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PCM1821: PCM1821 Input gain scaling factor for Mic and Line input not clear through datasheet

Ravindra Desai
Prodigy 250 points
Part Number: PCM1821
Other Parts Discussed in Thread: PCM1861, PCM1822, PCM1820, PCM1860

Hello,

I want to use PCM1821 (no dynamic gain enhancer feature) as a SLAVE in my designs sometimes as ADC with line input and sometimes as ADC with analog Mic input.

My question is:

Normally there is a PGA to set the gain for the ADC input channel to enable user to use it as a line or mic input.

PCM1821 does not have any such provision. So how does PCM1821, in SLAVE mode, set the scaling factor for line/mic input?

Is there be fixed gain value for Mic input and another for line input that the device will use depending on the input signal level or is there something like a single straight line curve that both mic and line inputs will use? Can I use one channel for mic and another for line input input on the same chip?

Thanks in advance!

  • +1
    TI__Mastermind 32845 points

    Hello Ravindra,

    Thank you for reaching out. As you have noticed, the PCM1821 does not support the Dynamic Range Enhancer (DRE). The DRE monitors the incoming signal amplitude and accordingly adjusts the internal DRE amplifier gain automatically (see sections 8.3.6 and 8.3.7 of the datasheet for more information). Without this feature, the ADC will read the value at the input (with no gain) whether it is mic or line level. If an integrated amp is needed for your application, then please note that PCM1820 and PCM1822 are pin compatible and will have the DRE feature. Otherwise, there more TI audio ADC's that have a PGA if that is needed (such as the PCM1860 or PCM1861).

    I hope this helps. Let me know if you have further questions.

    Best,
    Andrew