【正文】 （ a）（ b）、（ c）是電壓反饋，（ d）是電流反饋；另外（ a）中反饋支路與輸入支路接在晶體管的同一輸入端（基極），故是并聯(lián)反饋，而（ b）（ c）（ d）中反饋支路與輸入支路接在晶體管的不同輸入端，故是串聯(lián)反饋。若 uo=0，則（ a）、（ d）中反饋消失，而（ b）、（ c）中反饋不消失，故（ a）、（ d）是電壓反饋，（ b）、（ c）是電流反饋；另外（ a）、（ c）中反饋支路和輸入支路接在運(yùn)放的同一輸入端，是并聯(lián)反饋，（ b）（ d）中反饋支路和輸入支路接在運(yùn)放的不同輸入端，故是串聯(lián)反饋。 69 第八章 放大電路中的負(fù)反饋 試判斷題 圖所示各電路中反饋的極性和組態(tài)。 解：用瞬時(shí)極性法可確定（ a）是正反，（ b）（ c）（ d）是負(fù)反饋。 試判斷題 圖所示各電路中反饋的極性和組態(tài)，指出反饋元件。（ a）中反饋元件是 RF；（ b）中反饋元件是 RE；（ c）中反饋元件是 RF、 RE1；（ d）中反饋元件是 RF、 RE RE2。 解：直流反饋的反饋元件是 RE RE2 和 RE3，無級間反饋；交流反饋的反饋元件是 RF、CF、 RE1 和 RE3，由瞬時(shí)極性法可確定級間交流反饋是負(fù)反饋； u0=0 時(shí)，反饋不消失，是電流反饋；反饋支路與輸入支路接在晶體管的不同輸入端，故是串聯(lián)反饋，因此，該電路的級間反饋是串聯(lián)電流交流負(fù)反饋。 解：由于電壓負(fù)反饋能穩(wěn)定輸出電壓，降低輸出電阻，電流負(fù)反饋能穩(wěn)定輸出電流，故題 圖中（ d）和題 圖中（ a）、（ b）、（ c）能穩(wěn)定輸出電壓，降低輸出電阻，題 圖中（ b）、（ c）能穩(wěn)定輸出電流。 如果要求當(dāng)負(fù)反饋放大電路的開環(huán)放大倍數(shù)變化 25%時(shí)，其閉環(huán)放大倍數(shù)變化不超過 1%，又要求閉環(huán)放大倍數(shù)為 100，問開環(huán)放大倍數(shù)和反饋系數(shù)應(yīng)選什么值？如果引入的反饋 為電壓并聯(lián)負(fù)反饋，則輸入電阻和輸出電阻如何變化？變化了多少？ 解：由AdAAFAdAff ?? 1 1 可得 +u o+u iU C CC 1C 2C FR FR E 1 R E 3R E 2R B 1R C 1R C 2R C 3C E題 8 . 3 圖 71 1 ??AF， 24?AF 又 1001 ??? AFAA f，故 2500?A ，選 A=2500，則 F= 103，如引入的反饋為電壓并聯(lián)負(fù)反饋，則輸入電阻和輸出電阻均降為原值的 1/25。輸入信號為正弦波， 其有效值為 10mV，輸出信號由基波和二次諧波組成，基波分量有效值為 10V，二次諧波分量有效值為 1V。 判斷題 圖所示電路的反饋組態(tài)，估算電壓放大倍數(shù)，并說明對輸入、輸出電阻的影響。由于運(yùn)放的開環(huán) 放大倍數(shù)很大，AF 遠(yuǎn)大于 1，因此 11 11 Fu f f RAAAA A F A F F R? ? ? ? ? ?? 又由于運(yùn)放的輸入電阻很大，引入串聯(lián)負(fù)反饋后，輸入電阻增大到開環(huán)時(shí)的（ 1+AF）倍，因此，電路的輸入電阻可看作無限大；另外，引入電壓負(fù)反饋后，輸出電阻要降到開環(huán)時(shí)的 1/（ 1+AF），而運(yùn)放的輸出電阻本來就較小，因此，電路的輸出電阻可看作為零。 解：題 圖（ b）是串聯(lián)負(fù)反饋，iRf UUu ?? 2， 由反相輸入端虛 斷可得 )(3224 RRRUU iR ?? 對結(jié)點(diǎn) a 應(yīng)用 KCL 得 432220 1)( RRRRURURU iiL ??? 故 2 3 424()OLuiU R R R RA U R R???? 題 圖（ c）電路為并聯(lián)負(fù)反饋， fi II ? ，由虛短可得 1RUI ii ? ，CEFECEFEeEFEf RURR RIRR RIRR RI 0?????? 由 CEFEi RURR RRU 01 ??可得 10 )1( RRRRUUA CEFiu ??? 題 圖（ d）電路為串聯(lián)負(fù) 反饋 02 22 URR RUUU FRfi ????， 故 20 1 RRUUA Fiu ??? 設(shè)題 中圖（ a）、（ c）電路滿足深度負(fù)反饋條件，試估算其電壓放大倍數(shù)。 解：要降低輸出電阻，應(yīng)引入電壓負(fù)反饋，因此，輸出電壓要從 E 點(diǎn)引出。R CR E+U C CR Bu iR 1 CE題 8 . 1 0 圖A 74 （英文版 ） easily blame, to prevent the broken window effect. Supervise the leading cadres to play an exemplary role, take the lead in the strict implementation of the code and rule , lead to safeguard the solemnity and authority of the party discipline, ensure that the party discipline and the laws and regulations for implementation in place. Throughout the discipline in the daily supervision and management , strengthen supervision and inspection, from the thorough investigation of violations of discipline behavior. Strengthen to key areas, key departments and key projects as well as the masses reflect the concentration of the units and departments for supervision. strengthening supervision, discipline inspection and supervision of cadres to set an example for pliance with the code and rule is a man must be hexyl, blacksmith