AD9959 channel output signal amplitude and phase

Hi sekou ,

Let me take a look at this and see what I can do. I have to consult my colleagues if they have other ways to have these channels in phase. 

All the best,

Jules

Hi Jules.Nikko ,

Ok waiting for your answer.

Updates!

Right now i'm playing with the evaluation software and I see that the signals tends to be more in phases with increased frequency in the order of the 100 KHz, while at 25 KHz i had the same results with the driver I implemented, I am more than confused I was expecting to see all the channel outputs in phase no matter the frequency in the evaluation software. I'm keeping it with my investigation. For more information, here is a screenshots of the output signals both with the evaluation software and with my drivers. I also included the setup I used with the evaluation software, with a clock of 25Mhz since I used an external crystal clock to control the chip manually.

The Channels output Amplitude and phase difference between channels with the Evaluation Software

The Channels output Amplitude and phase difference between channels with my C driver

As you can see the results are quite similar but I was expecting to have all the channel output in phase in both cases.

Thanks again

Updates!

I've been doing a lot of testing and it seems that the higher I go with the frequency, the more the signals tends to be in phase, I believe that is because, the frequency range in the datasheet is on the order of 1MHz to 500MHz. But what if I require signals in the order of 0KHz to 50Khz, is it doable with this board ? Or if it requires hardware modification, which one would be required ? I'm thinking about replacing my 25MHz crystal clock with a 25Khz one even though I know the datasheet specify using one between 20 and 30 MHz .Also, I believed the mas amplitude is from the range of AVDD+- 0.5V so between 1.3V and 2.3V (if that's the case, I would like confirmation) but as you can see  I'm in the order of mV is there a reason why ?

thanks again

Hi sekou ,

I was able to ask around my colleagues who have done AD9959 synchronization in the past and what you are experiencing, as the four channels are not exactly in phase, that is valid and is normal. You still have to set some phase offset to get your desired output frequency in phase. Apologies but the minimum REFCLK frequency is 1MHz. Just to clarify, for you to achieve the output of 25kHz, you have to make use of the higher REFCLK which is the 500MHz. The minimum frequency you could generate is 0.6Hz, 

All the best,

Jules

Ok got it! What about the fact that I don't see the same amplitude at 25KHz, should If I use 20 as a clock multiplier to achieve 500MHz as a REFCLK will it be better ? End by saying that the minimum REFCLK frequency is 1MHz, you are talking about the external crystal clock I can use ? If I set some phase offset to get the frequency output in phase the thing is that, I realize that I might need to apply it every time there is a change of frequency so could it be better to use a PLL after the output to do the trick ? And lastly what is the best frequency range of operation of the board?

For now, i'll try to set the multiplier on 20 and see the results. I will keep you posted on this discussion on it.

Thanks for the reply

I am experiencing weird things trying to set the clock multiplier to 20 in order to have 500MHz as a REFCLK, I did set up the right bits in the FR1 register (bit 22 and 20 set to 1 and bit 18,19 and 21 to 0) but now I get half of the frequency output I desire, I tried to fix it by dividing by 10 the frequency tuning word I get after doing the calculation we find in page 18 of the datasheet, it seemed to work but after some time, every frequency output are divided by 10. Why does this occur ? Either way I can have something at 5Khz but only 2 out of the 4 channel outputs a good looking signal, I give a screenshot as example below:

Channel 0 and channel 1, 5Khz frequency output:

Channel 2 and channel 3, 5KHz frequency output:

The more I go down in frequency, the more the output on channel 0 and channel 1 tends to be deformed. I'll keep looking on it.

Is there a board 4 channel board like the AD9959 that works well between 25KHz to 50KHz with both output frequencies in phases all the time, I am starting to consider that I might not have the best hardware for what I intend to do with my project

Hi sekou ,

Sorry for getting back to you for a long time. I'm going through all my emails and unanswered thread just now and might have missed your updates. 

On our DDS Product Selection Guide, only AD9959 has 4 channel output. You might also want to consider looking at AD9106. I'm not an expert with the product but I saw it also has 4 outputs. 

Also, I'll attached a PDF here just for your guide on selection.

. PDF

All the best,

Jules