Products In This Thread

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...
Datasheet
AD9208 on Analog.com

  • Replies 16 replies
  • Subscribers 40 subscribers
  • Views 4022 views
  • Users 0 members are here
Options
Related 

        

            Post
             Go back to editing
        

    

    


    

    




















	
	
			
	
		
		
	
	
		

		
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
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



Parents
	
      
	

    • 
	
      






      
	
      
		
      
							
					
      
		
      
			
											
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Dec 22, 2017 10:25 PM
            
            
					
        
	
        

		
		
        
					
        HI Umesh,
        
 
        Thanks for your reply. Please see my reply in line. I don't see option to attach file here on EZone. Can you provide your mail ID so I can send you raw data captured as you requested.
        
 
        [Umesh]What does the full BW plot look like with the filter in line?
        
 
        [Dwijen] See the snapshot in below
        
 
        Full BW Spectrum with Filter Inline
        
 
        
 
        [Umesh]Also, what does the DDC spectrum look like when you remove the input signal (turn RF Off)?
        
 
        [Dwijen]See spectrum in below. Observe that Spur is still present at 48MHz
        
 
        DDC Spectrum with RF Turned Off
        
 
        
 
        [Umesh] I am afraid I dont fully understand the 48MHz = 3*375MHz - 700MHz math
        
 
        [Dwijen] Umesh, My apologies for the typo in the above math. See in below updated math
        
 
        48MHz = 2*375MHz (Second Harmonic of the Fout) - 702MHz (LO)
        
 
        Here Fout is Fs/8. Second harmonic of the Fout is 750MHz. This beats with NCO set at 702MHz
        
 
         
        
 
        To prove this I have provided another spectrum in below
        
 
        I have changed the Fs to 2.991GHz. Fout = 373.88 MHz (Fs/8)
        
 
        2*373.88 = 747.76MHz, NCO is set to 702MHz
        
 
        Spur is seen at 45.76MHz = 747.76MHz - 702MHz
        
 
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
				
						
				
				
		
		
        
			
		
        
	
        

        

        • 

	
      



Reply

        


      • 
	
        






        
	
        
		
        
							
					
        
		
        
			
											
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Dec 22, 2017 10:25 PM
            
            
					
          
	
          

		
		
          
					
          HI Umesh,
          
 
          Thanks for your reply. Please see my reply in line. I don't see option to attach file here on EZone. Can you provide your mail ID so I can send you raw data captured as you requested.
          
 
          [Umesh]What does the full BW plot look like with the filter in line?
          
 
          [Dwijen] See the snapshot in below
          
 
          Full BW Spectrum with Filter Inline
          
 
          
 
          [Umesh]Also, what does the DDC spectrum look like when you remove the input signal (turn RF Off)?
          
 
          [Dwijen]See spectrum in below. Observe that Spur is still present at 48MHz
          
 
          DDC Spectrum with RF Turned Off
          
 
          
 
          [Umesh] I am afraid I dont fully understand the 48MHz = 3*375MHz - 700MHz math
          
 
          [Dwijen] Umesh, My apologies for the typo in the above math. See in below updated math
          
 
          48MHz = 2*375MHz (Second Harmonic of the Fout) - 702MHz (LO)
          
 
          Here Fout is Fs/8. Second harmonic of the Fout is 750MHz. This beats with NCO set at 702MHz
          
 
           
          
 
          To prove this I have provided another spectrum in below
          
 
          I have changed the Fs to 2.991GHz. Fout = 373.88 MHz (Fs/8)
          
 
          2*373.88 = 747.76MHz, NCO is set to 702MHz
          
 
          Spur is seen at 45.76MHz = 747.76MHz - 702MHz
          
 
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
				
						
				
				
		
		
          
			
		
          
	
          

          

          • 


        


Children
	
        No Data