DIR9001 and PCM1702

Percy,

For the DIR9001, it can handle sample frequencies at a minimum of 28kHz and max of 108kHz.  The jitter frequency it can handle should be 0.25UI for most ranges of frequency.  For the PCM1702, the oversampling ratio should depend on the digital filter used preceding it, Figure 4 gives an example of this in the d/s. 

Hi Patrick,

thanks for your reply. For the DIR9001 I was asking more about the jitter attenuation capability (governed by the pll loop bandwidth) of the device rather than jitter tolerance, unless you are saying there is none, meaning the outgoing clock follows the incoming stream very strictly and all jitter on the incoming stream thus gets transferred to the outgoing clock ?

Typically a "loose" pll will buffer the jitter but a "tight" pll will track the input edge for edge. How much looseness in the pll there is, if any, is what I am inquiring about.

Thanks.

Hi Percy, I built similar DAC without oversampling, but with PCM1704 chips. They are very similar to PCM1702 but with 24 bits instead of 20. For interfacing to DIR9001 you must build some glue logic, which buffer 32 bit data for left channel and delay data for 11 clock cycles to line up with Latch (LE) signal. This converts I2S data format to format useful for this DAC. With DIR9001 it works for me perfectly up to 96kHz/24bit and with CS8416 also up to 192kHz/24bit. Complete build manual is available on my page: http://www.pavouk.org/hw/modulardac/en_pcm1704.html There is also S/PDIF decoder board with DIR9001 chip.

Hi Pavel,

thanks for your reply. Whether its PCM1702 or 1704 what I am still trying to find is how do you disable oversampling in the dac ?

Hi Percy,

Both PCM1702 and PCM1704 are R-2R types DACs. They haven't OVERSAMPLING. You don't need to disable anything. Oversampling is made by EXTERNAL oversampling digital filter like DF1704. Example for 44.1kHz CD: BCK will be 2.8224Mhz, LE (LRCK, WCK) will be 44.1kHz. DATA are in line with BCK. Oversampling filter multiply these frequencies. For example 8X oversampling filter will send BCK and data with frequency 22.5792MHz and LE 352.8kHz. It is for 64bit long frame (32bit per channel). If you want PCM1702 WITHOUT oversampling, you need only glue-logic, which converts I2S signal to separated data for two single-channel DACs and align LSB bit with WCK signal. You can get I2S from S/PDIF decoder DIR9001, CS8416 or similar or from USB receiver like PCM2706. I have one here: http://www.pavouk.org/hw/modulardac/en_pcm2706i2s.html

Ok thanks. I guess these ambiguos statements in the datasheets confused me -

PCM1702 - 'CAPABLE OF 16X OVERSAMPLING'. and 'The PCM1702 also features a very low noise (120dB typ SNR: A-weighted method) and fast settling current output (200ns typ, 1.2mA step) which is capable of 16X oversampling rates'

PCM1704 - '8X OVERSAMPLING AT 96kHz'

They could have just said it supports upto xxxKhz sampling rate. Why bring oversampling in the picture specifically ??

It is possible that authors of datasheet expected that DAC will be used always in oversampling mode. NOS DACs are not much popular today at general public. DAC with oversampling looks much better on the paper. R-2R DAC is also much expensive for manufacturing. Today we can see, that DAC producers goes a little back to the NOS DACs with "fast-roll off" characteristics of digital filter or jitter reduction. For me is the best sound from NOS DAC specially PCM1704. I am not happy, that this DAC is marked like NRND and TI doesn't have another R-2R DAC replacement. PCM1704 is now best non-oversampling DAC ever. There exists information about new 24bit NOS DAC AT1401 with balanced output, but it is probably not manufactured yet. http://www.ardatech.com/1401.shtml I want to see something similar from TI.

Or TI might just buy them up :) like they did Burr Brown.

Thanks for posting abotu the DAC I wasn't aware of it. I can see all the diyers and audiophiles drooling...