needs its own hardware. Discipline inspection ans as the executor of the party discipline, and supervisor of the defenders, for its supervision must be more strictly, discipline inspection and supervision of cadres to firmly establish the awareness of Party Constitution, sense of discipline and rules consciousness, politics loyalty, sense obey. Action speak Ji Ordinance to set an example of the 75 regulations of the rule of law, strengthen supervision and accept the supervision of the firmness and consciousness, do ply with and . To firmly establish the discipline must first be disciplined, the supervisor will be subject to the supervision of concept, and consciously safeguard and implement party passes party, take the lead in practicing three strict real strict, so loyal, clean, play. To be good at learning, the Constitution and the code as morality, politics and brought to fruition。 to discipline a ruler, often the control inspection, and consciously in the ideological red line to draw the row Ming Good accumulation is indeed the bottom line, so that the heart has fear, said to have quit, the line has ended. Attached: indifferent to heart, calmly to the table in our life, there are many unpredictable things will happen, some good, some bad things, we cannot control is powerless to stop, but with time, you will find in life sometimes turns out to be not good, some bad things finally turned out to be a good thing, but then we muddy however did not know, this is the life teach us things. 1, life can be plex, can also be simple. Want simple life of precipitation, to have enough time to reflect, to make Bee 76 more perfect. Life is the most important thing is not to win, but the struggle。 not disillusioned after the heart, such as ashes, but experience the storm after the enlightenment。t always take everything back to things, and don39。t want to face, don39。 I am not afraid of the truth to tell the best friend, I39。t 6, when we are in a positive frame of mind, you will find many good things。 life happy and worry, all is you of life attitude, optimistic, good luck。 heart tired, calm. Grow up, mature, this society read. Tired and sad, squat down, to their a hug. Because the world no one can sympathize with you, have mercy on you. You cry, tears is your own。 now want anything, for fear that others know, or like to lose the same. 9, the heart move, everything in the world is followed by birth, Rangrang, important thing is often the most difficult to open one39。 to let strangers people care about your life in the good things, the original is not easy 10, do not blame, do not laugh at who, also don39。 no matter how many grievances, how unfortable, and ultimately to heal themselves or their own, others may got you to fort, but never know your heart is how wanjianchuanxin. 12, ma39。 and an exception is better to give than to what 13, don39。t lose your life and the life, respectively is: the