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AD9739 Production
The AD9739 is a 14-bit, 2.5 GSPS high performance RF digital-to-analog converter (DAC) capable of synthesizing wideband signals from dc up to 3.0 GHz....
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AD9739 on Analog.com

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When the ad9739 outputs a DC voltage, the low-frequency noise will change with the DC voltage.

		
	
				

			

									
					    applo168
					
							


			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on May 19, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
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                The user observed that the AD9739's low-frequency noise increases with the DC output voltage. The final answer explains that this is expected due to the AM noise from the master bias generator, which modulates the DAC's full-scale current. The noise is most noticeable at full-scale outputs due to the lack of common-mode rejection. The accompanying answer suggests measuring before the FDA in the schematic for further insight.
                        	    
    
                
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    Category: Hardware
    
    		        		            		    
    Product Number:  AD9739  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi：
    

    When the ad9739 outputs a DC voltage, the low-frequency noise will change with the DC voltage. 
    

    As shown in the figure below：（The voltage output value has the following three situations： DC = 0V，DC = 0.2V, DC = 0.45V ，The output voltage noise will increase as the output voltage value increases。）
    

     
    

    AD9739 output termination circuit (DC Coupling) is shown in the figure below：
    

     
    

    Is this result consistent with the AD9739 specification? What may be the cause? Thank you
    
			
    
			
									
		                             
                        

    
    
                                            
                 Standard High Speed D/A Converters
                
                                                    
                 hardware
                
                                                    
                 High Speed D/A Converters =30MSPS
                
                                                    
                 ad9739
                
                                                    
                 vlotage noise
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on May 21, 2025 8:30 PM
            
            
						
			            		
      
		
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      Hi  ,
      

      Thank you for your interest in AD9739. We'll check this and get back to you as soon as possible. Just a question, have you tried measuring before the FDA in your schematic? 
      

      Best regards,
      Marco
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Jun 17, 2025 9:46 AM
            
            
						
			            		
        
		
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        Hello,

        This observation is to be expected since the DAC's low frequency noise is dominated by the master bias generator for the weighted current source array that is central to the DAC architecture.   Note this noise is AM in nature since it is modulating the DAC's full-scale current as compared to PM noise that is due to jitter on the clock signal.   When the DAC code is at mid-scale..........the current is equally divided between the IOUT outputs hence one gets the benefit of common-mode cancellation by an interface circuit (i.e. balun/transformer or diff-to-single-ended amplifier) that has decent common-mode rejection.  When the DAC is cost is at + or - full-scale , all of the DAC's output current is directed to one or the other IOUT outputs hence no rejection of this AM  noise source
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
						
						
				
				
		
		
        
			
		
        
	
        

        

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