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How to connect array mic using PCM1864

Muraki.k
Prodigy 30 points
Other Parts Discussed in Thread: PCM1864, PCM1862

Dear TI-san.

I have two question(or requirement) about PCM1864.

It will attach a document that will provide detailed information.

Quetion1:

Our use condtion as follows.

・Analog input 4-ch(single-ended mic input for array-mic), External analog input 2-ch(L/Rch).

　In 4-ch array-mic, We need sampling at the same timing (LRCLK same Edge).

・Audio output I2s I/F using TDM-mode.

In our use condtions, Could you tell us the recommended about these input connections to pcm1864 analog inputs?

Please see the attached file for details.

Question2:

About Serial Audio Interface Timing

In datasheet(SLASE55A, page50), Figure45, there is describe audio data format by timing chart.

We would like to know also about TDM-mode. Could you provide us the data format of TDM-mode?

 

Best regards,

Muraki Kazuo.

  • 0 in reply to Muraki.k
    TI__Mastermind 27850 points
    Hi Muraki,

    1. For arranging the inputs, you have given valid examples of use cases in the attachment. There are two muxs, Left and Right, which talk to 2 ADCs each. Therefore if you want to use all 4 ADCs, 2 inputs must be on the L inputs, and 2 must be on the R inputs. As for the external input, either option you presented could work, but it might be a little less confusing if you went with option A since left will be a L input and right with be a R input. The reason either will work is because of the mixers shown in figure 38 of the PCM1864 data sheet. This shows that any of the ADC outputs (CH1L, CH2L, CH1R, CH2R) can be mixed to either output.

    2. When working in TDM mode you must have BCK at 256*Fs, and we suggest using 48 kHz sampling or 96 kHz sampling. Single pulse mode can be used in slave mode, but an LRCK with 50% duty cycle must be used in Master mode. Resolutions available are 16-bit, 20-bit, 24-bit, and 32-bit. 32-bit has 8 bits of padding for each word while the rest have no padding.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 30 points

    Dear Justion-san

    Thank you for your comment.

    I'm sorry, the condition of our use case was not enough.
    Analog inputs of 6ch, array-mic(4ch-single ended) and external(2ch -R/Lch),
    we use all of them at the same time.
    I have attached the updated information.

    In this case, use the four ADC(CH1L, CH2L, CH1R, CH2R), is it possible sampling the inputs of 6ch?

    About your TDM explanation, could you show us the timing chart, like image of Figure45(Audio Data Format).

    Best regards,

    Muraki Kazuo.pcm1864_qa_revb.pdf

  • 0 in reply to Muraki.k
    TI__Mastermind 27850 points
    Hi Murakai-san,

    Using one PCM1864, you will only be able to sample 4 channels at the same time, in order to do 6 channels you would have to add another PCM186X part. If 6 is your target you could add a PCM1862 or 3, as well as another 4 channel part such as the PCM1864.

    The secondary ADC is meant to sample either DC levels for things like volume control from a pot, or when in sleep mode to identify a signal on an input while using less power. While you can output the secondary ADC info in TDM mode it is only a singla channel, and it is the output after the LPF or after the HPF.

    To sample 6 channels at the same time 2 PCM186X parts will need to be used. These parts would then be able to transmit all 6 channels on the same I2S line using TDM mode. If you set one part to transmit 4 channels of data, it will leave the data line in Hi-Z so that another device on the bus can drive it. For the second PCM186X part you would set the offset of the TDM transmit to be 4 channels of data, the PCM186X would then leave the data pin HI-Z until the desired offset, then drive the line with it's 2 channels of data.

    Justin