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dac3162

serkan unal
Prodigy 160 points
Other Parts Discussed in Thread: DAC3162, DAC3152EVM

we try to produce a 10 MHz sin wave with a sampling frequency 80 MHz, we generate that sin wave with 8 sample points. the analog output of DAC3162 seems as stepped as in the attachment, i think we should make an interpolation filter, does this behavior of the dac is normal, can you check our schematics also. dac is controlled over a fpga, we are sure about the digital data we gave to dac.

regards,

  • 0
    TI__Guru* 91947 points

    Serkan,

    What is the DAC driving, a transformer? Can you send the output section of your design? How does the output look if you use 16 or more sample points?

    Regards,

    Jim

  • 0 in reply to jim s
    Prodigy 160 points

    dac is driving an opamp as below, and that opamp is driving a demodulator in another board. we did not try 16 sample points exactly but signal seems good below 2 mhz with 80 mhz sampling frequency.

  • 0
    TI__Guru* 91947 points

    Serkan,

    I ran a test with a DAC3152EVM and a TSW1400EVM. The fewest data points I could use with the tone generator is 32. I created a 10M sinewave and captured the results with the DAC sampling at 80MHz. The output was very close to what you are getting. With this DAC, you cannot get a better waveform unless you provide more sampling points, speed up the sample rate, or slow down the IF.

    Jim  

  • 0 in reply to jim s
    TI__Genius 12965 points

    Sekan,

    The DAC ouput looks correct although you do need to implement an anti-imaging filter. 

    The DAC output in this case for 10MHz using 80Msps will take 8 samples per cycle.  The reason you are seeing the steps is due to the sample and hold nature of the DAC output .  If you look at the signal with a spectrum analyzer at a span larger than 3-4x Fs, you will see the DAC images at mutiple of Fs.  If you want a clean sinewave you will need to put in a low pass filter to remove the images.  Once the images are removed you will get a clean /smooth 10M tone.  In this case a 20-30M LPF would be adequate

    Ken.

  • 0 in reply to Ken C
    Prodigy 160 points

    It be very late to response, sorry for that, LPF filter works, waveform and spectrum seems better with it. Thank you very much.

    regards,

    serkan