Hi,
We recently bought an eval board for the AD9911 to experiment a bit with DDS and discover how it works, but I had some trouble understanding a few things about both the evaluation software and the chip itself.
- Linear Sweep :
First is about the linear sweep. I got it working and everything, but one thing that troubled me was the need to press "P1" to apply the channel output config. Same for a linear sweep on CH0, I need to press P0 to get my linear sweep working. Does it mean that the channel output config is only applied on channel X if pin X is activated ? (Just making sure I understood correctly here)
In the linear sweep configuration window, there is a falling rate and falling step. I don't understand what these do. My guess is, the rising step is for sweeps from f1 to f2 (or phase 1 to phase 2) where f1 < f2, but I can't understand the correct config to get a falling sweep. Or maybe it's something else entierely ?
- AM Modulation :
As soon as I activate CH0 and "Test tone modulation" I can't control the amplitude of CH1 anymore, but I can control the amplitude of CH0. Is this normal ? Here's my setup :
Also, as you can see, I don't need to select "Amplitude" in the "Modulation Output Type". I'm not sure what this window is used for aside from linear sweep, and because of that I don't understand why I can set 15 different tuning words for each Channel. I tried changing values but it doesn't do anything, and I guess it's because it's used for something that needs the correct configuration but I have no idea what these 15 boxes are used for.
- Phase modulation :
I tried using phase modulation by setting up my PM CH2. I can't synchronize my oscilloscope because it's a cheap one (or maybe I can but I haven't found how to do it yet) , so my output is very unstable:
Here is my setup :
- General questions:
I had a few questions about the chip and some functionnalities that I didn't quite understand from reading the datasheet.
What is the Ramp up/Ramp Down used for ?
What are PPC bits on the software ?
Why are there 15 auxiliary channels tuning words, and what's the use for them ? I understand channel 1 being used for the end point of sweeps, but I don't understand the other ones.
I don't quite understand the "2/4/8/16-level modulation" option on the chip. I know this is mainly due to my lack of knowledge on the topic, so if you have any external source that could help me get a better feeling of these I would be very grateful.
I apologize about some of these questions that should be clear after reading the datasheet, but I've just graduated and had some trouble understanding some of the basic functions of this chip. Thank you for your help.