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LTC1050 Production
The LTC1050 is a high performance, low cost zero-drift operational amplifier. The unique achievement of the LTC1050 is that it integrates on-chip the two...
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LTC1050 on Analog.com

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.step in LTspice XVII for OS X - plots show constant Vout



		

			

									
					    pgoodwin
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 24, 2020 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Maybe I'm doing something wrong, but I can't get the plots to show the change in Vout when R2 in the schematic is stepped. I can see the value of R2 being stepped in the plots, but Vout stays constant. Vout should change from 100 uV down to 1 uV as R2 is increased from min to max resistance. The CD Op point works OK (2nd and 3rd pics below). The 4th and 5th pics below show the .step issue. Does the .step function in the Mac version of LTSpice work? This is a pretty simple circuit. 
    

    

     
    

    

        1108.Pyrometer Preamp LTC1050.asc
    
										

    
				Added actual schematic file Pyrometer Preamp LTC1050.asc
    
[edited by: pgoodwin at 3:46 PM (GMT 0) on 25 Jul 2020]
				
    
						
			        
		
    

				
						
        

    
    Tags: 
                                            
                 Operational Amplifiers (Op Amps)
                
                                                    
                 amplifiers
                
                                                    
                 LTC1050
                
                                                    
                 High Voltage Op Amps =12V
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      •  Super User  
      
            
						
                            
            
            				
            
                on Jul 27, 2020 9:53 AM
            
            
												
						in reply to simonbramble
					
									
      
	
      

		
		
      
					
      you might also want to look at the LTC6244 datasheet for some really neat TIA circuits based on JFETs and op amps. This might improve your system level design. We have JFET models in LTspice - or you can import a third party model
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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                on Jul 27, 2020 11:00 AM
            
            
												
						in reply to simonbramble
					
									
        
	
        

		
		
        
					
        thanks for the info. My particular application has a need for both very low Vos and low opamp bias currents. The ambient temperature of the ambient where this would reside is close to 80C. The particular photodiode being used was chosen for a particular wavelength bandwidth. Unfortunately the photodiode leakage resistance (R2 in my schematic) can drop down to 13K or so at that high temp. So the output gain vs Vos goes from 1.0 to 75. Delta Vout vs Ibias at the (-) input is Rfdbk * delta Ibias over temp. The other constrain on this system is that there's not much supply current available - the 6244 would be a challenge just for that purpose. JFET and CMOS input opamps are definitely the way to go.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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