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The ADAU1401A is a complete, single-chip audio system with 28-/56-bit audio DSP, ADCs, DACs, and microcontroller-like control interfaces. Signal processing...
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ADAU1401A Noise level difference in case of Analog IN and Digital IN

		
	
				

			

									
					    TomY
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Aug 28, 2024 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  ADAU1401A  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hi, ADI Support Team
    

    

    I am currently investigating the difference in noise levels at output between the analog and digital inputs of the ADAU1401A.
    

      
    

    When mute (No Slew) is executed during analog input, POP noise occurs.
    

    On the other hand, when mute (No Slew) is executed during digital input, POP noise does not occur.
    

     
    

    For the purpose of this investigation, a silent source is used for the analog input.
    

    With a normal music source, the POP noise is not noticeable, but with a silent source, it is clearly audible.
    

    Furthermore, as an additional investigation, I have removed as much noise components as possible from the analog input source, but POP noise is still detected.
    

     
    

    Does this mean that the conversion noise in the ADC is dominant over the noise of the analog input source?
    

    Is this the performance limit of the built-in ADC of the ADAU1401A?
    

     
    

    Ultimately, I intend to use mute (with Slew) to avoid this, but I need to understand the root cause.
    

    I would appreciate your opinion.
    

    

    Best Regards, TomY
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Aug 28, 2024 10:47 AM
            
            
						
			            		
      
		
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      Hello TomY.
      

      

      Every ADC converter is not perfect and will have a DC offset. Pretty much all ADCs have an internal High Pass Filter (HPF)  that can be enabled to remove it. However, the designers of this part decided to not include that in the design of the ADC. I guess they figured there is a DSP so why do this in the ADC? If I were on that design team I would have shouted from the rooftops to include it! 
      

      So that said, This is one of the few things I can complain about with this part. It is such a great part in so many ways. 
      

      This is what you need to do:
      

       
      

      

      Add a DC block filter. You can find the DC Block filters in the miscellaneous filters section of the toolbox. 
      

      If you were to have added a meter on the input of your project you would have seen the DC offset on the meter. 
      

      There is nothing wrong with the design or with your part. It is a normal issue with all ADCs. 
      

      You will see these in all of my projects and in other people's projects on the forum. 
      

      Dave T
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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    • 
	
      



	
			
		
	



      
	
      
		
      
							
					
      
		
      
		    
		    		    
			
				
									
							        
			
			
			
      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Aug 28, 2024 10:47 AM
            
            
						
			            		
      
		
										0
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      Hello TomY.
      

      

      Every ADC converter is not perfect and will have a DC offset. Pretty much all ADCs have an internal High Pass Filter (HPF)  that can be enabled to remove it. However, the designers of this part decided to not include that in the design of the ADC. I guess they figured there is a DSP so why do this in the ADC? If I were on that design team I would have shouted from the rooftops to include it! 
      

      So that said, This is one of the few things I can complain about with this part. It is such a great part in so many ways. 
      

      This is what you need to do:
      

       
      

      

      Add a DC block filter. You can find the DC Block filters in the miscellaneous filters section of the toolbox. 
      

      If you were to have added a meter on the input of your project you would have seen the DC offset on the meter. 
      

      There is nothing wrong with the design or with your part. It is a normal issue with all ADCs. 
      

      You will see these in all of my projects and in other people's projects on the forum. 
      

      Dave T
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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