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op amp design

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prescott2006

New Member
i am designing an opamp to obtain open lop gain of 4000.i arrive at the second one.can somebody provide me the real circuit to replace the current source?and can you show me the connection to measure open loop gain?

circuit source: Ron H from allaboutcircuits.com
 

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  • DSC00860.jpg
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  • op amp with higher gain.JPG
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BrownOut

Banned
The output of your first stage should be connected to Q7/Q2. For the current, look up "current mirror." That method only works well as an integrated circuit, or you can find a matching transistor pair.
 

prescott2006

New Member
i connect like this to measure open loop gain ,is it correct?but i only manage get gain of 100 (7/0.0707).can you help me check whether the circuit is correct or not?
 

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BrownOut

Banned
Your test method totally won't work. Your operating voltage is not applied correctly. Also, there seems to be a connection missing betweeen Q7 and Q5.
 
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audioguru

Well-Known Member
Most Helpful Member
You negative -15V power supply is wrongly shown as a positive +15V supply.
 

prescott2006

New Member
sorry,my bad.there really got connection.i simulate it and get such value.29.16m/7.07u=4124,so the circuit is correct for gain 4000?
 

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  • check.jpg
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BrownOut

Banned
It only works through the "magic" of simulation. This would never work in a real circuit.
 

BrownOut

Banned
First, connect the operating voltage correctly. Look over this discussion to learn how. The simulation works, but in the real world, a 10uV source doesn't exist. Use the link I provided to see how to do this correctly. If this is just an exercise in "theoritical" imaginary electronics, you're probably done.
 

prescott2006

New Member
ok,then refer to your attachment.i just need to connect the same connection into my circuit?the value of the resistor also same?
 

prescott2006

New Member
why i measure the v out is -1.2m while vx is 475 m.the v out not suppose to be larger than the vx?

circuit source: Ron H from allaboutcircuits.com
 

Attachments

  • simple discrete op amp.asc
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BrownOut

Banned
CONNECT VEE CORRECTLY!!!!

As you continue to refuse to correct this problem, you'll never get anything to work.
 
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prescott2006

New Member
i really not sure why my vee got problem.it is connected to -15v.i am really a beginner,maybe i cannot follow your meaning,can you modify the circuit for me?
 
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