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DAC61402EVM: DAC61402EVM

Kiran Ajjevadimath
Prodigy 120 points
Part Number: DAC61402EVM

Tool/software:

Regarding DAC61402EVM, we were trying to measure THD by providing digital codes to DAC and measure the acquired analog.

We have replicated the test conditions as mentioned in datasheet, attached screenshot for reference:

 

Test conditions:

 

Generation->

We are writing 400 codes for 1 cycle; this corresponds to 2.5us per digital code. The generated amplitude is between 1V-4V.

Using in SYNC mode.

 

Acquisition rate –> 10M sample rate.

 

 

Below is the screenshot of the acquired signal, where in we observe harmonics with respect to fundamental frequency:

 

 

 

Below are questions regarding same:

  1. The sine wave is proper, but we observe harmonics. Could you let us know how we could reduce harmonics.
  2. The THD value mentioned in datasheet is (88) but we have observed (-47), could you suggest any modifications to meet datasheet specs.
  3. We are trying to communicate with DAC61402EVM and referring to the procedure mentioned in User Guide, but the BP-DAC61402EVM folder is not present in GUI composer gallery, could you share us the required folder to communicate with Launch pad.
  • 0
    TI__Expert 4590 points

    Hi,

    We are reviewing this and will get back to you shortly.

    Thanks,
    Lucas

  • 0 in reply to Lucas Burnette
    TI__Expert 4590 points

    Hi,

    Are you using the internal reference or an external reference for these measurements?

    Also, the engineer that worked on the firmware for the project is out of office today and will be back early next week.

    Thanks,
    Lucas

  • 0 in reply to Lucas Burnette
    Prodigy 120 points

    Hi,

    Any update on the query.

    We are using Internal reference of 2.5V. 

  • 0 in reply to Kiran Ajjevadimath
    TI__Expert 5060 points

    Hi Kiran,
     
    I have sent a respond over the mail, please check and let me know if have any more questions. 

    Thanks,

    Sanjay

  • 0 in reply to Kiran Ajjevadimath
    TI__Guru 53773 points

    Hi Kiran,

    A few comments:

    1.  Improved THD numbers are dependent on a few external factors as well as device performance.  What are you using to generate the LDAC signal? Is this is a low-jitter digital source? What supply rails are you using for the DAC? Note that you could have some non-linear behavior from the DAC output if it is operating near the supply rails.

    2. Ultimately, my understanding is that the 88dB THD number is related to the 16-bit variant of the DAC.  You can calculate ideal dynamic range of a DAC using the below equation:

    Dynamic Range = 6.02n + 1.76, in dB
    n = number of bits of resolution

    Most devices do not have a better THD than dynamic range.  Using this equation we can say that the best DR for a 12-bit device is ~74db.  

    Using the 12-bit device, I would recommend that you confirm or make the following changes:

    1. Ensure your headroom/footroom is >1.25V

    2. confirm that your digital source can provide a very accurate and stable update rate for LDAC.

    3. Add low-pass filtering on the output to attenuate harmonics.