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PCM4204 maximum sampling rate in DSD mode

Other Parts Discussed in Thread: PCM4204

Hi,

I am using a PCM4204 A2D converter.  The datasheet front page specifies a maximum PCM sampling rate of 216 kHz and DSD rate of 64 Fs and 128 Fs.  I am trying to determine the fastest data rate I can achieve with the device in DSD mode.  Table 1 indicates that DSD is only available in Single or Dual rate, not in Quad rate - where I want to operate.

Is it possible to use the DSD at its highest rate to capture signals up to 100 kHz, or does the Single/Dual rate filtering prevent me from operating in this frequency band?  What sampling mode and SCKI would result in the highest frequency DSD mode?

Thanks,

Jason

  • Hi Jason,

    I have asked a colleague to look into this.

    Best Regards,

    dave

  • Hi Jason,

    When in DSD mode, the output comes directly from the modulator at either 5.66 MHz in 128fs mode or 2.822 MHz in 64fs mode and does not pass through any filters. Comparing this directly to a sampling rate for PCM isn't a direct translation. So when taking the DSD output you must apply your own filter to get rid of out of band noise from the modulator, and therefore you could select a filter that would roll off near 100KHz. A nice app note that talks about this is linked here: http://www.ti.com/lit/an/slaa313/slaa313.pdf 

    Justin

  • Hi Justin,

    I agree that there is no direct comparison between PCM and PDM data formats - at least without making some basic assumptions.  The confusion is that the modulator rate is specified in relation to Fs, but what is Fs in DSD mode?  Is it 192kHz, 216kHz, 22kHz?  From your answer and Table 1, I take it that fs is assumed to be 44.1kHz.  The numbers you quoted were from the "test conditions" in the dynamic performance table and were assuming a 20 Hz to 20 kHz bandwidth.  The DSD clock can actually run higher, but I'm unclear on what the exact relationship is between the SCKI and the DSD clock rate.

    I understand that the DSD data must be reconstructed through a digital decimation filter to whatever PCM sampling rate I desire.  However, there is a filter within the modulator in the form of the noise transfer function.  This noise shaping filter will push the low-frequency noise to higher frequency bands above the designed Fs value.  In DSD mode, 64fs and 128fs are identified as single rate and dual rate in the datasheet (Table 1).  I am under the impression that Single, Dual, and Quad rate modes have different noise transfer functions that impact the high frequency (i.e. > 44.1 kHz) performance.  Please correct me if I'm wrong.

    A different way to rephrase my questions would be:

    1) What mode and clock rates should I use in DSD mode to get the best performance at the highest frequencies above 44.1 kHz?

    2) Assuming I used the exact same digital decimation filters as embedded in the PCM4204, would I expect the equivalent performance of the device running in Quad-rate PCM at 216 kHz vs. DSD at the clock rate in question 1?

    Thanks,

    Jason

  • Hi Jason,

    1. To get the best performance distortion and SNR wisse, 128fs DSD mode at fscki at 768fs is the best option but will have signal content up to 24 KHz(like running at 48 KHz in PCM). To get the most signal content, 64fs DSD with fscki = 384fs mode will be equivalent to 96 KHz and therefore you will get 48 KHz of bandwidth but with a little less performance.

    2.As with the answer above, it depends if  you are going for bandwidth or performance.

    Justin