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Simulation difference LTSpice 24.0.9 and 24.1.x (for Windows)

		
	
				

			

									
					    StevenBos
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 17, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user encountered issues with ambiguous models and simulation differences in LTspice version 24.1.10 compared to 24.0.9. The model conflict can be resolved by renaming the custom model, and the voltage offset is due to C1's right pin not being connected, which was incorrectly handled in the earlier version. Adding a 100 MΩ resistor to ground after C1 emulates the desired effect.
                        	    
    
                
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    Category: Software
    
    		        		        		        		        
    Software Version: 24.1.10
    
    		    		    
    
		    		    
		    			
    
			    
    The latest LTspice versions (eg.  24.1.10) for windows seem to behave differently compared to 24.0.9 with at least the following 2 issues found:
    

    

    - ambiguous models. This can be fixed with a simple rename, but this was not a problem before when defining a custom model (see eg. file below)
    

    - simulation difference. In the circuit below input and output are not identical but have an offset of about -1.8V

    A test file : cmos_source_follower.asc
    
			
    
			
									    
    
			        
    Edit Notes
    
    				spelling mistake
    
[edited by: StevenBos at 9:38 AM (GMT -4) on 17 Oct 2025]
				
    
						
		                             
                        

    
    
                                            
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                 24.0.9
                
                                                    
                 LTspice
                
                                                    
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Oct 17, 2025 8:07 AM
            
            
						
			            		
      
		
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      Dear  ,
      

      LTspice always puts the line
      

      .model NMOS NMOS
      

      in the netlist if an nmos device is present. That's the cause of your model name conflict. A netlist with duplicate model names is ill-formed. Former LTspice versions were simply wrong to accept that.
      

      The voltage difference you observe is due to C1. It's right pin is not connected anywhere. Thus, no current can ever flow in C1, thus the voltage across C1 is always 0. Thus, the result you get from 24.0.9 is incorrect.
      

      Best Regards,
      Mathias
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
						
						
				
				
		
		
      
			
		
      
	
      

      

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                on Oct 21, 2025 4:02 PM
            
            
												
						in reply to mborn
					
										
			            		
        
		
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        Makes sense, i´ll update the name to ANMOS or MYNMOS or similar. 

        We wanted to remove the DC component with C1. By adding a 100 M resistor to ground after C1 to emulate a scope we get the same effect as we had with 24.0.9. I wonder why 24.0.9 worked though!
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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