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OPA2180 and OPA2188 noise voltage

George Hamby
Prodigy 70 points
Other Parts Discussed in Thread: OPA2188, OPA2180

The data sheet noise voltage for the OPA2180 is listed as 10nV/rtHz.  The noise voltage for the OPA2188 is listed as 8.8nV/rtHz.  However the data sheets for the OPA2180 figure 6 and the OPA2188 figure 15 show essentially identical noise spectral density characteristics.  Can anyone explain this discrepancy? 

  • 0
    TI__Guru 60610 points
    George,

    The input voltage noise spectral density is inversely proportional to the input current biasing the input differential pair, Itail. Since in case of OPA2180 the variation in the IQ (and thus Itail) is greater than in case of OPA2188, as the Itail gets smaller the input voltage noise becomes larger (btw, Fig 6 in OPA2180 datasheet does not properly show this difference). Also, keep in mind that graphs show only typical values and there may be as much as +/-25% wafer process related variation in the broadband noise due to variation in Itail current.
  • 0 in reply to Marek Lis
    Prodigy 70 points

    Marek,

    I have noticed that the OPA2180 and OPA2188 have many similar specifications.  I have not seen any specific

    information that the OPA2180 and OPA2188 are identical silicon, and, that the OPA2188 is a selected higher

    grade over the OPA2180.  If that is correct, can I assume that typically the OPA2188 will have a lower noise voltage

    compared to the OPA2180?  This would explain the 10nV/rtHz and 8.8nV/rtHz specification differences.

    George