ADAU1442 Clocks

Hi all,

I've got a setup in which a DSP (ADAU1442) is connected to 3 ADC (1974) as input and another DSP as output. Currently the ADAU1442 is master of the TDM stream to the ADC's bus slave to the TDM stream in the output. However, I noticed some artifacts, probably due to the internal clk difference of ADAU 1442 (XTAL) and the output. Is it possible to make the sync on the TDM signal of the output and use this same clock to connect to the ADC? Any advice on this is highly appreciated! Thanks in advice!

Best regards,

Guy

  • 0
    •  Analog Employees 
    on Nov 17, 2011 11:23 PM

    Hi Guy,

    Are you routing the output TDM stream thru the output side ASRCs? If you use the output ASRC then the ADAU1442 and the second DSP do not have to be synchronized. Also the AD1974 and ADAU1442 should have a synchronous MCLK.

    Best Rgds,

    Alan

  • Hi Alan,

    Thank you for your fast reply! I haven't been using the ASRC's because the sample rate isn't realy different, it's just the clocks that are not synced. Anyway, I can imagine that using the ASRC's could help. I will try to figure it out. If there is useful information regarding (setting up) the ASRC, please let me know, I'm not familiar with it and it looks rather complex.

    Regarding the AD1974 and ADAU1442, they both have their own crystal but the ADC is configured in slave mode. Isn't this enough? If not, is it better to use ASRC as well or make MCLK clock distribution instead of separate chrystals? Thanks in advance!

    Best regards,

    Guy

  • 0
    •  Analog Employees 
    on Nov 18, 2011 12:41 AM

    Hi Guy,

    If the master clocks are not synced then you must use the ASRCs. As for the AD1974 you must use the same master clock as the ADAU1442 with the AD1974 as slave. Otherwise you could make the AD1974 a master and use the input ASRCs of the ADAU1442. There is the option to output the ADAU1442 PLL on the CLKOUT pin that could be used to provide the MCLK to the AD1974. I think the best place to start for understanding the ASRC setup is in the datasheet (pg 58). If you have sigma studio you can also check out the graphical interface for the ASRCs and FARM.

    Best Rgds,

    Alan

  • Hi again Alan,

    Thanks again for the answer. I do have sigma studio and I was able to make the artifact go away by using the ASRC! Really impressive :-) However, I do not yet fully understand the routing because it seems that I have connected the input signal from the ADC directly to the TDM output. It's good to know that it works but I have to find how I must avoid bypassing the DSP :-) For this test, I only used 1 input and 1 output. Originally, the output signal was "dancing" (slightly shifting wrt the input signal)

    So what I did in Sigma Studio, in the "Routing Matrix" tab is this:

    I changed "Serial Output Select Pair 8" from "DSP to Serial Output Pair 0" to "ASRC Output Pair 0"

    I changed "ASRC Output Rate Select Pair 0" from "No Rate" to "Serial Output Pair 8"

    I think this is correct, so know I guess I use ASRC Output Pair 0 with the clock of Serial Output Pair 8.

    Finally, I have changed "ASRC input Select Pair 0" to "Serial Input Pair 4". Now I see the signal from the input but the DSP is bypassed. I don't know how I have to select the DSP. I'm not sure it it's important but both input as output format is TDM8.

    Best regards,

    Guy

  • Hi Alan,

    It seems that I have written a few mistakes, the input from the AD1974 are TDM4 of course :-) Regarding the outputs, I've noticed that only the 2 first channel go though the ASRC, the other channels still go through the DSP. I guess I will need the flex modes to get the 8 channels of the TDM8 output stream through the ASRC, right?

    Best regards,

    Guy