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AD7608 Production
The AD7608 is an 18-bit, 8-channel simultaneous sampling, analog-to-digital data acquisition system (DAS). The part contains analog input clamp protection...
Datasheet
AD7608 on Analog.com

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SNR Measurements in datasheet

		
	
				

			

									
					    sindrekvam
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 1, 2024 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  AD7608  
    
    		        		    		    
    
		    		    
		    			
    
			    
    Hey,
    

    Figure 19 in the datasheet for the AD7608 is showing results of signal to noise ratios that can be expected with different oversampling rates.
    

    Is it possible to get any information on how this is measured?
    I have the development board EVAL-AD7608SDZ, I assume that there has to be fitted a resistor shorting the pins of the SMB connector (R5 in schematic screenshot below). 
    If this is the case, do I short with 1Mohm resistor to match the input impedance of of the ADC, or to short it directly with 0 ohms.

    

    Appended:
    

    - Figure 19 from AD7068 datasheet
    - Screenshot of V1 SMB connector from EVAL-AD7608SDZ schematics
    

      
    
			
    
			
									
		                             
                        

    
    
                                            
                 Datasheet/Specs
                
                                                    
                 Simultaneous Sampling A/D Converters
                
                                                    
                 Precision A/D Converters
                
                                                    
                 ad7608
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                        
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 2, 2024 8:35 AM
            
            
						
			            		
      
		
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      Hi,
      

      

      I'll look into this and get back to you.
      

      

      Regards,
      Jo
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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      •  Super User  
      
            
						
                            
            
            				
            
                on Jul 3, 2024 6:20 AM
            
            
						
			            		
      
		
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      sindrekvam said:
      do I short with 1Mohm resistor to match the input impedance of of the ADC, or to short it directly with 0 ohms
      

      You can short it with 0 ohms. But this gives too good results and not realistic ones.
      Keep in mind that your actual source impedance has inherent noise level too, that adds to your ADC SN.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Jul 3, 2024 8:07 AM
            
            
												
						in reply to Alexxx
					
										
			            		
        
		
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        Will I then expect better results than showed in the datasheet?
        What setup do I need to reproduce the results that are showed in the datasheet?
        

        

        I have done some measurements and I'm wondering if they are correct.
        

        The signals are generated by a RSDG805 Waveform generator, and the noise referenced is measured by shorting R5 with a 0 ohm resistor.
        

        I am getting a difference in results based on if I remove DC offset of the noise signal in post-processing of the data
        Why is it that I am measuring a DC offset when shorting the differential outputs to ground?
        

        

        Appended:
        

        - Screenshot of SNR calculated with and without DC offset removal
        

          
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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