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LME49723: THD+N vs AMPLITUDE for LME49723

yoshiki hasebe
Mastermind 6385 points
Part Number: LME49723

Dear Sirs,

My customer asked us about THD+N vs AMPLITUDE for LME49723.

He measured and compared THD + N vs AMPLITUDE with LME49723 and other devices in the same circuit currently in use.
The result is shown below.


So LME49723 is getting worse at the green circle in this figure.

Please let me know the possible cause of this THD deterioration.

Best Regards,

Y.Hasebe

  • 0
    TI__Guru* 84915 points
    Hasebe-san,

    The LME49723 THD+N is measured under certain conditions to get the correct results. It is important to consider that the THD+N behavior may vary depending of these factors or conditions.

    I recommend to try with different loads to check the differences in the THD+N. The driver is made for 600ohms preferentially, but you may try also with loads of few Kohms. Ensure that the AP is using an A-weighted and the signal is filtered from 22Hz to 22KHz. If possible, add a measurement filter to reduce out-of-band noise. We recommend to use a passive 1st order low-pass filter with 1Kohm and 4.7nF.

    This will generate the best results for the device.

    Please let me know how your measurements result.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Mastermind 6385 points
    Hello Luis-san,

    Thank you for your reply.
    I will explain your suggested trying methods to my customer.

    I will reply the result to you if i have measurement result from my customer.

    Best Regards,
    Y.Hasebe
  • 0 in reply to yoshiki hasebe
    Mastermind 6385 points

    Hello Luis-san,

    I heard to my customer.

    He uses the following circuit configuration.
    The current output from the DAC is I / V converted by the LME49723 circuit.
    The output is a differential output that uses a configuration that outputs through the second stage op amp via a coupling capacitor.
    The block configuration is as follows.

    Then he measured at two loads.
    NG at 2 kΩ (1 kΩ / ch)
    THD deterioration from about 7 Vrms or more
    It was OK with 3 kΩ (1.5 kΩ / ch).

    If you need more details, please let me know your email address.

    Best Regards,

    Y.Hasebe

  • 0 in reply to yoshiki hasebe
    Mastermind 6385 points

    Hello Luis-san,

    I checked datasheet of LME49723.

    Then, I found figure 8 as follows.

    Looking at this yellow circle,
    It looks like it is getting worse rapidly from around 8 Vrms like my customer's figure.

    Do you think this is the same? Or is it different?

    Please let me know about them.

    Best Regards,

    Y.Hasebe

  • 0 in reply to yoshiki hasebe
    TI__Guru* 84915 points
    Hasebe-san,

    Thank you for pointing on this. This definitely is similar to the customer issue. As you may see in the figure, this issue appears at the same THD+N value. So, it seems that it is related to the LME49723 normal behavior.

    Best regards,
    Luis Fernando Rodríguez S.
  • 0 in reply to Luis Fernando Rodriguez S.
    Mastermind 6385 points

    Hello Luis-san,

    Thank you for your reply.

    I understand your comments.

    I will explain them to my customer.

    Best Regards,

    Y.Hasebe