We have an application that requires 16 independent bidirectional audio channels, and I'd prefer to do it with as few wires as possible.
I see that the AD1938 can handle up to 8 inputs and 16 outputs in daisy-chain mode so in theory we could do it with four of those,but I read int he data sheet they're set up as two differential stereo inputs, does that mean they can't be used independently?
I know there are other codecs with TDM, so we could potentially do it with 8 stereo codecs, but I'm not sure the topology of that and how we'd wire them up
I'm wondering the best way to go about this.
The ADCs are simply named as a stereo pair. You can use them as four mono ADCs if you like. There are a few ways that they operate as a pair but that should not cause problems for you. The mutes are separate. It is just in transmitting the data out. If you set it to I2S stereo format then the signals will go out on the I2S data as left and right channels but those are only names. So you cannot send only one channel on an I2S signal. In TDM mode you would have all four on the bus so treat them however you like.
Yes, you can daisy-chain two of these codecs to give you 8 ADC channels and 16 DAC channels. Then use another pair for the other 8 ADCs and 16 DACs.
Now I would recommend that you operate the part in TDM 8 mode. It is much more stable and easier to layout on the PCB. Then just use 8 DACs off of one codec and pair it with an AD1974 for four more ADC channels. Then it would all be TDM 8 and you will not have to run TDM lines to the second ADC. Another option is to use four of the AD1974 ADCs and one ADAU1966A for the 16 DAC channels. This is a higher parts count but it might workout better in your application from a physical layout perspective. You would not have to have the inputs and outputs close to each other. Just keep it in mind.
Thanks for the quick response!
I just want to make sure I'm understanding this correctly.
For the AD1938/AD1974 solution we'd have common LRCLK and BCLK to all four chips, then have a two pairs of data lines, data out from the codecs to the SoIC connected to the AD1938 and AD1974, and data into the AD1938 from the SoIC?
For the ADAU1966A/AD1974 solution we would have two input lines from the two pairs of AD1974, and one out to the ADAU1966A, but would we need separate BCLK and LRCLK lines for the AD1974 and the ADAU1966A? I'm guessing we would because one is transmitting 16 channels and the other is transmitting 8 in the same time?
One nice thing about our current setup is the AC'97 codecs (e.g. AD1981B) have built in analog gain controls before the ADC and after the DAC. Are there any AD codecs in the current portfolio that have similar pre-amp and post-amp features?