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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: 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 27, 2017 12:08 AM
            
            
					
        
	
        

		
		
        
					
        Hi Umesh,
        
 
        Thanks a lot for the explanation.
        
 
        I have observed that,
        
 
        In the snap shot you sent from your lab on Dec 22 has this spur present. However the amplitude you observe is lower than what we are observing. I have reattached the snapshot in below.
        
 
        The amplitude of the 48MHz spur in the below snapshot is -98dBFS. The amplitude we are observing is around -94dBFS.
        
 
        I have also observed that this spur amplitude is changing almost dB by dB with clock amplitude.
        
 
        I have set clock power to be 10dBm on the MXG sig gen.
        
 
        What clock power was used for the below snapshot in your lab?
        
 
        Also is there a spec on the clock phase noise for AD9208?
        
 
        
 
        Regards,
        
 
        Dwijen
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Dec 27, 2017 12:08 AM
            
            
					
          
	
          

		
		
          
					
          Hi Umesh,
          
 
          Thanks a lot for the explanation.
          
 
          I have observed that,
          
 
          In the snap shot you sent from your lab on Dec 22 has this spur present. However the amplitude you observe is lower than what we are observing. I have reattached the snapshot in below.
          
 
          The amplitude of the 48MHz spur in the below snapshot is -98dBFS. The amplitude we are observing is around -94dBFS.
          
 
          I have also observed that this spur amplitude is changing almost dB by dB with clock amplitude.
          
 
          I have set clock power to be 10dBm on the MXG sig gen.
          
 
          What clock power was used for the below snapshot in your lab?
          
 
          Also is there a spec on the clock phase noise for AD9208?
          
 
          
 
          Regards,
          
 
          Dwijen
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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