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

[Moazza Sultan]

Explain the given Circuit. is it an OPAMP?
Where's the input stage and output stage?

 

[godfreyl]

is it an OPAMP?

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.

 

[FvM]

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.

 

[Moazza Sultan]

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
  
  - - - Updated - - -
  
  What are the necessary things to design the OPAMP?
  
  - - - Updated - - -

 

[godfreyl]

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

Why should i do all that ?

To fix the circuit.

reasons?

Because the circuit you showed doesn't work.

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

Maybe you ran the simulation with no input and no feedback. The circuit has a small DC input offset.

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What are the necessary things to design the OPAMP?

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:

An operational amplifier (op-amp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. An op-amp produces an output voltage that is typically hundreds of thousands of times larger than the voltage difference between its input terminals.

 

[Moazza Sultan]

is it a low power OPAMP?

 

[godfreyl]

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.