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TLV320AIC3204: TLV320AIC3204 spur detected on harmonic bands

Leo Chow
Expert 3120 points
Part Number: TLV320AIC3204

Hi,

I'm in midst of working with end customer on evaluation of TLV320AIC3204EVM and we encountered emission or spur at around 405.5MHz and 417.7875MHz which is coming from TLV320AIC3204 CODEC when we set the codec as master (generating BCLK=6.144MHz and FS=32kHz) from MCLK of 12.288MHz. We have separate analog and digital ground design & implementation recommendation. The 405.5MHz and 417.7875MHz are harmonics of 6.144MHz.

To root cause the issue further, we tried to perform RF sniffing on AIC3204 EVM board using spectrum analyzer and found that even before CODEC programming there is already a 405.5MHz spur. Do you have any idea where is the spur coming from? I still haven’t provide any MCLK to the CODEC. 

Regards,

Leo

  • 0
    TI__Mastermind 30210 points
    Hi Leo,

    The EVM spur is likely related to the MCLK you are providing. 6.144Mhz would be a likely AOSR and DOSR. but if you didn't even program the Codec, then it has nothing to do with the codec, the clock dividers are powered down, the PLL is powered down, ADC and DAC powered down. nothing is happening.

    If you had the EVM board plugged into the USBMODEVM, then there is a TAS1020B usb audio processor on board.

    best regards,
    -Steve Wilson
  • 0 in reply to Steve-Wilson
    TI__Expert 3120 points
    Hi Steve,
    as per your comment above you're suspecting i'm getting the spur readings from my MCLK? yes i'm also ruling out potential variables such as register settings, PLL, clock power up/down states since i'm was able to capture 405.5MHz even before codec setting kicks in. AOSR & DOSR were just registers for ADC & DAC oversampling registers hence i don't think it may cause this.

    Regards,
    Leo
  • 0 in reply to Leo Chow
    TI__Mastermind 30210 points

    Leo,  

    are you measuring this spur on the output of the DAC?  or are you measuring EMI emmisions?

    There will be out of band noise on the output of the Codec.  if you want that to dissappear, use a passive LPF.

    see the application note: Out-of-Band Noise Measurements in Audio Codecs

    best regards,

    -Steve Wilson