Products Mentioned

AD8139 Recommended for New Designs
The AD8139 is an ultralow noise, high performance differential amplifier with rail-to-rail output. With its low noise, high SFDR, and wide bandwidth, it...
Datasheet
AD8139 on Analog.com

AD8138 Production
The AD8138 is a major advancement over op amps for differential signal processing. The AD8138 can be used as a single-ended-to-differential amplifier or...
Datasheet
AD8138 on Analog.com

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AD8139 Not Working. I need help



		

			

									
					    sschekall
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 23, 2011 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I am using the AD8139 in the as shown in the attached PDF.
    
 
    Spice simulations work fine. But On the bench using +-5V supplys,  AD8138 outputs Nothing.
    
 
    What did I do wrong.
    
 
    Stan Schekall a783239d66076ba983835f6e0157fe05.pdf
    
									
			        
		
    

				
							osc_5MHZ.pdf
							
        

    
    Tags: 
                                            
                 amplifiers
                
                                                    
                 Differential Amplifiers and ADC Drivers
                
                                                    
                 ad8139
                
                                                    
                 ad8138
                
                                                    
                 Single-Ended to Differential Amplifiers
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 3, 2011 9:59 PM
            
            
					
      
	
      

		
		
      
					
      Hi Stan,
      
 
      Let me step back and ask a question, why you have selected this topology for the AD8139? While it is unique, this topology does have some disadvantages, such as being noisier that a traditional 4 resistor topology. It is not a circuit we commonly recommend or publicize; as it does not provide the best performance that can be attained by our amplifiers and can have issues as we are seeing. Going through the design equations, you’ll see the Vocm noise does not get cancelled out and more noise from other sources is present using this configuration. I’ve attached a slide here, that you can use to calculate and compare the two circuits. My recommendation would be to convert the circuit to a 4 resistor topology.
      
 
      cid:image001.png@01CBD9BC.548F5630
      
 
      I hope this helps
      
 
      Regards
      
 
      Jack
      
 
      From: sschekall analog@sgaur.hosted.jivesoftware.com
      
 
      Sent: Thursday, March 03, 2011 12:42 PM
      
 
      To: Ardizzoni, John
      
 
      Subject:  New message: "AD8139 Not Working. I need help" 
      
 
      Analog Devices EngineerZone<https://ez.analog.com/index.jspa>
      
 
      AD8139 Not Working. I need help
      
 
      reply from sschekall<https://ez.analog.com/people/sschekall> in Differential Amplifiers - View the full discussion<https://ez.analog.com/message/20319#20319
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 3, 2011 9:59 PM
            
            
					
      
	
      

		
		
      
					
      Hi Stan,
      
 
      Let me step back and ask a question, why you have selected this topology for the AD8139? While it is unique, this topology does have some disadvantages, such as being noisier that a traditional 4 resistor topology. It is not a circuit we commonly recommend or publicize; as it does not provide the best performance that can be attained by our amplifiers and can have issues as we are seeing. Going through the design equations, you’ll see the Vocm noise does not get cancelled out and more noise from other sources is present using this configuration. I’ve attached a slide here, that you can use to calculate and compare the two circuits. My recommendation would be to convert the circuit to a 4 resistor topology.
      
 
      cid:image001.png@01CBD9BC.548F5630
      
 
      I hope this helps
      
 
      Regards
      
 
      Jack
      
 
      From: sschekall analog@sgaur.hosted.jivesoftware.com
      
 
      Sent: Thursday, March 03, 2011 12:42 PM
      
 
      To: Ardizzoni, John
      
 
      Subject:  New message: "AD8139 Not Working. I need help" 
      
 
      Analog Devices EngineerZone<https://ez.analog.com/index.jspa>
      
 
      AD8139 Not Working. I need help
      
 
      reply from sschekall<https://ez.analog.com/people/sschekall> in Differential Amplifiers - View the full discussion<https://ez.analog.com/message/20319#20319
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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