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I'm studying analog electronics circuit with feedback.

I see that, during analysis, a useful abstraction over the schematic is the block diagram in control theory style, but I stuggle in deriving it from the schematic.

Also, I found a lot of textbooks describing the problem either from electronics point of view or from control theory's one.

Does anyone have a good recommendation for material which attempts to fill the gap and derive the block diagram starting from the circuit?

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  • \$\begingroup\$ I recall Schaums Outline. Perhaps a used book-store has copies. Or online. \$\endgroup\$ – analogsystemsrf May 18 at 10:30
  • \$\begingroup\$ Hi @analogsystemsrf thanks for the reply. Do you remember the title of the volume? \$\endgroup\$ – a_bet May 18 at 10:35
  • \$\begingroup\$ "Control systems" is a free PDF download \$\endgroup\$ – analogsystemsrf May 18 at 11:39
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    \$\begingroup\$ Does it seem to you that there's something in particular, specific, that won't allow you to go from schematics to control blocks? I mean, if there's an analog circuit you're analyzing, you might want to share it with us along with what you've done and what stops you. Because often, at its heart, the link between electronics and control theory are just Kirchhoff's laws and choosing your inputs and your output(s). \$\endgroup\$ – edmz May 18 at 11:59
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In principle, you have nothing to do than to convert known formulas (relationships) into corresponding blocks.

Here is a basic example how to draw a closed-loop block diagram for the feedback effect caused by the emitter resistor Re in the classical BJT amplifier stage:

vbe=vb-ve with ve=ieRe and ie=ge*vbe (emitter related transconductance ge=Ie/Vt)

Hence, the input summing block makes (vb-ve) and the output (vbe) enters the closed loop consisting of the block [ge] and the block [Re].

Comment 1: In control theory it is common that blocks do not change units (amplifiers, controllers, attenuators,...). However, this is not a requirement. In the above example, we have a unit change from voltage to current and then from current back to voltage.

Comment 2: The above example shows that such a construction of a block diagram gives a visualization of a feedback loop - even if such a loop cannot be identified in the circuit diagram.

enter image description here

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