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TINA/Spice/OPA376: noise model of OPA376 inside TINA

Yuan Tan63
Expert 3280 points
Part Number: OPA376
Other Parts Discussed in Thread: TINA-TI,

Tool/software: TINA-TI or Spice Models

Hi,

this is the simulation circuit.

when R1=1k, the result is :

the same with curve in datasheet:

but when R1=1M, it seems like that:

why and is it in line with reality?

thanks!

  • 0
    Guru 140200 points

    Hi Yuan,

    the reason for the peak is very simple: WIth the 1M feedback resistor the OPAmp becomes unstable and shows a huge peak in the frequency response, exactly where your noise peak is located.

    The 1M feedback resistor in combination with the input capacitance of OPA376 produces a heavy phase lag in the feedback loop which totally erodes the noise margin. That's the cause of instability and noise peak.

    Kai

  • 0 in reply to kai klaas69
    TI__Guru* 93105 points
    Hi Yuan,

    Kai explained the OPA376 noise peak issue very well. Do you need anything more? If you are satisfied with the response, please close this E2E inquiry.

    Regards, Thomas
    Precision Amplifiers Applications Engineering