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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 22, 2017 12:18 AM
            
            
					
        
	
        

		
		
        
					
        Hi Dwijen,
        
 
        What does the full BW plot look like with the filter in line?
        
 
        Also, what does the DDC spectrum look like when you remove the input signal (turn RF Off)?
        
 
        I am afraid I dont fully understand the 48MHz = 3*375MHz - 700MHz math. Are you implying that this 425MHz tone aliases to 50MHz? I am also curious as to how you came to the 3*375MHz conclusion.
        
 
        If you check the FFT spectrum, the 48MHz is tagged as "DC Frequency" in ACE. I am not sure if this is correct. Would it be possible for you to
        
 
        - take an FFT (with DDCs on) with the 5% BPF between the MXG and analog input
        
 
        - export the raw data and send it to me
        
 
        Thanks
        
 
        Umesh
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Dec 22, 2017 12:18 AM
            
            
					
          
	
          

		
		
          
					
          Hi Dwijen,
          
 
          What does the full BW plot look like with the filter in line?
          
 
          Also, what does the DDC spectrum look like when you remove the input signal (turn RF Off)?
          
 
          I am afraid I dont fully understand the 48MHz = 3*375MHz - 700MHz math. Are you implying that this 425MHz tone aliases to 50MHz? I am also curious as to how you came to the 3*375MHz conclusion.
          
 
          If you check the FFT spectrum, the 48MHz is tagged as "DC Frequency" in ACE. I am not sure if this is correct. Would it be possible for you to
          
 
          - take an FFT (with DDCs on) with the 5% BPF between the MXG and analog input
          
 
          - export the raw data and send it to me
          
 
          Thanks
          
 
          Umesh
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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