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OPA695: Input Voltage Noise at <1KHz

Jejomar Ildefonso
Expert 8590 points
Part Number: OPA695
Other Parts Discussed in Thread: LMH6702, THS3491

Hi Team,

Figure 13 in the datasheet shows the input voltage noise characteristics of OPA695 from 1kHz to 100MHz. Our customer would like to request for its input voltage noise characteristics from 0.1Hz to 1kHz. Is this information available?


Thanks in advance!


Kind Regards,

Jejomar

  • +1
    TI__Expert 3620 points

    Hi Jejomar,

    Looks like the spice model will give you the test circuit behavior for the max spec over temp (~2.9 nV/rtHz) so this should be your worst case scenario (file attached):
    OPA695 Noise.TSC

    Best,
    Sam

  • 0 in reply to Sam Burnett
    Guru 47485 points

    Morning Sam and Jejomar, 

    Your sim was for total output noise including a large inverting current noise contribution - just move the meter to the inverting node to show just the voltage noise in the model, And of course this is just the model, not actually matching figure 13, that model shows 2.14nV flat vs 1.7nV in the datasheet, and a 1/f at 223Hz vs 1kHz in the plot in the datasheet - I suppuse you could perhaps fix the model to match Figure 13 - also, what gets into the datasheet is a single part - there is in fact quite a lot of variation part to part in this lower F rfange. 

  • +1 in reply to Michael Steffes
    Guru 47485 points

    Incidentally, the very similar LMH6702 part shows data going down a little lower, 

    And you could just take the OPA695 1.7nV flat and 1kHz 1/f in the datasheet plot and generate the ideal down to 0.1Hz from that. - which I did here modifying the THS3491 data plot, but the original sim Sam did is also important - to note how much the inverting current noise will contribute to total output noise

  • 0
    Guru 140200 points

    Hi Jejomar,

    not publishing any low frequency noise specs <1kHz in the datasheet of OPA695 could also mean, that the OPA695 is showing huge manufacturing tolerances referring to low frequency noise. So if you plan to use the OPAmp in an application where the noise performance down to 0.1Hz is important, I would go for an OPAmp which actually shows low noise specs in the datasheet.

    Kai

  • 0 in reply to kai klaas69
    Guru 47485 points

    Well Actually Kai, having done the OPA695 plots, I can tell you these plots are more often constrained by the high pass filter built into the input of the noise preamp used to protect the spectrum analyzer - Later, we built them to go down to 100Hz which more matched up with what the HP3488 spectrum analyzer could do. - Not really trying to hide anything, but there is indeed part to part variation on this region - more so than in the flatband region. 

  • 0 in reply to Michael Steffes
    Guru 140200 points

    This is good to hear Relaxed

    Kai

  • 0 in reply to Michael Steffes
    TI__Expert 3620 points

    Thanks Michael that's good to know.