ADAU 1772 and SSM3525 digital inputs

Hi,

I am trying to get back the current of the SSM3525 into the ADAU1772 with PDM communication.

I am using both eval boards to do that and I saw that the DMIC0/1 Data are wired together.

Then, I am able to read both current and voltage when the data comes out from the SSM3525.

But now, I am trying to put a digital microphone on DMIC0 and to read the current on DMIC1. Then, I am not able to get the microphone signal with the eval board of the ADAU1772 because the signal from the SSM3525 is short-circuiting the microphone signal but is there a possibility to separate the data from DMIC0 and DMIC1 (If I am routing my own PCB) to get both signals ?

I can not use input2/3 because I am already using the ADC to input another signals...

Thanks in advance for your help.

  • 0
    •  Analog Employees 
    on May 4, 2020 7:45 PM 3 months ago

    Hello YBecher,

    I think there is a little bit of confusion of these different formats. What you are asking to do is possible but not quite in the way you are trying to do it. 

    The I/V signals from the SSM3525 are a TDM format which is a format that holds multiple channels of audio in PCM format. PDM digital microphones use PDM formatted single bit stream audio which is a very different format to PCM.  They certainly are not compatible together. 

    So what you need to do is bring in one mic using the PDM inputs to the decimator. You will lose the ability of using ADC0 and 1 but that seems like it is OK with what you described. So the microphone will come in on the PDM inputs. 

    The SDATAO outputs of the SSM3525 need to be wired up to the Serial input port 0. So the I/V signals will be on those channels. There are options for how the part formats the data but that is another discussion. 

    Then you can route the one channel from the microphone into channel 0 of the DSP and one channel of the serial data input to the channel 1 of the DSP and both will be available in the core. 

    You select these options on the routing page of the register controls in SigmaStudio.

    Dave T

  • +1
    •  Analog Employees 
    on May 8, 2020 3:01 PM 2 months ago

    YBecher,

    I want to clear some things up: the SSM3525 can send I/V sense data in either PDM or TDM/I2S format. 

    In PDM format, the I_SENSE data will be the left channel and V_SENSE data will be the right channel.  There is less configurability in PDM Mode, so unlike TDM/I2S mode we are unable to change the location of the Sense data or to disable certain bits from being driven.  Because of this, the project you have described would not work as currently setup. 

    The PDM I/V sense data from 3525 will need to have a set of 2x DMIC channels dedicated to it, either DMIC0/1 or DMIC2/3. 

    It should also be noted the ADAU1787 may be a better option for this type of project, as it can accommodate 8x DMIC channels along with the 4x analog inputs. 

    Please let us know if there are more questions. 

    Thanks,

    PG

  • Thanks for the reply PG,

    Unfortunately, that was the answer that I was expecting... It seems that the ADAU1772 will not do the job for our application. I can not drive neither I2s/TDm nor PDM to combine every inputs that I need. I will check if I can maybe use I2S digital microphones or something else which should be compatible with the communicaiton of the 3525.