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OPA2137: No amplification

user5086919
Prodigy 85 points
Part Number: OPA2137

Hi,

I am using OPA2137 in a non inverting configuration.  I have 10Koham in the negative input and 100Koham in the feedback for 11X amplification.  I am using +9V and -9V batteries to power the amplifier.  In order to test the setup I feed the positive input with a 100mV directly from a function generator at frequencies below 1kHz.  I feed both the output and the input signal from the function generator to the scope so I see them both simultaneously.  

The output signal follows nicely the input, centered around 0, but there is no amplification.  In fact the output signal is 20-50 times smaller then the input (100mV).  

What could cause such an effect?

Thank you!

 

  • 0
    TI__Genius 15410 points

    Hello,

    I do not immediately know what might be causing this issue. Below lists a few things to check.

    1. Verify the connections of resistors and op amp pins. If you are using a breadboard to build the circuit make sure the pins of the op amp and resistors are making a good connection with the breadboard.

    2. Since you are using a dual op amp verify that you did not accidently populate some components that should have went to channel A in channel B of the op amp.

    3. Verify the resistor values are correct.

    4. Verify the vertical scale settings on the scope are equal for the input and output channels.

    If after verifying the items above does not fix the issue, please post a screen shot of the scope and your schematic to help us determine what might be causing this issue.

    Thank you,

    Tim Claycomb

  • 0
    TI__Mastermind 49010 points

    Hello,

    If I understand correct, your circuit looks something link this:


    Doing the simulation, we can see the transfer function looks like this:

    Which at 1kHz, is 20.83dB or linearly11.00 V/V .

    Looking at the transient with a peak to peak input of 10mV, I get close to 1Vpp on the output.Which is what we expect.

    Taking a quick look at the datasheet I don't see anything that immediately pops out at me. I have a suspicion it is likely because the O-Scope is attenuating the output. Usually on O-Scope they have an attenuation setting. You may need to adjust this to actually see the correct output. Also if your input seems okay on the O-Scope, use the input probe and take a look at the output. If it is still attenuated then may not be the O-Scope that is the issue.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 85 points

    Thank you Bobby.

    Yes, this is the setup. To make sure it's not the scope I switched between the lines going into the scope. I see the same results.  

    Does the impedance of the scope has anything to do with the results?

     

  • 0 in reply to Tim Claycomb
    Prodigy 85 points

    Thank you Tim,

    Everything is checked.  The wires are welded on a PCB and the device is in a metal box. The schematics is as shown by Bobby below.  

    Regarding #4.  Why have them both on the same scale? 

  • 0 in reply to user5086919
    Prodigy 85 points
    I took the PCB out and rewired the whole thing. The wire connecting the output to the package was not good. It works fine now.
    Thank you for your help!
  • 0 in reply to user5086919
    Prodigy 85 points
    I took the PCB out and rewired the whole thing. The wire connecting the output to the package was not good. It works fine now.
    Thank you for your help!!