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Original question:

TINA/Spice/OPA627-DIE: OPA627

TINA/Spice/OPA627-DIE: OPA627

Jubayer Jalil
Prodigy 200 points

Part Number: OPA627-DIE

Tool/software: TINA-TI or Spice Models

Hi,

I have simulated the attached  diagram for noise analysis. Though, 20 Gohms resistance has been attached at the input, it did not contribute as a thermal noise in the overall output noise 53.44n @20kHz. This output noise of 53.44n @20kHz is obtained while it is run without 20 Gohms resistance. Is it test setup problem or software limitations?

Look forward to hearing from you soon. 

Kind reagrds

1411.6470.Inverting mode.TSC

  • 0
    TI__Mastermind 38065 points

    Jubayer,

    I was unable to open your file with TINA.
    Would you try to upload it to this thread again?
    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 200 points

    2475.Inverting mode.TSC

    Hi,

    I have simulated the attached  diagram for noise analysis. Though, 20 Gohms resistance has been attached at the input, it did not contribute as a thermal noise in the overall output noise 53.44n @20kHz. This output noise of 53.44n @20kHz is obtained while it is run without 20 Gohms resistance. Is it test setup problem or software limitations?

    Look forward to hearing from you soon. 

    Kind regardsDoc2.docx

  • 0 in reply to Jubayer Jalil
    TI__Mastermind 38065 points

    Jubayer,

    I built up a circuit based on the Word document you provided.
    The 10G resistor on the input will contribute no noise because the signal source in parallel with it will conduct the resistor noise to AC ground.
    That leaves the feedback resistor and the op amp model to as noise contributors. To see if the model & simulator are okay, we will do some approximate noise calculations and compare the results to simulations.

    The first step is to look at just the op amp noise interacting with the (noiseless) capacitors and the 1G feedback resistor.
    The 1G feedback R is made noiseless by setting its absolute temp to -273.15C. This results in the output noise plot shown in the first plot below.
    The first plot shows a max output noise amplitude of 1.6uV/rt(Hz).
    It turns out the major output noise contributor is the input current noise interacting with the large impedances of the external C's and R.
    Using the noise parameters from the datasheet, an approximate calculation predicts about 2uV/rt(Hz) of output noise.
    This calculation ignored the op amp's input C's and R's. If they were included, it would lower the max noise to be closer to the simulated result of 1.6uV/rt(Hz).
    So an approximate analysis of an ideal case (noiseless feedback resistor) gives results that somewhat agree with simulation.

    Next, the 1G feedback resistor is made noisy by setting its absolute temp to 27C. It should contribute 4uV/rt(Hz) to the output noise.
    Combining the approximated current noise (2uV) at the output with the 4uV feedback resistor noise predicts about 4.4uV/rt(Hz) of total output noise.
    The second plot below shows a simulated max output noise of 4.37uV/rt(Hz), which is pretty close to our approximate calculations.
    So it looks like the model and simulator are giving results that are close to some approximate calculations.

    I hope this helps. Please let me know if you have any more questions.
    Regards,
    John

    OutNoiseNoiselessRF.emf

    OutNoiseNoisyRF.emf

  • 0 in reply to John Miller - Sensing
    Prodigy 200 points

    Dear Mr. John,

    Thanks for your answer. I appreciate your cooperation in this regard.

    I have attached another  file of this circuit where Fig 1 cannot simulate in noise analysis whereas Fig 2 can.

    Can you please help me to sort it out?

    Thanks in advance.

    regards

    JubayerDoc3.docx

  • 0 in reply to Jubayer Jalil
    TI__Mastermind 38065 points

    Jubayer,

    I am glad to help. What problems are you having with the circuit?

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    TI__Mastermind 38065 points

    Jubayer,

    Two documents have been uploaded related to your questions.
    One is Doc3.docx in this thread, and the other is 5280.4666.Doc3.docx in another thread.
    They look like the same circuit, or am I missing something?

    Regards,
    John

  • 0 in reply to John Miller - Sensing
    Prodigy 200 points

    Dear Mr. John,

    Yes, they are same circuits in different files!

    You can reply any of the threads.

    Kind regards

    Jubayer