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About ADAU1979 signal quality

there had a Interference signal approaching 5K

the adau1979 reg cfg in next ( TDM8 + 48K + 12.288MKZ + LRCLK MODE):

addr: 0x0 data : 0x1
addr: 0x1 data : 0xd1
addr: 0x2 data : 0x4a
addr: 0x3 data : 0x7d
addr: 0x4 data : 0x3f
addr: 0x5 data : 0x5a
addr: 0x6 data : 0x0
addr: 0x7 data : 0x10
addr: 0x8 data : 0x32
addr: 0x9 data : 0xf0
addr: 0xa data : 0xa0
addr: 0xb data : 0xa0
addr: 0xc data : 0xa0
addr: 0xd data : 0xa0
addr: 0xe data : 0x2
addr: 0xf data : 0xff
addr: 0x10 data : 0xf
addr: 0x11 data : 0x0
addr: 0x12 data : 0x0
addr: 0x13 data : 0x0
addr: 0x14 data : 0x0
addr: 0x15 data : 0x20
addr: 0x16 data : 0x0
addr: 0x17 data : 0x0
addr: 0x18 data : 0x27
addr: 0x19 data : 0x0
addr: 0x1a data : 0x0

Is it caused by hardware?

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  • Hello hebing,

    How are you measuring this? The units are cutoff in your screenshot but it looks like Vrms? So therefore you are going through a DAC and other circuitry?

    The spike is at a curious frequency in that it is not a harmonic of 1kHz. 

    What is the input level to the ADC? At the pins. 

    If you look at figure 6 and 7 in the datasheet, you will see what is expected of the part. This was measured directly digitally. Figure 6 is with a lower level signal and figure 7 is with a -1dBFS signal which is just before clipping. You will see the resulting distortion products are all harmonics of the 1kHz fundamental. 

    So I suspect it is something else in your system that is involved here. 

    I do not think this will be a clock jitter issue but I cannot rule that out. 

    I would look at power and ground carefully. Is there anything in your system that might produce a 4.5kHz signal? LED controllers? 

    Change the input frequency and see if it changes with it?

    Try a level that is about -20dB from full scale. 

    Dave T

  • Hello Dave:

    I‘m very gland for your reply!I had found the reason,the power of ADC not reach expect 8V

    tksy very much.