Analysis of given circiut?. is it an OPAMP? explain if you answer is yes.

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Moazza Sultan said:
is it an OPAMP?
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No, it's not.

To turn it into an opamp:
  • Remove Q7 from the circuit.
  • Connect the collector of Q8 to the collector of Q9 and the output.
  • Disconnect the base of Q8 from the bases of Q5 and Q6, and connect it to the collectors of Q2 and Q6 instead.
 

Looks like a partly failed attempt to design an OP. Only input stage Q1/Q2 is working, output stage Q7 is not working, it's permanently in saturation, providing no gain.
 

To turn it into an opamp:
  • Remove Q7 from the circuit.
  • Connect the collector of Q8 to the collector of Q9 and the output.
  • Disconnect the base of Q8 from the bases of Q5 and Q6, and connect it to the collectors of Q2 and Q6 instead.

    Why should i do all that ? reasons?
    I need to explain them to my teacher.

    I try the changes you mention, but Vbe of Q8 becomes 0.44 V

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    What are the necessary things to design the OPAMP?

    - - - Updated - - -
 

After making the changes, the circuit should look like this:



Moazza Sultan said:
Why should i do all that ?
Click to expand...
To fix the circuit.

Moazza Sultan said:
reasons?
Click to expand...
Because the circuit you showed doesn't work.

Moazza Sultan said:
I try the changes you mention, but Vbe of Q8 becomes 0.44 V
Click to expand...
Maybe you ran the simulation with no input and no feedback. The circuit has a small DC input offset.

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Moazza Sultan said:
What are the necessary things to design the OPAMP?
Click to expand...
First you need to understand what an opamp is supposed to do. Then you can design a circuit to do that. You also need to understand how transistors work.

From Wikipedia:
 

No. It can work with a low supply voltage, but the quiescent current is too high for it to be called a low power opamp.

BTW, it's not unity-gain stable either. That means if you use it in an amplifier circuit with low voltage gain, it will oscillate at high frequency. To fix that, you need to connect a small capacitor (e.g. 1nF) between the base and collector of Q8.
 

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