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Is ADC TDM8 possible using AD1938 and ADAU1978?

Hello all,

I have a question about ADC TDM mode.

There are 8 analog inputs coming in.

8 ADCs are needed.

They have to be able to transfer data in TDM8.

I would like to ask you if my idea is possible or not.

Could you look at the attached file "ADAU1978 Figure32.PNG"

There are 2 slave ADCs in the image.

The top one is ADAU1978.

The bottom one says ADAU1978 or "Similar ADC".

Can this similar ADC be alternated with AD1938 codec's ADC part? 

(AD1938's pin no. 20, 21, and 22 are ASDATA1, ABCLK, ALRCLK)

Back ground of this question

8ch ADC(TDM8 has to be possible) and 4ch or 6ch DAC are needed in the system.

If my idea above is not possible, I guess there are 2 ways to accomplish the system with ADI products.(see below)

Alternative idea No.1

Using 2 of AD1938 so that there are 8ch ADC and 16ch DAC

Also on the ADC side, TDM is possible by Daisy-Chain mode in the data sheet p.19

Alternative idea No.2

Using 2 of ADAU1978 so that TDM8 is possible in the way of Figure 32 (serial port connection option 5) on p.20

However, AD1934 DAC is needed for the DAC requirement.

In summery, 

Both Alternative idea No.1 and 2 has drawback.

In alternative idea No1, 16ch of DAC are too much for the system.

In alternative idea No2, using 3 ICs would cause higher BOM cost.

So, could you tell me if it is possible to output data from ADAU1978 and AD1938 in the TDM8?

Best Regards,

Yuta Mihara 

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  • Hello,

    I would recommend using your alternative idea #1. The reason your main idea would be less-than-satisfactory is that ADAU1978 does not have any DACs, so you would need to add in an additional chip for the DACs.

    However, if you have some flexibility in what chip you use for your DSP, you could consider using an ADAU1701 with two ADAU1978s. This would give you 8 ADCs, 4 DACs, and processing capabilities. You could also use the ADAU1701 as a way to bridge two TDM4 outputs from the ADAU1978s into a single TDM8 stream.

    Regards,

    Tyler

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  • Hello,

    I would recommend using your alternative idea #1. The reason your main idea would be less-than-satisfactory is that ADAU1978 does not have any DACs, so you would need to add in an additional chip for the DACs.

    However, if you have some flexibility in what chip you use for your DSP, you could consider using an ADAU1701 with two ADAU1978s. This would give you 8 ADCs, 4 DACs, and processing capabilities. You could also use the ADAU1701 as a way to bridge two TDM4 outputs from the ADAU1978s into a single TDM8 stream.

    Regards,

    Tyler

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