Edwar Baihaqi

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8 years, 7 months ago.

how to change the DDS AD9850 phase?

hello everyone,

i am currently working with MBED LPC1768 and DDS AD9850 from Analog Device. i use the code from Liam Goudge to control the DDS

https://developer.mbed.org/users/liamg/code/AD9850-function-generator-SPI-driver/

in his code, he explained that he left the phase as 0 degree. but, when i was trying to change the phase into 90 degree, i found nothing's changed when i saw the result in oscilloscope.

is there anyone have any idea to resolve this problem?

thank you for you attention

1 Answer

Miloje Zecevic
8 years, 7 months ago.

Hi Edwar,

How do you observe the signal on the oscilloscope? Is this the only signal on screen that you observe (no reference one to compare to)? If so, then it is hard to see on oscilloscope single phase shift when you reprogram the DDS to change the phase. Things you could do: - write mbed program that sets initial frequency of output signal to lets say 1MHz. - in main loop:

  • set phase = 0 deg
  • wait 2 sec
  • set phase = 180 deg (to ensure biggest phase jump)

If you set the time base on your oscilloscope so you can see 3 or 4 signal periods, then every 2 seconds you should see signal shift to left (and right) as the phase changes - this looks like signal jumping horizontally on screen. Trigger level should be on the middle of Vpp. Of course, all above is worth only if your mbed programs DDS correctly. Let us know the result.

Cheers, Miloje

Accepted Answer

hi Mr Zecevic,

first, i want to thank for your answer,

yes, i only observed that signal on oscilloscope. like you said, i found that was hard to see the difference between 0 degree signal and 90 degree signal. i will try what you have been suggested to me, thank you very much Mr. Zecevic

Best Regards, Edwar

posted by Edwar Baihaqi 06 Oct 2015