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[SOLVED] Understanding LM741 Op-Amp

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dzafar

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Hi!

I am trying to understand the "purpose" of different transistors in LM741. In the figure below,

- I understand that Q1 and Q2 form a differential pair.
- Q5, Q6 along with R1 and R2 for the resistor-ratioed current mirror. I am guessing their function is to act as load. Is that correct?
- Q7 is the base current compensating transistor, added to reduce mismatch. Is that correct?
- R3, the current shunting resistor, is to make Q7 operate at the same current as Q5 and Q6.

- Question 1: Is Q8 the biasing transistor?
- Question 2: What does Q3 and Q4 do?


Thanks for all the help :)

Screen Shot 2017-04-01 at 6.51.48 PM.png
 

Question 1. Ans:
Here in the above circuit, transistor Q8 with transistor Q9 forms current mirror circuit. (generally the current mirror consist of two matched transistor with their base and emitter connected together where one of these transistor connected as diode by sorting its collector and base.)
Question 2. Ans:
the transistors Q1 – Q3, that is Q2 – Q4 are in complementary Cascade arrangement. This pair also helps to create virtual ground between inverting and non-inverting inputs in the case of differential mode input signal because it's base in not directly grounded.
Hope it will help you.
 
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    dzafar

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Suggest to review the detailed analysis of 741 OP in Gray/Hurst/Lewis/Meyer Analysis and design of analog integrated circuits.
 
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    dzafar

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The lousy old 741 opamp is 48 years old. Modern opamps have much better performance and a completely different design. Maybe this is school homework?
 

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