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AD9959: How to switch between different modulation modes

Question asked by aprilaries on Feb 18, 2016
Latest reply on Mar 3, 2016 by aprilaries

Hi, I am trying to use the AD9959's modulation mode to change its frequency, amplitude and phase. I also need to switch it back and forth between the single tone mode. I am using a FPGA to drive a AD9959 evaluation board.

 

Here is how I tried to implemented it:

1. write to channel registor 0x00, select 4-bit serial mode (set [2:1] to 11)

2. carry out standard single tone operations:

  write to CFTW0 (0x04)

  write to CPOW0 (0x05)

  write to ACR   (0x06) with [12] = 1

3. write to FR1(0x01) to set modulation parameters:

  change [14:12] to the right profile pin configuration

  change [9:8]   to the right modulation level, always use straight 16-level modulation, no any other extra such as RU/RD.

4. write to the profile registers (0x0A-0x18)

5. Write to CFR (0x03) to enable modulation:

  change [23:22] to one of the three modulation modes.

6. Switch the profile pin input to modulate the signal.

7. Write to CFR (0x03) to disable modulation([23:22] = 2'b0), back to the single tone mode.

 

All the bits not mentioned are in their default values.

 

For these steps, 1, 2, 3, 4 always worked by themselves with no problem. But once I changed the modulation mode and switch the profile pin, I couldn't switch the modulation mode any more, nor turn it off.

 

For example, after some single tone operations, I followed step 3, 4, 5, 6 to modulate the signal and everything worked fine, but when came to 7, the chip didn't change mode, and it simply stuck with whatever mode I had set in step 5. I could keep modulating it, but simply can't change or stop the modulation.

 

What do I miss here? Could anyone please give some suggestion? Thank you very much!

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