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Original question:

OPA857: Output voltage noise

TINA/Spice/OPA857: OPA857

harini burra
Prodigy 120 points
Part Number: OPA857
Other Parts Discussed in Thread: TINA-TI, , OPA847

Tool/software: TINA-TI or Spice Models

hi,

i have generated a Gaussian pulse with pulse width of 10ns in matlab and generated a .WAV file.

after generating the .WAV file and while giving the .WAV file as input to the schematic design of OPA857 the input gaussian wave generated   time axis is changing into milliseconds during the schematic simulations 

please help me how to solve this problem.

  • 0
    TI__Genius 16735 points
    Hello,

    Can you attach the .WAV file as well as your schematic so I can replicate the error. Are you certain that the .WAV file is 10ns and not 10ms?

    Thanks!
    -Karan
  • 0 in reply to Karan Kotadia
    Prodigy 120 points

    design1.TSCClick here to play this audio cliphello,

    yes the .WAV file is for 10ns.

    i am using TI Designs: OPA857 Ultralow-Noise, Wideband, Selectable-Feedback Resistance Transimpedance Amplifier document for designing OPA857

  • 0 in reply to harini burra
    Prodigy 120 points

    hi,

    do you have any update??

  • 0
    Guru 140200 points
    Hi Harini,

    why not using a pulse shaper?

    www.dnp.fmph.uniba.sk/.../el2.htm

    Kai
  • 0 in reply to harini burra
    Guru 48395 points

    I looked at your TINA file for the OPA847, you do know there are internal feedback R's I assume - total gain for your file is 2.8kohm as you have it set for 4.5kohm internal feedback. 

  • 0 in reply to harini burra
    Guru 140200 points

    Hi Harini,

    this is how your wav_file looks to me:

    harini.TSC

    Kai

  • 0 in reply to kai klaas69
    Guru 140200 points

    Hi Harini,

    and this would be the pulse response of your circuit (the Gaussian pulse normalized to 100µA):

    harini1.TSC

    Kai

  • 0 in reply to kai klaas69
    Prodigy 120 points

    hi,

    thank you for your suggestion

    i tried using pulse shaper for generating Gaussian pulse, i have generated a Gaussian pulse for 100nV amplitude using voltage  source.

    but when i am using a current source input there is no output response

    please help me to solve this problem as my input to the OPA857 is through a current source

    my reference for the complete design is  TI Designs:Optical Front-End System Reference Design

  • 0 in reply to kai klaas69
    Prodigy 120 points
    hi,
    thank you for your reply
    how can i modify more to this design so that i can achieve my Gaussian pulse amplitude of 100nA and also my Gaussian pulse width of 10ns
  • 0 in reply to harini burra
    Guru 140200 points

    Hi Harini,

    I only "see" the current in the simulation when it produces a voltage drop across the shunt resistor. So, the current is there. Take my simulation file and play with it.

    The amplitude of Gaussian pulse can be changed in this window:

    To change the width of Gaussian pulse I think you must create a new WAV_file.

    Kai