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AD8236 Production
The AD8236 is the lowest power instrumentation amplifier in the industry. It has rail-to-rail outputs and can operate on voltages as low as 1.8 V. Its...
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AD8236 on Analog.com

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Why the inputs of AD8236 need to be pulled to VDD and VCC in application of ECG measurement



		

			

									
					    laumung
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 7, 2020 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi everyone,
    

    Now I made a circuit to measure ECG based on the AD8236. I followed the example in the AD8236 manual as shown below.
    

     
    

    But when I test with electrodes connected to the human body, I found the output of AD8236 remained 2.5v. I cannot see the ECG waveform at the output of AD8236. When I removed the pull resistors at the inputs of AD8236, I can see the ECG signal at the output of AD8236 by the oscilloscope. Does that normal? Did I make any mistakes? Appreciate your help.
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 amplifiers
                
                                                    
                 Instrumentation Amplifiers
                
                                                    
                 ad8236
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Dec 8, 2020 9:50 PM
            
            
					
      
	
      

		
		
      
					
      Hi,
      

      Let me get back to you on this. In the meantime, could you elaborate the electrodes that you're using? My initial suspicion would be that the electrodes that you're using has some sort of capacitance. This capacitance together with the 953k at the inputs forms a high-pass filter that could attenuate the signal of the electrodes. You could try lowering the values of the two 953k resistors and see if that helps.
      

      A brief description about the input frequency range, and the electrodes specification would be helpful.
      

      Thanks,
      

      Donnie
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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