Hello
Customer is using their own external Digital Filter and use PCM1795 as
external digital filter mode (DFTH=1).
Customer want to have questions in order to evaluate THD&SNR again
in the various ( x4 x 8 x 16 ) OS[1:0] of PCM1795 in their product.
However, to simplify the questions , Not customer's external digital filter, But
standard digital filter such DF1706, we want to know the relationship between
THD and OS[1:0}, and also SNR and OS{1:0].
Its Okay not DF1706, but you have other standard external digital filter.
condition on PCM1795
DFTH= 1
fs 44.1K/ 24bit
WDCLK= fs x 8 =352.8KHz (ex DF1706)
BCLK= 11.2896MHz
System clock= 512fs
OS{1:0] =00 or 10 (x8 x 16)
Question1
How is the difference ( in dB) of THD in case between OS=x8 and x 16 ?
Don't you have the actual data in house?
Question2
How is the difference ( in dB) of SNR in case between OS=x8 and x 16 ?
Don't you have the actual data in house?
Question3
I am sorry to essential questions like another person had same question (Appendix)
But, Please let me know the meaning about the description in PCM1795 page 45 below(*)..
Why system clock should be x 256 in case x8 (external) x 16(OS[1:0]) =128 ?
If BCLK =11.2896MHz, then system clock should be 22.5792MHz.?
I don't know the criteria about the description in the data sheet below.
My understanding of (*) is;
x8 (external) x 16(OS[1:0]) =128, and if fs were over 100KHz, then the limitation of
BCLK is 128*100KHz > 12.8MHz, then system clock should be over 256 fs ( over 25.6MHz )
>The effective oversampling rate is determined by the oversampling performed by both the
>external digital filter and the ΔΣ modulator. For example, if the external digital filter is 8×
>oversampling, and OS[1:0] = 00 is selected, then the ΔΣ modulator oversamples by 8×,
>resulting in an effective oversampling rate of 64×.
>(*)The 16× WDCK oversampling rate is not available above a 100-kHz sampling rate.
>If the oversampling rate selected is 16×WDCK, the system clock frequency must be over 256 fS.
(Appendix)
http://e2e.ti.com/support/data_converters/audio_converters/f/64/t/242041