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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 21, 2017 3:59 PM
            
            
					
        
	
        

		
		
        
					
        HI Umesh,
        
 
        Thanks for reply.
        
 
        Yes I am using MXG for
        
 
        MXG1 -> Generate 800MHz ADC input tone
        
 
        MXG2 -> Generate 3GHz ADC Fs
        
 
        MXG3 -> Generate Ref Clk  (375MHz for Full BW mode)
        
 
        There are no filters between MXG and ADC input.
        
 
        The Full BW Mode spectrum is given below as  you requested.
        
 
        
 
        I have also tried putting 5% BW sharp cutoff BPF on the signal input. Input Sig Freq and BPF center freq is 800MHz.
        
 
        I still see the spur at 48MHz. The ACE setup is same as that shared before.
        
 
        48MHz = 3*375MHz - 700MHz
        
 
        
 
        The BPF response is similar to that shown below. The below response is at 1GHz.
        
 
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

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                on Dec 21, 2017 3:59 PM
            
            
					
          
	
          

		
		
          
					
          HI Umesh,
          
 
          Thanks for reply.
          
 
          Yes I am using MXG for
          
 
          MXG1 -> Generate 800MHz ADC input tone
          
 
          MXG2 -> Generate 3GHz ADC Fs
          
 
          MXG3 -> Generate Ref Clk  (375MHz for Full BW mode)
          
 
          There are no filters between MXG and ADC input.
          
 
          The Full BW Mode spectrum is given below as  you requested.
          
 
          
 
          I have also tried putting 5% BW sharp cutoff BPF on the signal input. Input Sig Freq and BPF center freq is 800MHz.
          
 
          I still see the spur at 48MHz. The ACE setup is same as that shared before.
          
 
          48MHz = 3*375MHz - 700MHz
          
 
          
 
          The BPF response is similar to that shown below. The below response is at 1GHz.
          
 
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

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