放大倍數(shù)增大時，帶寬增益積有所增加?！び墒降秒娐返拈]環(huán)上限截止頻率為結(jié)論(1)fHf僅與C電流模運放幅頻特性.dB/||lg20fuAlg20R1R2R1+OfHfflg20R2+電流模運放幅頻特性.dB/||lg20fuAlg20R1R2電壓模運放幅頻特性電壓模運放帶寬增益積等于常數(shù).dB/||lg20fuAlg20R1R2R1+0fHfflg20R2+電壓模運放幅頻特性電壓模運放帶寬增益積等于常數(shù).dB/||l負反饋放大電路的分析計算常用方法a.等效電路法5.3負反饋放大電路的分析及近似計算等效電路法分離法近似計算法把放大器中的非線性器件用線性電路等效，然后根據(jù)電路理論求解各項指標。負反饋放大電路的分析計算常用方法a.等效電路法5.3(b)分別求出基本放大電路的A、Ri、Ro、fH和fL等指標及反饋網(wǎng)絡的反饋系數(shù)F。(c)分別求出Af、Rid、Rof、fHf和fLf等指標。(a)分負反饋放大電路為基本放大電路和反饋網(wǎng)絡兩部分。分離法的基本思想b.分離法(b)分別求出基本放大電路的A、Ri、Ro、fH和f由于集成運算放大器和多級放大電路的放大倍數(shù)一般都比較大，很容易使放大電路滿足深度負反饋的條件。放大電路滿足深度負反饋的條件5.3.1深度負反饋放大電路近似計算的一般方法1.采用近似計算的條件由于集成運算放大器和多級放大電路的放大倍數(shù)一般都比較大，很容在深度負反饋（AF>>1）的條件下··XoXi·XoXf≈·F·≈1Af=A1+AF·······F=XfXo代入上式得將XoXi··Af=·3.近似計算的原理在深度負反饋（AF>>1）的條件下··XoXi·XoXf≈·Xid≈0··XoXi·XoXf≈·由得(1)當電路引入串聯(lián)負反饋時·Uf·Ui≈·Uid≈0(稱為虛短)·Xf·Xi≈·Xid≈0··XoXi·XoXf≈·由得(1)當電(2)當電路引入并聯(lián)負反饋時·If·Ii≈·Iid≈0(稱為虛斷）由于基本放大電路的電壓放大倍數(shù)也很大，條件·Uid≈0也同時成立。(2)當電路引入并聯(lián)負反饋時·If·Ii≈·Iid≈0(1．電壓串聯(lián)負反饋（同相輸入比例放大器）5.3.2電壓模運放組成的反饋電路+A+Uid+F++UfUiUoRLR2R1????_____1．電壓串聯(lián)負反饋（同相輸入比例放大器）5.3.2電壓根據(jù)電路在深度負反饋條件下的分析依據(jù)有Uid≈0(虛短)·U+≈U–··+A+Uid+F++UfUiUoRLR2R1????_____根據(jù)電路在深度負反饋條件下的分析依據(jù)有Uid≈0由于U+≈Ui·····+A+Uid+F++UfUiUoRLR2R1????_____由于U+≈Ui·····+A+Uid+F++UfUiUoR故電路的閉環(huán)電壓放大倍數(shù)·····+A+Uid+F++UfUiUoRLR2R1????_____故電路的閉環(huán)電壓放大倍數(shù)·····+A+Uid+F++URif≈∞閉環(huán)輸入電阻

Rof≈0閉環(huán)輸出電阻RifRof+A+Uid+F++UfUiUoRLR2R1????_____Rif≈∞閉環(huán)輸入電阻Rof≈0閉環(huán)輸出電阻RifRo2．電壓并聯(lián)負反饋（反相輸入比例放大器）

在深度負反饋條件下RL?+A+UoUsF+R1R2IiIidIf????___2．電壓并聯(lián)負反饋（反相輸入比例放大器）在深度負反饋條件下由Iid≈0(虛斷)知·Ii≈If??RL?+A+UoUsF+R1R2IiIidIf????___由Iid≈0(虛斷)知·Ii≈If??RL?+A+Uo由Uid≈0(虛短)知···RL?+A+UoUsF+R1R2IiIidIf????___由Uid≈0(虛短)知···RL?+A+UoUsF+R1R········而RL?+A+UoUsF+R1R2IiIidIf????___········而RL?+A+UoUsF+R1R2IiIid故閉環(huán)互阻增益···RL?+A+UoUsF+R1R2IiIidIf????___故閉環(huán)互阻增益···RL?+A+UoUsF+R1R2IiI閉環(huán)電壓放大倍數(shù)···RL?