We are using ADAU1452 chips and evaluation board for our designs and prototypes. ADAU1452 evaluation board comes with AD1938 audio codec which can support up to 8 analog outputs. ADAU1452 DSP on the other hand can support up to 48 digital output channels via serial 4 serial ports using TDM.
My question is that what is the best method to extend analog outputs up to 12 channels? Is it possible to use multiple AD1938 codecs and connect each chip with serial port lines (SDATA_OUT, BCLK_OUT, LRCLK_OUT) of the DSP? Can we use multiple EVAL-AD1938 evaluation boards along with EVAL-ADAU1452 to prototype this?
Any feedback in this regard will be very helpful for our design needs.
I would look at the ADAU1962A. It is a 12 channel DAC. You could get a 1938 eval board. A second board would add 8 more channels giving you 16 total. But the issue is with the configuration of the ADAU1452 eval board. If you have the newer EVAL-ADAU1452REVBZ board then you can modify it for control from the DSP or from SigmaStudio. The problem with the original board is that you can only run operate the codec in standalone mode and for that part it is only I2S at 48kHz fs. The part is capable of up to TDM 16 and 192kHz fs but not in standalone mode. So you would need to buy two AD1938 eval boards to get 12 channels. So this is why I suggest using the 1962.
The ADAU1962A has several options to run in TDM mode while in Standalone operation. Although, for development it is good to operate the part from SigmaStudio so you have real-time control of register settings. Eventually you can setup the DSP to boot up the codecs.
Many thanks for the prompt response and providing this excellent feedback for our design.
Using ADAU1962A seems like best option to go forward with. We are not married to any particular DSP or audio codec at this time, so we are flexible in choosing parts that fit our design. We have extensively used 1452 and 1466 DSP here.
From your response, I understand that interfacing ADAU1962A DAC with ADAU1452 DSP will provide 12 analog channels. We can prototype this by connecting DSP evaluation board and ADAU1962A eval board together. Connections can be made by tapping the serial test points on the DSP board that are situated between the DSP and DAC ICs. (Option 2 in the image). Each serial link will comprise of SDATA_OUT, BCLK_OUT, and LRCLK_OUT.
Alternate design, would be to use two AD1938 boards and routing 2 serial channels to one board and another 2 serial channels to the second board to get a total of 16 analog outputs. Option 1 below - less preferable.
Does this look right to you?
Many thanks for your feedback and help in this.
PS. ADAU1452 Eval board that we have is labelled version# V1.0 130802 (ADAU142MINIZ)
We also have several ADAU1466Z DSP evals with us and we can get new ones if you suggest a different board/DSP.
I think option 2 is the simplest and lower cost for you. We also have the ADAU1966A which is a 16 channel DAC. The eval board looks the same and both parts function the same.
When it comes to hooking it up. You are correct that you tap off of the test points for the LRCLK, BCLK and the SDATA. The codec on the DSP eval board will still be connected but will not cause issues.
Since you have to run signal fairly far, I would either use two TDM-8 lines or four TDM-4 lines if possible. This keeps the frequency down and avoids issues with jumping the signals over between boards. Running TDM-16 would most likely give you some issues and flakiness with the digital transmission. I notice this in our lab all the time, if I run at TDM-16 I have to place the wires into a position where they work and then don't touch them. Even bringing my hand close can sometimes cause issues. Even still, I can usually hear a stray click every once in a while.
To help minimize this I suggest you use a ribbon cable for the interconnect. Then on the odd wires, 1,3,5,... you connect those all to ground on the DSP board. (you will have to probably twist them all together and tie them to one of the ground test points.
Then on the even pins you use those for signals, master clock, bit clock , LRCLK, and the SDATA pins. This way each pin has a ground wire running along with it to keep the impedance defined and provide a return path for parasitic currents. On the DAC eval board, I designed in a ground pin for each header so for instance, the external LRCLK header pins, J3, pin 1 is ground and pin 2 is the signal. Tie the ground wire on the ribbon cable that runs alongside the LRCLK to the ground pin of J3. You can do this for each signal and that should help your transmission of the digital data. I am using buffers/level translators so pay attention to the direction.
Regarding the eval board, either one would work.