Distorted CW Output Waveform

Hi tvil ,

Just wanted to as if you are using a custom board or the evaluation board? Can you by any chance share what your setup looks like? 

All the best,

Jules

Hi Jules

I'm using a custom board.

I read the following values back from some of the registers via SPI, if it helps:

CSR: 0x000000F6

FR1: 0x00000000

FR2: 0x00000000

CFR: 0x00000314

CFTW0: 0x37DAC37E

CPOW0: 0x00000000

ACR: 0x000013FF

LSRR: 0x00000101

RDW: 0x0001BE9E

FDW: 0x0001BE9E

CW1: 0x37DAC2BD

(Some of the modulation-related registers have non-zero values since I want to implement FMCW later. But for now I just want to get a clean single tone - as you can see modulation is disabled via CFR[23:22])

Some relevant portions from the schematic:

All of the control signals goes to a FPGA.

(There are 3 DDS devices on the board.)

Filters on output of DDSs after the transformer.

Thanks

I found cause of my problem - we were driving the amplifier at the filter input (PSA-8A+) strongly into compression which distorted the signal. If we reduce the DDS output amplitude the signal looks much better.

My next problem - I still can't seem to control the output amplitude while frequency modulation is active - as explained in this old post of mine:

 https://ez.analog.com/dds/f/q-a/564852/ad9959-constant-amplitude-multiplier 

Regards

TV