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THS4521 as microphone pre amp

ASB
Intellectual 355 points
Other Parts Discussed in Thread: PCM1804, THS4521, OPA836

Hello,

I would like to use THS4521 as pre-amp for  my design for better noise figure.  The microphone signal is 2.5mV single ended input a low impedance source. The output of THS4521 will be connected to PCM1804 ADC.  Is THS4521 is a good choice for pre-amp application? 

  • 0
    TI__Genius 13935 points

    Hello,

    You may want to consider a two stage configuration.  If you want to drive the ADC to near full scale that is 60dB of gain which is a lot of gain for a single stage amplifier.  It might be best to use a single ended op amp for the first gain stage and then use an amplifier like the THS4521 for the single ended to differential conversion and the final gain. 

    It might be best to post a question on the audio forum for the best first stage amplifier selection.  Once you have the first stage designed we can help with the single ended to differential and the final gain into the ADC.  I would think you don't want much more than 30dB of gain in the differential amplifier.  Usually you want the most gain in the first stage to set the noise floor. 

    Regards,

    Loren

  • 0 in reply to Loren Siebert 1
    TI__Genius 12631 points
    Hello,
    In addition to Lorens comments, you want the closed loop BW of your amplifier to be at least 100x the audio frequency band to ensure there is minimal signal degradation. So that is 20KHz * 100 = 2MHz. You now want a gain of 1000 to use the full dynamic range of the ADC. You can look for a gain of 50 in stage 1 and 20 in stage 2. I would recommend using the OPA836 for your 1st amplifier stage and the THS4521 for your 2nd amplifier stage. There is a delicate balance here between how much gain you can put in the front end to minimize noise and how much signal degradation you are going to see. Do you have an estimate on the THD+N requirements of the system at say 1KHz?
    -Samir