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How is the gain set in a closed loop system?

Is it better to use an open loop or closed loop amplifier?

  • It is usually better to achieve some necessary closed loop gain with an amplifier that has huge open loop gain, and lots of negative feedback, than to use a lower gain amplifier and less negative feedback (or even just an amplifier with no negative feedback which happens to have that gain open loop).

What is the GBW of a closed loop system?

  • In a closed loop system, the gain is set by the feedback network, provided that the open loop gain is high (see answer 3 as well). No matter the closed loop gain level, the product between gain and bandwidth, or the gain bandwidth product (GBW) is constant. Therefore, the GBW in this case is.

Does the feedback factor affect the closed loop gain?

  • A3: Yes it does. The first answer shows that the feedback factor is used in the closed loop gain calculation. Also, if the open loop gain is high, the feedback factor determines the closed loop gain at DC and in band. Indeed, let’s show this by rewriting equation (3) at DC.

image-How is the gain set in a closed loop system?
image-How is the gain set in a closed loop system?
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