The circuit that retreat Ou is the peculiar circuit in multistage amplifier, also be the circuit that must install. The action of the circuit that retreat Ou is to eliminate various amplifier mutual the harmful interference between. The circuit that retreat Ou connects standing buy to be between two class amplifier, only so the ability in multistage amplifier has the circuit that retreat Ou. Before the analysis retreats principle of Ou circuit job, should understand first why should retreat Ou circuit in the setting in multistage amplifier, how to arise between various amplifier namely hand in between pernicious form even.

 

 

Well-known, volts d.c. + V carries right communicating and character is ground connection, this is good case, take no account of the internal resistance R0 of power source namely. Actually direct current source is put in internal resistance, if pursue,1 is shown. Can see from inside circuit, direct current source is inside dotted line casing, it is established ties by voltage source E and internal resistance R0 and become, when electric current has sorted this one direct current source, have on internal resistance R0 pressure fall, this is pressed falling is in causing circuit harmful reach connected prime cause place.

 

Graph circuit of equivalent of 1 direct current source

 

 

Alleged handing in is to point to the phenomenon of a kind of self-excitation that produces in multistage amplifier repeatedly.

 

By the character of common emitter amplifier knowable, the output signal voltage of this kind of amplifier is phasic phasic and as contrary as input signal voltage. One class common emitter amplifier is phasic to inputting signal if be two class,turn over photograph 180°; common emitter amplifier, can turn over to inputting signal 360° . If pass two level,the input that the signal after common emitter amplifier magnifies strung together amplifier of the first class through power source internal resistance is carried, this is feedbacking namely, it is multistage amplifier between harmful hand in even, this is unallowed in multistage amplifier, ou circuit should be retreated between setting class so.

 

Explain the working principle that Ou circuit retreats in multistage amplifier to go to the lavatory, to in an attempt to shows two class amplifier 2 times to be exemple.

 

Graph the circuit retreating Ou in 2 multistage amplifier

 

Basically explain repeatedly about be being handed in between the class between multistage amplifier a few following.

 

(1)VT1 and VT2 form the first class and amplifier of the 2nd class respectively, this two class are common emitter amplifier. The input signal voltage according to common emitter amplifier and output signal voltage are phasic and characteristic knowable, the output signal voltage of this kind of amplifier is phasic phasic and as contrary as input signal voltage.

 

(2) did not retreat Ou capacitance C2 in circuit suppose, the signal voltage that assumes some goes up in VT1 base for an instant is in increase, it is “+” namely, if circuit pursues,be shown. Because the output signal voltage of common emitter amplifier is phasic phasic and as contrary as input signal voltage, the signal voltage on such VT1 collector is phasic for “-” , voltage of VT2 base signal is phasic do not move for C3 of “-”(coupling capacitance signal is phasic) , the signal voltage on VT2 collector is phasic output signal voltage and input signal voltage for amplifier of “+”(common emitter phasic and contrary) .

 

(3) is put inevitably in internal resistance R0 as a result of direct current source, when electric current of VT2 collector signal has shed R0, signal pressing arose to fall on its, namely the B dot in circuit has signal voltage, and phasic for “+” .

 

(The R4 of classics of this one signal that the B in 4) circuit nods increases A point, voltage of A dot signal is phasic also be “+” , this signal is added to VT1 base again through R1, make voltage of VT1 base signal bigger, repass make a present of of a series of positive and negative of afore-mentioned circuit, the signal that makes VT1 medium is very big and generation self-excitation, occurrence howl cry, this is multistage amplifier in harmful hand in the circuit howl that causes repeatedly to make an appearance.

 

 

Basically explain about retreating the working principle of Ou circuit a few following.

 

(After 1) is joining C2 of the capacitance that retreat Ou, the signal of positive electrode sex on dot of the A in circuit is carried to the ground by C2 bypass, and cannot increase VT1 base through resistor R1, such multistage cannot produce make a present of of positive and negative in amplifier, also do not have class between hand in even the phenomenon, achieve eliminate class harmful meet connected goal.

 

(After R4 of the resistor that retreat Ou is being joined in 2) circuit, can improve the result that retreat Ou further, because circuit is medium,the component that the signal tension that B hints is made by R4 and C2 pressed circuit to undertake attenuation, even smaller than joining the A when R4 to hint signal tension, it is better to remove Ou effect so.

 

(3) retreats Ou resistor R4 to divide have outside enhancing the effect that removes Ou, amplifier of the class before still be offers dc job voltage, after dc electric current has flowed to retreat Ou resistor R4, have on resistor R4 pressure fall, the dc job voltage of circuit of the class before was being reduced so.

 

Brief summary

(In 1) multistage amplifier, at least common emitter amplifier should set every two class to retreat Ou circuit. Because of each class common emitter amplifier is turned over to signal voltage, what two class amplifier undertakes twice turning over voltage of the signal after the photograph is phasic become again inphase, feedbacking between class of this easy generation and appear self-excitation. So, the knaggy circuit that retreat Ou is set in multistage amplifier.

 

(2) retreats Ou capacitance besides having the effect that retreat Ou, to dc working voltage still has the effect of filter wave.