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1、放大器的增益BoylestadandNashelskyElectronicDevicesandCircuitTheoryCopyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.2§9-8米勒效應電容(回授電容)輸出電容KCLCMoRo很大∣AV∣>>1↓反相放大器AV<0→(1-)>1→CMo>Cf(決定高頻截止頻率需考慮)3Copyright©2006byPearsonEduca
2、tion,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應（高頻）－3dB點決定因素：網路電容（含寄生電容、經設計所決定C）隨頻率改變的hfe（β）（截止點）【網路參數】【RC組合用以定義高截止頻率】4Copyright©2006byPearsonEducation,Inc. UpperSaddleRi
3、ver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應•求高頻響應曲線轉折點及電壓增益：電壓增益Av（同低頻）（Xc=R）5Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyEl
4、ectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應•頻率響應圖：二倍十倍6dB/二倍20dB/十倍對稱標度二倍6Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應【會影響高頻響應的電容】BJT寄生電
5、容：Cbe，Cbc，Cce接線電容：Cwi，CweRiftftft（max）（min）7Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應接線C過渡C密勒等效C接線C過渡C密勒等效C【高頻交流等效電路】ZiZo8Copyright©2006
6、byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應高高9Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashel
7、skyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應【輸入網路】【輸出網路】【輸出入戴維寧等效電路】10Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應※決定高截止頻率的主要因素：某C所求
8、最低頻率11Copyright©2006byPearsonEducation,Inc. UpperSaddleRiver,NewJersey07458 Allrightsreserved.BoylestadandNashelskyElectronicDevicesandCircuitTheory§9-9BJT放大器的高頻響應【hfe（或β）的變動】hfe：規格表中所列“混和型參數”fβ：由一組“混和π模型參數”來決定rπ（b’）CπCμro擴散電容過渡電容rb’e>>
