ADAU1361 and 8kHz LRCLK

For F(LRCLK)=8kHz I do:

- Fpll = 49.152MHz

- R0. INFREQ [2..1]  = 11b => Fs=Fpll/1024=49152/1024=48kHz

- R17. CONVSR[2:0] = 001b => Flrclk=Fs/6=48/6=8kHz.

Bandwidth of filter for Fs=48kHz must be 48/2=24kHz – see Figure 10..18. OK?

I connect output pin ADC_SDATA with input pin DAC_SDATA.

What signal I will see at the output LOUT if on input LIN I give a signal 1Vpp with a frequency of 5 kHz (all gains is 0dB)?

Thanks

  • Hello,

    Just to clarify: You wish to have your ADC/DAC/Serial Ports running at 8kHz?

    If that is the case, then it will not be possible to use a signal of 5kHz, since it will be above Nyquist for the setup -- the maximum frequency you could use would be Fs(converter)/2.

    The settings from your post would allow for a core Fs of 48kHz, but the limiting factor would be the sample rate of the ADCs/DACs/Serial Ports. 

    Regards,

    Tyler

  • Hello, Tyler

    I would like to have signal “LRCLK” = 8 kHz.  I would like to know what will be on output of DAC if on input of ADC the signal with a frequency 4, 5, 9, 17, 25, 49 kHz.

    Data Sheet of ADAU1361 on page 1 state: “Sampling rates from 8 kHz to 96 kHz”. How can I get 8kHz? Output of PLL has to be in Fpll=[41…54]MHz (p.27). That is Fs=Fpll/1024=[40..52.7] kHz. Fs define passband of filters (Figure 10..18) – it is ~Fs/2. Frequency of output samples, it is LRCLK, goes from Fs => Flrclk=Fs/[0.5, 1, 1.5, 2, 3, 4, 6] (p.27, Figure 29.). I want to understand what does mean “Sampling rate 8 kHz” and how ADAU1361 will to work with this sampling rate and frequencies on input ADC more 4kHz.

     

    Regards,
    Alexander

  • Hi Alexander,

    The sampling rates from 8kHz to 96kHz refer to the converter sampling rates (in SigmaStudio, under the "Digital Setup" tab). This means that the ADC and DAC can operate on certain sample rates between 8kHz and 96kHz:

    The serial port will run at whatever rate is set here. So, for example, if you set the sample rate to 8kHz, then the LRCLK will be at 8kHz as well.

    Again, if you use a sample rate of 8kHz, the part will not be able to reproduce signals above 4kHz.

    Regards,

    Tyler

  • Hi, Tyler

    I asked about another: what signal will be at ouput of DAC if on input of ADC a signal with a frequency of 5 kHz, 23 kHz, 25 kHz? It for case, when Fs=Fpll/1024=49152/1024=48kHz, Flrclk=Fs/6=48/6=8kHz.

    I think that ADAU1361 can't work without good analog antialiasing filter at input if the frequency of samples (LRCLK) is lower than 40 kHz = Fpll_min/1024=41MHz/1024.
    Or I shouldn't use PLL for obtaining frequency of samples lower than 40 kHz.

    Regards,
    Alexander