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OPA4277-SP: Noise Spectral Density Response

Jejomar Ildefonso
Expert 8590 points
Part Number: OPA4277-SP
Other Parts Discussed in Thread: OPA4277-EP, , OPA4277

Hi Team,

Our customer has noticed a discrepancy given on OPA4277-SP datasheet, particularly on Figure 3. The response were seemingly not properly aligned with the noise density given on its electrical characteristics. Apparently the proper response was similar to the Figure 3 of the OPA4277-EP datasheet. Can you help us check and verify?

Thanks in advance!


Kind Regards,

Jejomar

  • 0
    TI__Guru* 93105 points

    Hello Jejomar,

    The problem is a typo in the current noise units shown in the OPA4277-SP Section 6.5 Electrical Characteristics table. It lists the input noise current density at ƒ = 1 kHz, as 0.2 fA/√Hz. The correct units should be pA/√Hz. The correct "typical" current noise at ƒ = 1 kHz should be listed as 0.2 pA/√Hz. This would be in agreement with that shown in Figure 3 seen below, where the vertical current noise scale is fA/√Hz. Two hundred fA/√Hz is equal to 0.2 pA/√Hz.

    I will bring this table error to our Systems Engineer attention. It can be corrected on the next OPA4277-SP datasheet revision. Thanks for bringing this to our attention.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    TI__Expert 8590 points

    Hi Thomas,

    Thank you the clarifications. Another discrepancy we've noticed is the input voltage noise density at ƒ = 10Hz. The characteristics table shows a voltage noise density to be 12nV/√Hz, while Figure 3 plots this response only in the 1Hz mark. Can you check if this is another typo within the characteristics table or an error within the X-axis scaling of Figure 3?



    Kind Regards,

    Jejomar

  • 0 in reply to Jejomar Ildefonso
    TI__Guru* 93105 points

    Hello Jejomar,

    It looks like the commercial OPA4277 and Space OPA4277 datasheets have undergone some updates across the years and unfortunately some of the information listed gets a little out of sync. The input voltage noise density listed in the Electrical Characteristics table is an older 12 nV/√Hz (ƒ = 10Hz) value that wasn't updated to match the noise graph shown in Figure 3. the graph shows about 7 nV/√Hz (ƒ = 10Hz).

    The reason the Figure 3 graph is correct is that the commercial OPA4277 had an errata sheet added to its web page around 2011. It provided a newer, updated Figure 3 where the input voltage noise density was reduced based on new measurements. Both the commercial and Space versions of the product show the lower 7 nV/√Hz (ƒ = 10Hz) in their current Figure 3 graph. Here's the link to the OPA4277 errata sheet:

    The 7 nV/√Hz at ƒ = 10Hz is from the "typical" curve but it is representative of the product's noise performance.

    Regards, Thomas

    Precision Amplifiers Applications Engineering