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what do you mean by feedback circuit biasing?

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diaryrashid

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hello...can someone tell me what do you mean by feedback circuit biasing?

thanx
 

goldsmith

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hello...can someone tell me what do you mean by feedback circuit biasing?
Hi Diary Rashid
may i ask you where you saw such a sentence , please ? thus i think i can help you . but now your question is a bit unclear !
Best Wishes
Goldsmith
 

LvW

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hello...can someone tell me what do you mean by feedback circuit biasing?
thanx
In many cases negative dc feedback is applied (in amplifiers and control loops) in order to fix and stabilize the dc operating point.
Simple example: Opamps are not operated open-loop but always with a resistive feedback. Without this negative feedback no operation point within the linear transfer characteristic of the devive is possible.
Of course, at the same time this feedback also determines the signal gain.
As another example, also the emitter resistor Re in a common emitter BJT stage provides dc feedback and is part of the biasing circuitry.
 

T3STY

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That's the feedback system that is used in most looped circuits. In circuits involving amplification you have to control how much amplification to get from the circuit and you need a feedback reaction to actually limit (or "to feedback") the amplification. What happens in those circuits is that (assuming an open-loop circuit - not feedbacked) even when it arrives to the saturation point (Vs) it still wants to amplify (up to infinite) asking for more and more current... until the components will get enough and physically break. The feedback though always ensures that
In + ( -Out) = k
which means that the input (In) in an amplifier summed to the (negative) feedback received from the amplifier, has a constant value result that the amplifier will try to reach - either by amplifying the input (if In < k) or by attenuating it (if In > k) - without risking to break during usage*.
In analog electronics I'm totally ignorant, but I assume that the emitter resistor used for BJT transistors is there for the same reason as the feedback resistor in op-amp circuits, limiting amplification to avoid saturation and component break. Though, I'd wait for someone else to tell this right.

*unless you miscalculate component values which makes k too high for the amplifier to work safely or you're working in a hostile environment for the components. You should always ensure the amplifier works under the limits described in the datasheet, as well as for the other components.
 

LvW

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In analog electronics I'm totally ignorant, but I assume that the emitter resistor used for BJT transistors is there for the same reason as the feedback resistor in op-amp circuits, limiting amplification to avoid saturation and component break. Though, I'd wait for someone else to tell this right.
Saturation cannot be "avoided" - it happens at another input level, that`s all.
However, the question was related to biasing- not to amplification or saturation.
 

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