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ADG1408 Production
The ADG1408/ADG1409 are monolithic iCMOS® analog multiplexers comprising eight single channels and four differential channels, respectively. The ADG1408...
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ADG1408 on Analog.com

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ADG1408: What leads to the high noise contribution with this analog multiplexer?



		

			

									
					    Kepa
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 13, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi, I am new to this board and I am still trying to find my way around.
    

    Here's my question:
    

    For audio processing purposes, I would like to use a programmable gain stage based on the 8:1 multiplexer ADG1408 and get a qualitative feel for the performance by comparing it against a fixed gain stage. When I look at the time domain, I see pretty good correspondence between the two gain stages. However, when I compare the noise performance, I see a 20x higher noise with the programmable gain stage. Is this really to be expected? Why is it so high? I've added the asc file add the bottom of this post..
    

     
    

     
    

    

    

    6840.mwe2.asc
    
										

    
				Fixed typo
    
[edited by: Kepa at 8:48 PM (GMT -5) on 13 Dec 2021]
				
    
						
			        
		
    

				
						
        

    
    Tags: 
                                            
                 Dual-Supply Analog Switches and Multiplexers
                
                                                    
                 adg1408
                
                                                    
                 Analog Switches Multiplexers
                
                                                    
                 switches and multiplexers
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                                                                                                                        
            
				
			
            
					
      
	
      

		
		
      
					
      Hi,
      

      Thanks for your patience.
      

      I like to ask why you are analyzing the noise of the mux_gain output to the digital EN logic, V1 input of the ADG1408?
      

      I have tried simulating the noise of the mux_gain of the amplifier with the ADG1408 connected and disconnected w.r.t. the V9 input and, I don't see any significant difference.
      

      Best regards,
      Christian
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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						in reply to Christian
					
									
        
	
        

		
		
        
					
        My apologies for the late reply. The notification from ADI went in my spam folder and since I moved on to the LTC6912, I didn't have the need to monitor this thread.
        

        In any case: does it really matter which voltage source I use as a reference? I have switched from V1 to V9 but see no difference. The noise hovers at around 14 µV/sqrt(Hz) when the mux is used, whereas the reg_mux node shows only about 700 nV/sqrt(Hz).
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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						in reply to Christian
					
									
          
	
          

		
		
          
					
          My apologies for the late reply. The notification from ADI went in my spam folder and since I moved on to the LTC6912, I didn't have the need to monitor this thread.
          

          In any case: does it really matter which voltage source I use as a reference? I have switched from V1 to V9 but see no difference. The noise hovers at around 14 µV/sqrt(Hz) when the mux is used, whereas the reg_mux node shows only about 700 nV/sqrt(Hz).
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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