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Take beta = 99.

I analysed this circuit using first considering this circuit as feedback circuit with shunt-shunt type of feedback and then did the same analysis considering that the circuit is a common emitter amplifier ; i.e. I pretended that I don't know feedback circuits and followed the basic approach of nodal analysis followed in small signal analysis.

I got different results for small signal Voltage gain from both type of analysis. Obviously, the analysis without considering the network as feed back is correct, but I want to ask that how to realize that I should solve using basic approach neglecting feedback concepts.

I am having vibe that it has to do something with approximations taken while feedback analysis that

[Y12]A<<[Y12]B

[Y21]A>>[Y21]B

are not appropriately satisfied in below circuit. That is why I got different answers. Please clear up this concept. My calculations for Voltage gain

enter image description here

For calculating trans resistance gain enter image description here

Why I am getting different answers for trans resistance gain using different approach?

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  • \$\begingroup\$ The gain will be around \$A_V \approx gm*RC \approx 0.28S*510\Omega \approx 143 V/V\$ \$\endgroup\$
    – G36
    Jun 18, 2019 at 13:48
  • \$\begingroup\$ @G36 I am also getting the same answer by small signal analysis but after doing analysis considering circuit as an example of shunt-shunt feedback topology I get 74 as voltage gain.I am having problem in understanding that why there is so much difference in result. \$\endgroup\$ Jun 18, 2019 at 13:56
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    \$\begingroup\$ Your, feedback analysis is wrong. Because Vin (ideal voltage source) will kill the feedback effect. \$\endgroup\$
    – G36
    Jun 18, 2019 at 14:05
  • \$\begingroup\$ @G36 thanks for pointing out but I am also getting different answers when i calculate trans resistance gain using two approach see edited \$\endgroup\$ Jun 18, 2019 at 14:42

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