I wanted to generate a sequence of (frequency) chirps, say LFM, meanwhile precisely control (set) the phase values, say piecewise step, for each frequency chirp? Can I use DDS to realize this? Which chip should I use?
DDS is probably the best choice for this, you will specifically want to choose one that features an auxiliary (sweep) accumulator and a Phase Offset register. When you say you want to control the phase values, if you mean the phase at which the chirp starts, that's simple with the Phase Offset Register. If you mean the phase value at each step in the sweep, you might also want to look at something with RAM capability.
Thanks for the reply! Yes, we need to add a phase offset at the beginning of each chirp. Could you suggest an ADI chip number for this task?
Many of our devices have both phase offset and sweep capability. If you look at the IST for the DDS portfolio, and filter for only those that have a sweep accumulator, you will see the full list. Each of those devices has Phase Offset capability as well.
Thanks for the reply again. If we do need to change the phase value for at each step of a frequency chirp, could we use DDS to achieve this? You mentioned "look at something with RAM capability"; could you provide more details on this?
Devices which have RAM on them generally allow you to sweep through the RAM field, and you can program different phase/frequency settings for each step. You'd be limited by the depth of the RAM, I haven't had anyone ask about doing this before - it will require some work to implement. You'll need to calculate the stream of frequency and phase words you'll need at each step..
Can you recommend any devices from ADI which have RAM on them?
AD9910 and AD9954 are the two that jump to mind
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