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Original question:

PCM4202: Vcom pin bypass cap

PCM4202: Low frequency noise

Mochi
Genius 4035 points
Part Number: PCM4202
Other Parts Discussed in Thread: , OPA1632

Hello,

Our customer had proceeded to build ES unit and measured noise floor of PCM4202.

Then low frequency 20Hz noise floor level is 15dB higher from 1KHz.

And also Vcom noise characteristics has almost same low frequency noise.

It seems ADC output noise floor got strong influence from Vcom noise.

 

They want to verify this characteristics on PCM4202EVM but we can not find EVM here.

Could you duplicate it on your site.

I will forward you our customer captured noise floor data to your private mail box later on.

Regards,

Mochizuki

  • 0
    Genius 4035 points

    Hello,

    Here is additional information from the customer.

    Their input buffer stage is not OPA1632 type differential amp but normal OPAs are used for non-inviting and inverting stage biased by VCOM.

    That is why VCOM noise is not canceled.

    Can we take a workaround that filtering VCOM noise by RC filter from VCOM pin to OPAs? Do you see any concern?

     

    Regards,

    Mochizuki

  • 0 in reply to Mochi
    TI__Mastermind 23050 points

    Hi Mochizuki,

    It's always recommended to have at least 0.1uF bypass capacitance on VCOM. Are you sure they are not testing with the HPF of PCM4202 disabled? Are they measuring VCOM noise at the VCOM output, or at the output of their amplifier? It may also be possible that the amplifier is contributing significant 1/f noise.

    Best,

    Zak

  • 0 in reply to Zak Kaye
    Genius 4035 points

    Hi Zak,

    Thank you for your comments and e-mail communication.

    Now we got customer's understandings.

    Regards

    Mochizuki