• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 30 subscribers
  • Views 272 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.

Original question:

PCM1808 integrated antialiasing LPF

PCM1808-Q1: Antialiasing filter characteristics

Yoshikazu Kawasaki
Expert 3510 points
Part Number: PCM1808-Q1
Other Parts Discussed in Thread: PCM1808

Hello,

My questions are related to the post shown below which asked for antialiasing filter.

1) The antialiasing filter cut off frequency is shown on page 4 as -3dB at 1.3MHz when it is Fs=48kHz, but is it the same for other frequencies?  For example, will it be like 430kHz at Fs=16kHz?

2) Is it possible to provide the frequency response curve?  My customer would like to know if it is -12dB/oct, -18dB/oct or others.

3) Would you please tell me the reason why it is set to -3dB at 1.3MHz?  My customer would like to design external peripheral circuit for noise reduction by the information.

/t/559956?tisearch=e2e-sitesearch&keymatch=PCM1808

Best Regards,

Yoshikazu Kawasaki

  • 0
    TI__Mastermind 23050 points

    Hi Kawasaki-san,

    This is a simple RC filter inside the device and it should be a standard -20dB/decade rolloff after the -3dB cutoff and it should not scale with sample rate.

    I don't have an easy way to show a frequency response curve since this also largely gets filtered out by the modulator and there is no way to probe the modulator inputs directly to see just the effect of the anti-aliasing filter.

    I don't know why 1.3MHz specifically was chosen but this is sufficiently high to avoid any impact to the audio band and filter out high frequency noise that may couple to the input pins.

    Best,

    Zak