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INA137: Higher THD+N @ 10kHz in Recent Lots

Bob Bauman
Prodigy 60 points
Part Number: INA137

For parts with date code 61QH1 and 61EG4, we observed THD+N @ 10kHz  that is higher than previous lots from the past 15 years. All of the 1201 parts used from a 2.5K reel of date code 61QH1 had to be replaced. 

Previously our measured THD+N with a 10kHz / 19dBu sine wave input was -108dB to -110dB. For the same measurement, this lot shows a value of -104dB typically.

The load on the output is 3.46k ohms.
The output signal level is 13dBu / 3.46VRMS

Replacing the part with one from an older date code resolved the distortion issue.

We observed the same reading from parts that were placed by our contract manufacturer and hand-soldered in-house.

NOTE: I submitted this to the TI Customer Support Center with a Customer Information Form, but they directed me to this site. I can send this form.

  • 0
    TI__Guru 60610 points

    Bob,

    The INA137 THD+Noise specification at f=10kHz has TYPICAL value of 0.0005% (106dB - see below) BUT its magnitude may vary due to normal process variation.  The variation in the distortion is primarly caused by the change in the sheet resistance (+/-15%) values as well as variation in the bandwidth of the part (+/-30%).

  • 0 in reply to Marek Lis
    Prodigy 60 points

    Hello Marek,

    Thanks for the reply.

    I understand that we are measuring THD+N levels close to that shown in the graph. However, it seems that something must have changed in the fabrication of these parts. They have been very consistent for 12 years, but the most recent batches are showing this issue.

    Was there a fabrication change?

    Has anyone else reported this?

    Have counterfeit versions of these parts hit the market?

    Regards,

    Bob Bauman

  • 0 in reply to Bob Bauman
    TI__Guru 60610 points
    Bob,

    It looks like your suspicion regarding possible INA137 process change might be justified. A year or two ago, there was a process change that effected EPI doping levels, which may affect THD+Noise performance. By now, the issue has been corrected but the question is if the wafer lots in question were also affected. I have asked process team to cross-reference the date codes you sent me (61QH1 and 61EG4) but until now, I have not received a definite answer. Thus until I hear from them it may be safe to assume that in fact the cause of the lower THD+Noise you measure is caused by the process change.
  • 0 in reply to Marek Lis
    Prodigy 60 points

    Marek,

    Thanks for the update. Please let me know what you find. 

    We have parts that we would like to return if justified.

    Bob

  • 0 in reply to Bob Bauman
    TI__Guru 60610 points

    Bob,

    This issue aligns timewise with a noise problem found at our fab. This has since been resolved but material that was fabricated in this time period is susceptible to THD+Noise issue. However, the engineer I am working with told me the lot trace code (LTC) you provided is incomplete.  If we can get the full LTC, we can pin point the exact fabrication date and based on the assembly date we can extract from the LTC, we will be able to conclusively determine whether the wafer lots in question were effected.

  • 0 in reply to Marek Lis
    Prodigy 60 points

    Hi Marek,

    Here's a picture of the label on the reel with the 61QH1 parts.

    Bob

  • 0 in reply to Bob Bauman
    TI__Guru 60610 points

    Bob,

    The process engineer has confirmed that the lot in question was produced AFTER the process change was implemented, which means that the temporary issue we had with the process does not explain your problem and therefore, the fix will NOT eliminate a possibility of the "issue" to show in the future lots.

    Having said that, you wrote before: 

    “Previously our measured THD+N with a 10kHz / 19dBu sine wave input was -108dB to -110dB. For the same measurement, this lot shows a value of -104dB typically.”

    So you actually used to see THD+Noise at 10kHz slightly better by few dB's than datasheet curve below shows (0.0005% ~ -106dB)  and now you see it 2dB lower. As I said before, these are typical specs that may somewhat vary over process variation.  But seeing that your issue occurs at 10kHz, which is right at the inflection point of the THD+Noise curve, any variation in load or bandwidth (may vary up to +/-30%) could easily produce such effect. 

  • 0 in reply to Marek Lis
    Prodigy 60 points

    Understood, but I am disappointed that we have to loosen our testing spec after so many years. I wish they still worked as consistently as they did. Oh well.

  • 0 in reply to Bob Bauman
    TI__Guru 60610 points
    Agree. I wish we could prevent the process from variations but this is simply not possible especially when the fab is moved between locations.