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Low AD9912 Output Amplitude

Question asked by sean.donnellan on Sep 18, 2015
Latest reply on Sep 21, 2015 by mcee



I have had a prototype board made containing an AD9912 chip with a ADT2-1T transformer to convert the DAC output from differential to single-ended (50 ohm). I have not used external termination resistors on the differential side


On start-up with {S1,S2,S3,S4} = {1,1,0,1} and a direct 1GHz clock I see a 61.4 MHz output as expected. However the amplitude is only ~-18 dBm. I then have an amplification stage and see a clean ~0 dBm signal.


Does anyone have any ideas why the voltage might be so low out of the DDS? One difference from the Analog Devices evaluation board is I am not feeding the DAC output back into the DDS chip (as I am not using any of the HSTL or CMOS outputs from the DDS).


Digital pins I am controlling (currently constant):


PWRDOWN         Low

RESET                 Low

IO_UPDATE         Low

CSB                     High

SDIO                    Low

SCLK                   Low


I have not set any other registers.