internal circuitry 0f 741 op-amp

Discussion in 'The Projects Forum' started by adewale, Apr 8, 2009.

  1. adewale

    Thread Starter New Member

    Apr 8, 2009
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    I urgently need help to find the internal transistors component values of UA741 0p-amp schematic diagram. The resistors values has been given as well as the capacitor but the transistors remain unknown . Alternativell if someone can provide me a completed type of simple operational amplifier shematic diagram with full component values .
     
  2. Wendy

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    Mar 24, 2008
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    If I read your request correctly you are wanting equivalent transistors for the ones inside a 741. I doubt if anyone has ever worked it out, since IC fabrication allows things that even equivalent transistors might not be able to do, mostly in the realm of matched parts. Transistors made on the same die are extremely close to each other on their specs, even though compared to another die those specs can vary widely, as is normal with normal transistor. This is very important for things like current mirrors and differential amplifiers, where transistors are expected to "mirror" the properties of their mate.

    Having said that, making a differential amp out of transistors is easy, there is nothing magic about a 741 design. The subject has come up before, I've seen good designs by some of our senior engineers posted.

    So the question is, what are you trying to do? It helps if we have a background.
     
  3. Audioguru

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    Dec 20, 2007
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    The datasheet of the uA741 from Texas Instruments shows two matched transistors with two collectors and one transistor with four collectors. How can you make them with ordinary transistors or simulate them?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    There are designs out there - http://www.dself.dsl.pipex.com/ampins/discrete/discrop.htm

    I have another from Southwest Technical Products, but can't post it up as it is a croyrighted circuit, and there does not seem to be anyone left to grant permission to use it.

    P.S. I think you can make more than one electrical connection to a collector. I don't want to dig through the catalogs again, but matched pairs for diff amp use are available.
     
  5. Audioguru

    New Member

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    Isn't it nice that the discrete opamp made by Douglas Self has such a high amount of negative feedback that its distortion is fairly low?
    The open-loop gain is very high but the closed-loop gain is only 4.
     
  6. Ron H

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    Apr 14, 2005
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    Here is one that I designed.
     
  7. Wendy

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    Speak of the devil and up he jumps. Just curious, why two current sources on the differental pair.
     
  8. adewale

    Thread Starter New Member

    Apr 8, 2009
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    I have a mini design project to choose a datasheet schematic of a popular op-amp ic and use it to create a fully working multism simulation. Analyse the stages used and create some tests to verify its performance. Please kindly help beefore the deadline date .
     
  9. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    That would appear to be so that the CMRR might be twiddled.

    Eric
     
  10. beenthere

    Retired Moderator

    Apr 20, 2004
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    The CA3140 has an internal schematic in the data sheet. That was a hot op amp about 1980.

    I do wonder if you are going to be able to get details on the internal transistor spec's, though. You might just have to make a guess and see if the simulation lines up with published performance.
     
  11. Ron H

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    Which transistors are you talking about?
     
  12. Wendy

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    Q1 and Q2 are the differential pair, Q3 and Q4 makes one constant current source, and Q5 and Q6 make the other.
     
  13. Ron H

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    Q6 is the tail current for the diff pair (which I'm sure you know). Call this current It. Q5 is feedback biasing for Q6.
    Q3 and Q4 form a current mirror. When the input is balanced, It/2 flows through the collectors of Q1 and Q2 (ignoring base currents). Due to the current mirror, It/2 also flows through Q4. Any differential current due to input imbalance will flow into the base of Q7. Obviously, this base current can only flow in one direction, so a small input offset voltage must exist to provide Q7 bias current. This can be nulled out by the pot R10. R10 can also compensate for mismatches in Q1 and Q2, and in Q3 and Q4. The input offset voltage will change slightly with temperature.
    For better matching, use a CA3046 for Q1 and Q2. The remaining trannies in the 3046 can be used for Q5, Q6, and Q8. If you're going to use an IC, you might as well use an IC op amp.:rolleyes:
     
  14. pilko

    Active Member

    Dec 8, 2008
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    Is this what you're looking for?It opens in LTSpice SWCAD3
     
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