Products Mentioned

AD8624 Production
The AD8624 is a quad, precision rail-to-rail output operational amplifier with a low supply current of only 350 μA maximum over temperature and supply...
Datasheet
AD8624 on Analog.com

ADA4177-4 Recommended for New Designs
The ADA4177-1 single-channel, ADA4177-2 dual-channel, and ADA4177-4 quad-channel amplifiers feature low offset voltage (2 μV typical) and drift (1 μV...
Datasheet
ADA4177-4 on Analog.com

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compare noise ADA4177 and AD8624  in a simple circuit Input in positive op-amp input - Something wrong in model.

		
	
				

			

									
					    Politopoulos
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Feb 5, 2024 
				
			
			
		
    
		
		                     
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Datasheet/Specs
    
    		        		            		    
    Product Number:  ADA4177-4  
    
    		        		    		    
    
		    		    
		    			
    
			    
    ADA4177 noise model does not agree with datasheet at least in range 0.1Hz to 50HZ . A simple comparison with AD8624 will show it. R values can be lowered to decrease thermal noise, if RC
    

    product is constant. Even more in datasheet peak noise 0.1-10Hz is very low and not agree with calculations of Ltspice ( notice also that spice computes rms value not peak, as I know)
    

    Me and my students try to design a special biosensor. Signal is in the range of mHz to some Hz and amplitude of uV,  so is very important the noise, also protection is important.
    

    Please help us, seams to be a better selection according to datasheet but in Ltspice is worst. What is true? Or another suggestion will be helpful. 
    

    Thanks you, in advance
    

    K. Politopoulos 
    

     5824.noise-test.asc
    
			
    
			
									
		                                 
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                 Precision Op Amps (Vos ≤1mV & TCVos ≤2uV/C)
                
                                        
                                            
                
                
                                        
                                            
                
                
                                        
                                            
                
                
                                        
                                            
                
                
                                
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      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Feb 5, 2024 8:07 PM
            
            
						
			            		
      
		
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      Hi  ,
      

      Good day. We will try to look into the noise model of the part. I just had some questions regarding your inquiry:
      

        

      • What schematic did you use to measure the part's 0.1 to 10 Hz noise? 
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      • What was your measured value? 
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      Regards,
      Gilbeys
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Feb 6, 2024 2:45 AM
            
            
												
						in reply to GLADION
					
										
			            		
        
		
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        Hi
        

        I have uploaded it as file 4213.noise-test.asc  .
        

        It is very simple series rc in negative input connected to ground  plus parallel rc in feedback. Input in positive input of op-amp and gain almost 40. The real circuit is more complicate but you can see the noise in this simple circuit. It is not exactly a band pass filter but  you can format the rc values to to create a simple band pass in the range 0.1Hz to 30Hz.. Look at output noise.
        

        In datasheet p-p noise in ADA4177 noise is a little less than AD8624. In calculations (ltspice) noise near 0.1Hz  to 1Hz  with ADA4177 we have huge increase (of course 1/f noise). On the other hand series rc decreases the gain. So,  some cancellation of 1/f noise  is expected at output. This behavior (cancellation) is calculated in Ltspice if replace ADA4177 with AD8624.
        

        So what is true?
        

        Thank you for the quick answer
        

        K. Politopoulos
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        •  Super User  
        
            
						
                            
            
            				
            
                on Feb 13, 2024 7:20 PM
            
            
												
						in reply to Politopoulos
					
										
			            		
        
		
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        Hi  ,
        

        

        Good day. As verified, there was a slight discrepancy with the ADA4177 noise model as compared to the datasheet while the AD8624 noise model was indeed modeled correctly. I'll try to share this with the team for review. Thank you.
        


        Regards,
        

        Gilbeys
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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