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What is the input current noise density of OPA171?

Other Parts Discussed in Thread: OPA171, OPA627

Hi,

Our customers are trying to calculate the output noise of the OPA171.

The data sheet of the OPA171, does not contain the input current noise density.

What is the input current noise density of OPA171?


Best Regards,

Hiroaki Masumoto

  • Masumoto-san,

    JFET input op amps have extremely low input current noise density. Typically, it runs from a little under 1 fA/ rt-Hz, to a little over 2 fA/ rt-Hz for JFET input op amps, as a class of op amps. It is difficult to accurately measure because of its very low level.

    In the case of the OPA171 the decision was made not to measure it and provide a datasheet number. This isn't necessarily a bad decision because the contribution of current noise to the overall amplifier noise is overwhelmed by the input voltage noise density contribution. 

    To illustrate that point, see a page from a noise analysis done on the OPA627 JFET input op amp. See how high the voltage noise is compared to the current noise. The voltage and current noise were converted to RMS in a previous slide.

    Regards, Thomas

    PA - Linear Applications Engineering

     

  • Hi Thomas Kuehl-san

    Thank you for your help.

    I understand the contents of the reply.

    The input current noise density of OPA171 looks very small value.

    I will inform this information to customers.

    Regards,
    Hiroaki Masumoto