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AD1974 8-Channel AUX ADC Mode

Question asked by Chrill on Jul 24, 2012
Latest reply on Jul 25, 2012 by Chrill



I plan to use the AD1974 in TDM mode (so 4 data slots followed by 4 empty tdm slots). The ALRCLK signal is generated by an external clock generator and ABCLK is generated by the AD1974s PLL. Now it turned out that I also need to squeeze some kind of timestamp (which is also produced by the external clock generator module) inside the data channel. I figured that it would be quite neat to use one of the unused TDM slots to carry the timestamp. I think that using the 8-Channel AUX ADC Mode as depicted in Figure 7 in the AD1974 datasheet could do the trick, however, I'm not sure about the relations between ALRCLK, AUXLRCLK and AUXBCLK as well as the required data format of AUXDATA1.


Say I use a sampling frequency of 48kHz. Using 8-Channel TDM ALRCLK would have to be 384kHz (this I generate externally). ABCLK generated by the PLL is then 12.288MHz (32 bit wide slots).


- What would AUXLRCLK and AUXBCLK be in this case?  

- What is the data format for AUXDATA (32 bit / 24 bit)

- Is the idea of using the fifth TDM slot for the timestamp feasible at all?

- And: What exactly is the difference between TDM and AUX mode?