• State Resolved
  • Locked Locked
  • Replies 1 reply
  • Subscribers 30 subscribers
  • Views 253 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PCM1864-Q1: Question about antialiasing filter

Lee, Sam
Expert 5585 points
Part Number: PCM1864-Q1

Hi team,

  

Would you please answer the following question?

  

Regarding Antialiasing filter, the datasheet recommends 100ohm/0.01uF for single-ended and 47ohm/0.01uF for differential. This is about fc=160kHz. When considering audio bandwidth 20 ~ 20kHz, the fc=160kHz looks high. If fc is lowered, the SNR expected to be better, isn’t it? Can you explain why you set it higher?

  

Thanks,

Sam Lee

  • +1
    TI__Mastermind 37040 points

    Hi Sam,

    The ADCs are delta-sigma ADCs, meaning it's going to oversample and decimate out-of-audio-band noise anyway. If you observe the test circuit, it doesn't make use of any RC filtering either.  I'm not sure exactly why that cutoff was chosen, but I would keep the resistor value close to the same in order to match with the input impedance of the device. You could change the capacitor if you desire a lower cutoff.

    But I would only use the filter if you have significant out of band noise, in the 100s of kHz to MHz region. Typically the device can meet spec without the additional RC filter.

    Best regards,
    Jeff McPherson