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Sigma-Delta ADC low frequency attenuation



		

			

									
						viliamklein
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Apr 9, 2016 
				
			
			
		


				
		

		    		    
		    
		    	
			

I have a simple question about sigma-delta converters. I've noticed a lot of the products seem to have filters designed attenuate low frequencies. For example, the AD7781 datasheet shows -50dB gain for a 10Hz signal (see image). For my application, I would like to measure some low frequencies out of a pressure sensor. Should I really expect to see -50dB attenuation if my source is a 10Hz wave?

 

 
Thanks for your help!

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	

		
	











	

	

					



			








	
	
	
	



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                                 Analog Employees 
                                
                            
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                on Apr 10, 2016 7:32 PM
            
            
					
    
	
    

		
		
    
					
    Hi, VilliamKlein.
    
 
    For AD7781, the filter response for output data rate of 16.7Hz shows a -50dB attenuation, but this notch is for frequency around 8.5Hz. For 10Hz, you will be expecting around -13dB attenuation. Sigma delta ADC are intended for high precision, very low frequency applications. Thus, the digital filter applies only a low pass filter which attenuates high frequency noises but also reduces the frequency bandwidth.
    
 
    Thanks,
    
 
    Jellenie
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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													0
							
			
				
									
							        
            
                                                                                                        
      
                            
    • 
                                 Analog Employees 
                                
                            
      • 
                        
     
                                                           			
			                            
                        
                on Apr 10, 2016 7:32 PM
            
            
					
    
	
    

		
		
    
					
    Hi, VilliamKlein.
    
 
    For AD7781, the filter response for output data rate of 16.7Hz shows a -50dB attenuation, but this notch is for frequency around 8.5Hz. For 10Hz, you will be expecting around -13dB attenuation. Sigma delta ADC are intended for high precision, very low frequency applications. Thus, the digital filter applies only a low pass filter which attenuates high frequency noises but also reduces the frequency bandwidth.
    
 
    Thanks,
    
 
    Jellenie
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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