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AD9208 Recommended for New Designs
The AD9208 is a dual, 14-bit, 3 GSPS analog-to-digital converter (ADC). The device has an on-chip buffer and a sample-and- hold circuit designed for low...
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AD9208 on Analog.com

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AD9208: Harmonic of Decimated FS mixes with NCO



		

			

									
					    Dwijen.Pandya
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 19, 2017 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    
 
    I am using AD9208 for one of my application. I am using AD9208-3000EBZ+ADS7-V2EBZ for the evaluation
    
 
    In my setup Fs is 3GHz
    
 
    Decimation Rate is 8
    
 
    Decimated Fout (Decimated Fs) is 375MHz (3GHz/8)
    
 
    NCO is 702MHz
    
 
    RF In to the ADC is 800MHz
    
 
    I have observed that there is spur in the output spectrum that is arising from mixing of the harmonic of Fout with NCO.
    
 
    For the above setup there is spur at 48MHz.
    
 
    2*375MHz - 702MHz = 48MHz
    
 
    The snapshot of the ACE setup and the output spectrum is attached.
    
 
    Is this spur expected? What can be done to minimize this spur?
    
 
    Regards,
    
 
    Dwijen
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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                on Dec 23, 2017 2:33 AM
            
            
					
        
	
        

		
		
        
					
        HI Umesh,
        
 
        Thanks for reply, Your always prompt response is really amazing and I appreciate same. 
        
 
        I didn't quite understand following statement.
        
 
        "What you see at 48MHz/3GSPS and 45.75MHz/2.991GSPS is the DC spur that has been rotated, and filtered".
        
 
        Would you be able to provide some explanation on this DC spur rotation mechanism?
        
 
        Regards,
        
 
        Dwijen
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Dec 23, 2017 2:33 AM
            
            
					
          
	
          

		
		
          
					
          HI Umesh,
          
 
          Thanks for reply, Your always prompt response is really amazing and I appreciate same. 
          
 
          I didn't quite understand following statement.
          
 
          "What you see at 48MHz/3GSPS and 45.75MHz/2.991GSPS is the DC spur that has been rotated, and filtered".
          
 
          Would you be able to provide some explanation on this DC spur rotation mechanism?
          
 
          Regards,
          
 
          Dwijen
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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