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I'm confused between whether this is voltage or current mixing. I'm thinking it is current mixing since the input current is subtracted from the source current. But why cant it be voltage since Rb is connected in series with the input loop ?

  • \$\begingroup\$ Your circuit makes no sense, there's no supply, there is no feedback loop. There could be local feedback if the circuit was drawn in a working state but it isn't. \$\endgroup\$ – Bimpelrekkie Nov 25 '16 at 12:10
  • \$\begingroup\$ Normally "feedback" comes from feeding something back, that is output to the input, I can't find it \$\endgroup\$ – PlasmaHH Nov 25 '16 at 12:44
  • \$\begingroup\$ I know its incomplete. I just wanted to clarify the mixing part which is the input side \$\endgroup\$ – Deadshot Nov 25 '16 at 15:17

OK, I know what you mean - in spite of an uncomplete circuit diagram. As you can see, the feedback path and the input path meet in a node which is common to all 3 resistors. In this node, two currents are superimposed - hence, we have "current feedback".

From general feedback theory we know that the input impedance is reduced in case of current feedback (in contrast to voltage feedback). As can be seen, this is the case for your circuit (Miller effect). This is another indication for current feedback.

At the same time, the resistor RE provides voltage feedback (the emitter voltage VE determines the controlling voltage VB-VE=VBE).

However, the question remains, if the whole scheme (current and voltage feedback within one stage) makes much sense. But that`s another question.


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