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TLV320ADC5140: THD and Dynamic rang relation with PGA

Ken Zhang
Intellectual 1945 points
Part Number: TLV320ADC5140

hi, all

a customer wants to know how to set PGA value to obtain better performance of both THD and dynamic range. is there any suggestion to set PGA value of TLV320ADC5140. and is there any data similar with attach?

  • 0
    TI__Mastermind 23050 points

    Hi Ken,

    The best option would be to use the DRE feature, which dynamically adjusts the gain of the PGA to achieve 120dB of dynamic range. The THD+N will not improve with PGA gain though.

    The DRE feature works by increasing the analog PGA gain at low signal levels. This gain is later removed on the digital side and leads to an overall improvement in the dynamic range because the front end PGA is designed to be lower noise than the ADC. 

    The optimal PGA gain will depend on the input level of your mic/line signal and how much noise it contributes. If you have a very low noise source then there may be a slight advantage to boosting the input with a few dB of PGA gain and removing this with the digital volume control if you do not want to use the DRE feature.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    TI__Intellectual 1945 points

    Hi Zak

    thanks for your rapidly feedback.

    "The THD+N will not improve with PGA gain though."

    Can I think the THD+ N is almost same in all PGA  gain range? if not, is there any table similar with the attach in which shows the THD+N and PGA?

  • 0 in reply to Ken Zhang
    TI__Mastermind 23050 points

    Hi Ken,

    There will be some amount of degradation actually with increasing PGA gain due to the amplification of the noise. We don't have a table for this but you can see in the spec for THD+N we give a typical value with 0dB gain and +12dB gain with other conditions the same and the difference in THD+N is ~3dB. Based on the noise vs. channel gain curve in figure 13 it is apparent that this degradation is due to the additional noise and not increased distortion.

    Best,

    Zak