op amp design

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prescott2006

New Member

• Oct 4, 2009

• #1

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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Last edited: Oct 4, 2009

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BrownOut

Banned

• Oct 4, 2009

• #2

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.

 

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prescott2006

New Member

• Oct 4, 2009

• #3

by first stage u which part in the circuit?and the connection is for measure open loop gain?

 

B

BrownOut

Banned

• Oct 4, 2009

• #4

Are you serious? You don't know what the first stage of your amplifier design is? Do you know where the input and output are? Also this: Measure Open Loop Gain

 

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prescott2006

New Member

• Oct 4, 2009

• #5

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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• urt.jpg

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B

BrownOut

Banned

• Oct 4, 2009

• #6

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.

 

Last edited: Oct 4, 2009

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prescott2006

New Member

• Oct 4, 2009

• #7

what mean by operating voltage not correct?there are no connection between q7 and q5?

 

B

BrownOut

Banned

• Oct 4, 2009

• #8

prescott2006 said:

there are no connection between q7 and q5?

Click to expand...

There should be.

 

audioguru

Well-Known Member

Most Helpful Member

• Oct 4, 2009

• #9

You negative -15V power supply is wrongly shown as a positive +15V supply.

 

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prescott2006

New Member

• Oct 4, 2009

• #10

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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prescott2006

New Member

• Oct 4, 2009

• #11

is there wrongly shown?but it show -15V at there.

 

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BrownOut

Banned

• Oct 4, 2009

• #12

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

 

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prescott2006

New Member

• Oct 4, 2009

• #13

so how can i make the circuit to work in real world?sorry to ask so many questions.

 

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BrownOut

Banned

• Oct 4, 2009

• #14

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.

 

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prescott2006

New Member

• Oct 4, 2009

• #15

what is the smallest ac source in real world?

 

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BrownOut

Banned

• Oct 4, 2009

• #16

Not small enough to test open loop gain.

 

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prescott2006

New Member

• Oct 4, 2009

• #17

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

 

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prescott2006

New Member

• Oct 4, 2009

• #18

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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Last edited: Oct 4, 2009

B

BrownOut

Banned

• Oct 4, 2009

• #19

CONNECT VEE CORRECTLY!!!!

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

 

Last edited: Oct 4, 2009

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prescott2006

New Member

• Oct 4, 2009

• #20

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?