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DAC8554: THD performance issue for SAWtooth waveform

Tseng Roger
Intellectual 500 points
Part Number: DAC8554
Other Parts Discussed in Thread: DAC80502

Hi Sir,

I am using DAC8554 for SAWtooth waveform application, but THD cannot meet the requirements. Which DAC can I choose to have better THD performance?

Here is DAC requirements:  SPI interface, 16bits resolution at least and DAC output x2.

Regards,

Roger

  • 0
    TI__Mastermind 18546 points

    Hi,

    First of all what do you mean by THD of saw tooth not meeting requirements?  As you know, saw tooth is made up of odd number of harmonics, so invariably you will have distortion at the output, you can theoretically calculate the THD as well, i believe its SQRT(PI^2/8 -1).

    In strict terms, even though THD is applicable to any periodic signals, I rarely see anyone looking for THD of saw tooth wave.

    No coming back to your requirements, whats the max frequency of interest ?

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Intellectual 500 points

    Hi AK,

    Thank you for your quick reply. The frequency is 60Hz, the waveform as fig1.

    I must design the LPF to improve the 2nd, 3rd ...... harmonics base on our application, but LPF is not easy to cut 2nd or 3rd harmonics. However, LPF will cause the 60Hz sawtooth waveform to be poor as shown in Figure 2. My goal is to select better components to reduce the harmonics by the 60Hz SAWtooth waveform.

    Regards,

    Roger

  • 0 in reply to Tseng Roger
    TI__Mastermind 18546 points

    Hi,

    Correct me if I am wrong . If you remove 3rd harmonics completely from saw tooth, it will add distortion right? Because 3rd harmonics is the dominant factor to create a saw tooth in first place.

    Anyway since your application frequency is 60Hz, I recommend go ahead with DAC80502

    www.ti.com/.../DAC80502

    Also have a look at MDAC which is ideally suited for waveform generation applications.

    www.ti.com/.../DAC8812

    Let me know if you need more help regarding the same.

    Regards,

    AK

  • 0 in reply to Akhilesh K
    Intellectual 500 points

    Hi AK,

    Thank you so much.