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Equivalent feed back model transformation

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yefj

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Hello i am using the two stages amplifier shown bellow into the transimpedance feedback system shown bellow.
if the system shown bellow i have miiler capacitor and feedback ressistor
how do i break them into the system shown in the end?
Thanks.

1.JPG

2.JPG
 

The problem is about extracting Zi, Zo and av from your circuit. As mentioned in your previous thread, an OTA could be better modelled as a current source than a voltage source. But formally, you can still extract a Zo and av.
 

yes , i have modeled it as current source but how to handle miller capacitor in this system?
Thanks.
 

Miller capacitor is inside the OP, it modifies av and Zo.
 

Hello, Thank you very much, i will try to add the miller effect as you said regarding the capactior.
Regarding the feedback loop ,Why it couldnt be decomposed just like the capacitor we talked about now?
Why miller laws are not applied in the case of the feedback loop ressistor and instead we do a copy of the ressistor both in the input stage and ouptut stage as shown in the diagram in the first post?
Thanks
 

yes , i have modeled it as current source but how to handle miller capacitor in this system?
Thanks.

Why don't you just use return ratio for the loop? Then you don't have to bother with the miller cap as it effect will be included in the ac gain of the OTA.
 

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