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LTC5596 noise



		

			

									
					    JRP_UK
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 26, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I am trying to see if this detector could be used in the IF chain for a heterodyne radiometer application where a square-law detector is commonly used. I don't think the log-linear renders it inappropriate per se.
    

    I expect to use LNAs before the detector, but would need to have an idea of the noise contribution of the detector at the expected input power of ~-30dBm.  The spec has 22uV rms in 1 to 6.5 kHz band for 0 dBm input.  The RF input would be 4 to 20 GHz.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Mar 31, 2021 6:59 PM
            
            
					
      
	
      

		
		
      
					
      Greetings JRP,
      

      Sorry I'm not familiar with radiometer application but I'll try to answer your questions:
      

      The RF input pin of LTC5596 is internally terminated with 50 Ohms, then gets capacitor-coupled into a linear common-emitter input amplifier stage. That input amplifier stage is going to have an effective noise figure, and for best accuracy, the external LNA will need enough low-noise gain to overcome this noise figure. Sorry, we don't have an equivalent noise figure number for the input stage. I can only suggest a simple experiment of placing LNA in front of the LTC5596 and see how much gain is needed to start raising the output by almost 1dB per dB of LNA gain. 
      

      Hope this is of some help. For the internal details of LTC5596 we direct you to the US Patent disclosure on page 1 of the datasheet.   -Bruce H. 
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													+1
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Mar 31, 2021 6:59 PM
            
            
					
      
	
      

		
		
      
					
      Greetings JRP,
      

      Sorry I'm not familiar with radiometer application but I'll try to answer your questions:
      

      The RF input pin of LTC5596 is internally terminated with 50 Ohms, then gets capacitor-coupled into a linear common-emitter input amplifier stage. That input amplifier stage is going to have an effective noise figure, and for best accuracy, the external LNA will need enough low-noise gain to overcome this noise figure. Sorry, we don't have an equivalent noise figure number for the input stage. I can only suggest a simple experiment of placing LNA in front of the LTC5596 and see how much gain is needed to start raising the output by almost 1dB per dB of LNA gain. 
      

      Hope this is of some help. For the internal details of LTC5596 we direct you to the US Patent disclosure on page 1 of the datasheet.   -Bruce H. 
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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