• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 47 subscribers
  • Views 398 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

DAC3484EVM

Joseph Zarrabi
Prodigy 60 points

Hi. I have DAC3484EVM plugged into TSW1400. My goal is to use it as an arbirary function generator to create two pulse waveforms with amplitude of 2Volts at 1700 Hz with pulse duration of 2 us. The pulses are ON for 2 us then OFF by 588 us. Channel #1 and Channel #2 needs to be delayed from each other by 100 us. Also, I would like to create various files with different rise rise times use onboard clock (CDCE62005)?

Q1- When I am creating a .csv file, should I use 32,768 data points for one period of the pulse waveform ( 32,768 points is used for 588 us duration)

Q2- What should I put for Data Rate (SPS) for generating 1700 Hz pulses?

Q3- When I load a file from the \Test Files folder like '"single_tone_cmplx_32768_250MSP_BW_25.1MHZ.csv" for understanding how this board generate a signal, I see thast I enter 250 SPS and fft graph below shows the 25 MHz frequency. Can anyone explian to me the connection between 250SPS input and 25 MHz fft frequency? the fft frequency is always 10 time smaller than SPS input??

Q4- Do I need to modify my board to by pass the EVM board ADT4-WT balun which has a 2MHz lower bandwidth?

Q5- When I load my 32,768 data point for generating my 2 us pulses I see lots of harmonics? Is this normal?

I appreciate answers to my questions.

Thanks

Joseph

  • 0
    TI__Genius 12965 points
    Joseph,

    I will help you with your questions:
    Q1. 32768 is ok for the file length.

    Q2. The Datarate will depend on how you intend to run the DAC and the DAC interpolation modes. The Datarate is the input rate of the data to the DAC input. The DAC output rate is the datarate x the interpolation.

    Q3. The file was generated with the IF/Sample rate of 25/250. In the digital domain everything is considered as a sample and without the sample rate there is no definitive frequency, just a relative ratio to the sample rate. So you can run the pattern at 250Msps for 25M tone, or at 25Msps ro 2.5M tone. You can use the HSDC Pro tone generator to create any tone or mulitone pattern you may need. A file is not necessary for tones. However if you need a custom file ensure it follows the format of the example csv file: columns per channel, signed integer values from -32767 (-1) to 32767 (+1) for the signal amplitude.

    Q4. Yes for any periodic signal less than 1MHz you will need to remove the transformer. Refer to the data sheet for DC coupled loading and ensuring the compliance voltages are met. Typically in this case just a 50 ohm to gnd should be ok. Refer to this for more info regarding DC coupled interfaces:
    www.ti.com/.../slua647a.pdf
    Also if you may need a DC coupled Diff-SE Amp interface. If SE is ok then you can just use 1 of the outputs.

    Q5. If you are looking at the spectrum of a pulse you will see lots of harmonics of the fundamental. if you are not terminating correctly you could also be causing a lot of spurious components. Also you may just be seeing the DAC images if you did not apply some kind of anti-image filter at the DAC output. A screen shot would help with the diagnosis.

    Ken.
  • 0
    TI__Genius 9695 points
    Hi Joseph,

    I will recommend that you read this application note on data converters www.ti.com/.../slaa523a.pdf
    Regarding your questions:
    Q1,2) The number of samples you need to generate will depend on the sampling frequency you select. I will suggest sampling rate >5MHz so that you can sample the 2us pulse. After selecting the sampling frequency and generating the pulse, you can enter this frequency value into HSDCPRO.
    Q3) You should rather enter '250M' into HSDCPRO and not '250' to display the FFT at the correct frequency
    Q4)Yes, you will need to take the output from the DAC before it goes to the balun. Note that the DAC has a differential output so you will lose 6dB of power if you take the signal from either the positive or negative output
    Q5)Yes, this is normal. You will not see harmonics only if you generated a pure sinusoid. Since you are generating a pulse, the harmonics are expected.

    Thanks,
    Eben.