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PCM4222: THD+N questions at 48Khz and 96Khz sample rate

Kailyn Chen
Genius 9560 points
Part Number: PCM4222

Hello,

About the THD+N, I have a question to interrupt you.

The dynamic range is about 121dB, that is to say the ADC quantized noise is about-121dbfs. But when the sample rate is 48Khz and 96Khz, the THD+N are both 108dB under the conditions at  both input amplitude  -1dbfs, I don't understand about this.  Because the bandwidth is 22~40Khz at 96Khz sample rate, the integral bandwidth is twice of 48Khz sample rate. why did the THD+N get worse? 

Best regards

Kailyn 

  • 0
    TI__Genius 13610 points

    Hello Kailyn,

    A larger bandwidth does not mean it will have better THD+N at lower frequencies and oversampling does not always improve THD+N performance substantially. What ever causes this discrepancy will probably be hard to find since it is a older part, but it is most likely just a byproduct of this specific chip's design when it steps up from 48KHZ to 96KHZ there is some additional circuitry that is activated and may be causing some more noise to occur, so you are fundamentally correct that it should be but you always should consider-variations that occur from other unrelated noise especially when the input frequency is far below needing to oversample.

    Best Regards,

    Carson

    Low Power Audio Applications