AD9102 Triangle wave with 78,125 KHz

Question

Trying to generate a Triangle wave with 78,125 KHz, 156,25 KHz, 312,5 KHz, 625 KHz, 1250 KHz, but I could not find any thing about the frequency for Triangle or Sawtooth wave. 
 I use the example2_4096_ramp.txt and example4.regval file, then I have changed: 
 the WAVE_SEL1 0x027[5:4] to 1 
 the SAW_STEP1 0x037[7:2] to 4. 
 So I have no idea how to change the frequency. 
 
 Actually, for the sin wave, I could easily change the frequency, by changing the DDS frequency in the DAC1 tab. 
 but for the Triangle wave, is vague. 
 Thank you in advance.

ADIApproved · Accepted Answer

Hello, 
 Unfortunately the triangular waveform won't fit your need. The triangular waveform always ramp from positive full scale toward negative full scale and back in 1lsb step. To do what you want, you need to take multiple lsb steps. I suggest you use the on-chip RAM to store your waveform instead. 
 Regards, 
 Will)

akbar · Answer

Hello Will, 
 thank u so much for the reply. 
 below lsb 1 step:

and this one, lsb 3 step: 
 
 1- Is that what u mentioned ? 
 As u mentioned, I used SRAM, to load my waveform (1 lsb and 3 lsb) and as Regval File, I use example1.regval to have triangular waveform. 
 2- How can I have Continuos triangle waveform ? 
 2.1- in this case, should I use the example6.regval ? (Actually, for the sin wave, I used the example6.regval and could easily change the frequency, by changing the DDS frequency in the DAC1 tab.) 
 3- Still I do not konw how to change the frequency !!! 
 
 Best regards, 
 Akbar

ADIApproved · Answer

Hello Akbar, 
 Sorry for the delayed response! I was in a conference the last few days. 
 1. Right. But you can't have 3lsb step in the triangular waveform function, you can with SRAM. 
 2. You set PATTERN_RPT (reg0x1F[0]) to 0, and PATTERN_PERIOD (reg0x29) to the number of samples in the triangulare wave period. 
 3.You can either store multiple waveforms and change the start and stop address as you change frequency; or you can load a different waveform. 
 Regards, 
 Will

akbar · Answer

Hello again Will, 
 and thank u again for the reply. 
 I guess almost I did the same!! 
 Yes, the PATTERN_RPT (reg0x1F[0]) to '0', is clear, as it is mentioned in the data sheet, but regarding the 'PATTERN_PERIOD (reg0x29)', I thought when I choose to read from the SRAM (WAVE_SEL 0x0027[2:0] to '0'), I can not change the 'PATTERN_PERIOD (reg0x29)' anymore. But suddenly I varried the value to the number of samples in the SRAM, so there was useful, and then, I set the 'START_DLY 0x005C[15:0]' to '0'. 
 Regarding the 3rd answer, 
 I loaded different waveforms. 
 
 At the end, your answer was absolutely useful. There are enough post, about the same question in the forum, but they're not actually useful for me. at least, I could not find such a answer like yours.

Fullscreen 
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-2016
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-1984
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-1936
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-1872
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-640
-624
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-576
-560
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-528
-512
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-464
-448
-432
-416
-400
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-368
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-336
-320
-304
-288
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-256
-240
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-144
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ADIApproved · Answer

Hello Akbar, 
 4. By changing offset do you want to center it around VDD/2? Unfortunately you can't not do that without a external amplifier or transformer. The output is DAC current from VDD to VSS, thus the minimum output is VSS (when that current is zero). 
 5. The 12bit RAM data is signed, so it goes from -2048 to +2047. 
 Regards, 
 Will

ADIApproved · Answer

Forgot to mention that for 4. you could also do AC coupling or resistive level shifting etc. In either case you need some kind of hardware modification.

ADIApproved · Answer

Hello Akbar, 
 Adding a digital offset shifts one output up and the other down. You will need to reduce your swing to avoid clipping the waveform. 
 Regards, 
 Will

ADIApproved · Answer

Dear Akbar, 
 Unfortunately there is no such option, otherwise it would be ideal for your application. But you can store up to 4096 samples, so you can store multiple waveforms, and change the start and stop address (and pattern period) as you change frequency. 
 Regards, 
 Will

akbar · Answer

Hello Will, 
 concerning the 4- offset, not only VDD/2, but maybe lower or even higher. 
 
 Does the DAC Digital Offset Register (DACDOF, Address 0x25) the same ? 
 
 Regards, 
 Akbar

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AD9102 Triangle wave with 78,125 KHz