AD9739

Question

Dear Sir/Madam,

Currently 
 , 
 
 I 
 
 do 
 an 
 experiment 
 
 with multi-chip 
 high-speed 
 
 DAC 
 AD9739 
 , 
 
 but 
 
 when 
 measuring the 
 
 DAC 
 output 
 
 signal 
 , 
 I 
 found 
 
 highr 
 
 harmonics 
 . 
 
 Experimental 
 
 procedure 
 
 is as follows 
 : 
 
 using 
 
 single 
 
 frequency 
 
 sine 
 -wave 
 data 
 
 of 
 
 DSP output to FPGA, 
 through 
 
 FPGA the 
 data returns back 
 
 to 
 the 
 DAC 
 chip 
 
 AD9739 
 and 
 
 use

Spectrum 
 
 Analyzer 
 to 
 measure 
 the 
 output 
 
 sine wave 
 
 signals 
 
 SFDR 
 . 
 
 In 
 the 
 spectrum 
 of the 
 output 
 
 signal 
 , 
 
 single 
 
 frequency 
 
 sine 
 
 signal's 
 
 harmonic 
 
 power is larger 
 , 
 
 resulting 
 in 
 poor 
 SFDR 
 output 
 
 signal 
 
 of 
 
 DAC 
 , 
 
 the actual 
 wave figure 
 please see 
 
 attached 
 
 pictures 
 . 
 
 Hardware 
 : 
 
 signal 
 
 source 
 
 si 
 clock 
 
 chip 
 
 ADCLK914 
 clock 
 . 
 O 
 utput 
 
 analog 
 
 front end 
 of DAC is referring 
 
 to 
 use 
 
 methods 
 
 recommended 
 
 in 
 the 
 manual 
 , 
 
 differential 
 
 output 
 
 signals connenct 
 
 90 
 
 Ohm 
 
 resistor 
 
 to 
 
 ground respectively 
 , 
 
 and then through 
 
 transformer 
 transfering 
 differential 
 
 signal to 
 
 single 
 
 ended 
 
 signals 
 , 
 
 AC coupled 
 , and then 
 
 plus 
 
 low 
 - 
 pass 
 
 filter 
 to 
 get 
 
 a 
 
 1GHz 
 output 
 
 signal 
 .

I 
 do not 
 
 know 
 
 how 
 to promote 
 harmonic 
 
 power 
 
 to 
 
 improve 
 
 SFDR 
 ?

Could you pleas help clarify above.

Thanks.

danf · Accepted Answer

Poor harmonic performance is often caused by poor balance of the clock input and/or the DAC output. Can you check the baluns that you are using, the PCB trace lengths, and ensure that you have good balance on both?