• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 1 answer
  • Subscribers 31 subscribers
  • Views 847 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLV320AICXXXX codec advertised sampling rates

Manjula Ellepola
Expert 1335 points
Other Parts Discussed in Thread: PCM3070, ADS1271

Hi

I am looking for a suitable audio codec with high enough sampling rate. In the above series I find that there are two main versions of the chips, one with 96kHz and the other series with 192kHz sampling rate. This is advertised on the website as well as the starting page of the data sheet. However digging further into the data sheet only discusses setting sampling rates of 48kHz and lower. No where does it say how to set 96kHz or a non standard sampling rate.

Is the advertised maximum sampling rate there to pull in people but cannot really be set or used even if settable?

Please clarify.

Thanks

Manjula

  • 0
    TI__Guru 62006 points

    If the configuration for a certain sampling rate isn't specifically shown in the datasheet or user's guide, the chapter about the clock configuration will have information how to set up the part.

    For example: AIC3254, Application Reference Guide http://www.ti.com/lit/an/slaa408a/slaa408a.pdf, chapter 2.7, table 2-25:

    Desired sampling rate = 192kHz.

    Max. x_MOD_CLK = 6.756MHz --> max OSR = 6.756/0.192 = 35.1875 --> closest OSR as a power of 2 is 32.

    x_MOD_CLK = 192kHz * 32 = 6.144MHz.

    If you use a standard audio master clock of 24.576MHz, you can omit the PLL and just use the dividers N = 1, M = 4, OSR = 32 and the ADC or DAC will run at 192kHz sampling rate.

     

  • 0 in reply to Dominik Hartl11
    Prodigy 50 points
    TI datasheets relating to TLV320AICxxxx series make me want to pull my hair out sometimes, at least the PCM3070 datasheet doesn't seem quite as seriously lacking (although does suffer some similar ambiguity etc) - pity my boss is making me use TLV....
  • 0 in reply to Robert Thompson26
    Expert 1335 points

    Hi Robert

    I agree with you. TI needs to seriously look at the way they structure the data sheet and also provide enough information. I spend hours trying to decipher and extrapolate what a chip can really do. This is highly important before committing to a design and product down the track.

    Regards

    Manjula

  • 0 in reply to Dominik Hartl11
    Expert 1335 points
    Hi D.Hartl

    Thank you for the reply and information. You are correct above. I managed to set the TMS320AIC3106 to 96kHz sampling rate and confirmed that the output frequencies are as they should be.
    I still have a couple of questions?
    1. The output from the DA has got a lot of high frequency noise at the higher sampling rate. I am thinking this is from the lower order sigma delta used at higher frequencies. Am I correct? This would mean that there needs to be added filtering that needs to be done before feeding into a PA.
    2. The DS does not state the resolution of the a/d or d/a. It just says that the converted data can be op in 8/16/24 and 32 bit. So what is the actual resolution of the convertors? Does the resolution get set when we choose a particular data width?
    3. There are no specifications for anything above 20kHz. I understand that this is the audio b/w. However if the chip can be used at higher sampling frequencies one would expect some specifications. Are we on our own when we want to use a higher bw than 20kHz..
    4. Am I better of using a stand alone sigma delta A/D if for example I need 36kHz bw?
    My application is ultrasonic and these AIC chips have got attractive features such as AGC on them.
    I await your valued advice.

    Regards

    Manjula
  • 0 in reply to Manjula Ellepola
    TI__Guru 62006 points
    1: OSR is only 32 so there will be more noise due to less oversampling. You will have to use an analog LP filter that gets rid of frequencies above 48kHz. This is especially important if your PA is a switching amp otherwise you'll get aliasing.
    2: The d/s for an audio converter typically specifies SNR+D instead. You can calculate the effective number of bits of resolution ENOB = (SNR+D - 1.76) / 6.02. The data width doesn't affect the SNR+D except if it is less than the ENOB.
    3: That's because it is an audio converter. If you need factory data for frequencies outside the audio band there are other, more expensive products like the ADS1271: www.ti.com/.../ads1271
    4: If you need guaranteed performance and don't mind the higher price, a precision converter (like the ADS1271) may be a better choice. If you are satisfied with the expected performance of an AIC, it could save you money.