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Design considerations for filters in ADXUD1AEBZ (XUD1A)



		

			

									
					    highFive
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 29, 2022 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi,
    

    Are you (ADI) planning on publishing more documentation on how you designed the signal chain for the XUD1A board? What requirements you had and why you picked the specific components?
    

    We are looking to narrow the bandwidth by changing some of the filters. On the XUD1A board are 3 Mini-Circuits filters which are fairly inexpensive, but at the RF port is placed a Knowles BPF which is more than 10x as expensive as the Mini-Circuits BPF next to the mixer. Is it the pass band requirements (X-Band is 8-12 GHz) that drives the RF filter selection and/or losses, signal power, or some other quality?
    

    Can you elaborate so we are not missing a spec or quality?
    

    Thanks,
    

    Claus
    
									
			        
		
    

				
						
        

    
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      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi Claus, 
      

      

      I do plan on adding more information regarding design criteria to our wiki page for the ADXUD1AEBZ. The Knowles B096QC2S filter and the Mini-Circuits filters were chosen for frequency planning purposes. As mentioned in the webinar, this up/down converter was designed for a fixed IF architecture (IF frequency range of 4.2 GHz to 6.3 GHz) in order to direct sample in the 3rd Nyquist bin of the AD9081 ADC. The RF BPF was selected for its high rejection to attenuate mixing products and out of band interferes. Other than a custom front end filter (e.g. printed filter), there are few commercial options that cover the full X-Band spectrum with high out of band rejection. I would recommend selecting an alternate filter for the Mini-Circuits BFCN-5200 IF filter. The out of band rejection for this filter is on the order of 20 dB and doesn't provide sufficient rejection of the LO feedthrough to obtain best spurious performance of the RX signal chain.  
      

      

      Regards, 
      Sam
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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													+1
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi Claus, 
      

      

      I do plan on adding more information regarding design criteria to our wiki page for the ADXUD1AEBZ. The Knowles B096QC2S filter and the Mini-Circuits filters were chosen for frequency planning purposes. As mentioned in the webinar, this up/down converter was designed for a fixed IF architecture (IF frequency range of 4.2 GHz to 6.3 GHz) in order to direct sample in the 3rd Nyquist bin of the AD9081 ADC. The RF BPF was selected for its high rejection to attenuate mixing products and out of band interferes. Other than a custom front end filter (e.g. printed filter), there are few commercial options that cover the full X-Band spectrum with high out of band rejection. I would recommend selecting an alternate filter for the Mini-Circuits BFCN-5200 IF filter. The out of band rejection for this filter is on the order of 20 dB and doesn't provide sufficient rejection of the LO feedthrough to obtain best spurious performance of the RX signal chain.  
      

      

      Regards, 
      Sam
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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