+A+UoUsF+R1R2IiIidIf????___閉環(huán)電壓放大倍數(shù)···RL?+A+UoUsF+R1R2IiI輸入電阻RifRL?+A+UoUsF+R1R2IiIidIf????___輸入電阻RifRL?+A+UoUsF+R1R2IiIidIf輸出電阻RofRL?+A+UoUsF+R1R2IiIidIf????___輸出電阻RofRL?+A+UoUsF+R1R2IiIidIf3．電流串聯(lián)負反饋——電壓電流變換器由于····+A+Uid+++UfUiUoRLR????Io?F_____3．電流串聯(lián)負反饋——電壓電流變換器由于····+A+U故電路的閉環(huán)互導增益·······+A+Uid+++UfUiUoRLR????Io?F_____故電路的閉環(huán)互導增益·······+A+Uid+++UfUi閉環(huán)電壓放大倍數(shù)······+A+Uid+++UfUiUoRLR????Io?F_____閉環(huán)電壓放大倍數(shù)······+A+Uid+++UfUiUoR輸入、輸出電阻RifRof+A+Uid+++UfUiUoRLR????Io?F_____輸入、輸出電阻RifRof+A+Uid+++UfUiUoRL4．電流并聯(lián)負反饋——電流放大器在深度負反饋的條件下Ii≈If··Ui≈0·+A+UoUi+F+R1R2R3???????____RL4．電流并聯(lián)負反饋——電流放大器在深度負反饋的條件下Ii輸入電流··反饋電流··+A+UoUi+F+R1R2R3???????____RL輸入電流··反饋電流··+A+UoUi+F+R1R2R3??閉環(huán)電流放大倍數(shù)·······+A+UoUi+F+R1R2R3???????____RL閉環(huán)電流放大倍數(shù)·······+A+UoUi+F+R1R2R閉環(huán)電壓放大倍數(shù)······+A+UoUi+F+R1R2R3???????____RL閉環(huán)電壓放大倍數(shù)······+A+UoUi+F+R1R2R3輸入、輸出電阻RifRof+A+UoUi+F+R1R2R3???????____RL輸入、輸出電阻RifRof+A+UoUi+F+R1R2R3?1．電壓串聯(lián)負反饋5.3.3分立元件組成的反饋電路F++–+VCCT1++T2+++–+––+1．電壓串聯(lián)負反饋5.3.3分立元件組成的反饋電路F+⊕⊕⊕(1)負反饋的判斷F++–+VCCT1++T2+++–+––+⊕⊕⊕(1)負反饋的判斷F++–+VCCT1++T2+++(2)閉環(huán)電壓放大倍數(shù)··由于F++–+VCCT1++T2+++–+––+(2)閉環(huán)電壓放大倍數(shù)··由于F++–+VCCT1++T·····F++–+VCCT1++T2+++–+––+·····F++–+VCCT1++T2+++–+––+(3)輸入電阻RifF++–+VCCT1++T2+++–+––+(3)輸入電阻RifF++–+VCCT1++T2+++–(4)輸出電阻RofF++–+VCCT1++T2+++–+––+(4)輸出電阻RofF++–+VCCT1++T2+++–2．電流并聯(lián)負反饋++VCCT1+T2+F–+++––2．電流并聯(lián)負反饋++VCCT1+T2+F–+++––⊕(1)負反饋的判斷++VCCT1+T2+F–+++––⊕(1)負反饋的判斷++VCCT1+T2+F–+++––由于反饋電流iF來自于輸出級晶體管T2集電極電流iC2故電路穩(wěn)定的是iC2，而不是負載電流iOiC2iE2iO++VCCT1+T2+F–+++––由于反饋電流iF來自于輸出級晶體管T2集電極電流iC2故(2)閉環(huán)電流放大倍數(shù)·····FiC2iE2iO++VCCT1+T2+–+++––(2)閉環(huán)電流放大倍數(shù)·····FiC2iE2iO++V(3)閉環(huán)電壓放大倍數(shù)······iC2iE2iO++VCCT1+T2+F–+++––(3)閉環(huán)電壓放大倍數(shù)······iC2iE2iO++V(4)輸入電阻RifR'ifiC2iE2iO++VCCT1+T2+F–+++––(4)輸入電阻RifR'ifiC2iE2iO++VCC(5)