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LTC5594 Recommended for New Designs
The LTC5594 is a direct conversion quadrature demodulator optimized for high linearity zero-IF and low-IF receiver applications in the 300MHz to 9GHz frequency...
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LTC5594 on Analog.com

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LTC5594 IF amplifier S-parameters

		
	
				

			

									
					    FilipZ
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on May 27, 2025 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user is working on custom design for the interstage and anti-alias filter of the LTC5594 and needs to simulate the IF amplifier using s-parameters. The final answer suggests staying in s2p format with a 100Ω characteristic impedance and using ideal 180° phase combiner/splitter to create a 4-terminal device. The user's idea of creating a mixed mode matrix with zero single-ended to differential transfer is noted, and the common mode matrix is explained as indicating the common mode gain, which is not ideal for this part.
                        	    

                
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Product Number:  LTC5594  

    		        		    		    

		    		    
		    			

			    
Hi, we are working on custom design of interstage and anti-alias filter for LTC5594. We need to simulate the IF amplifier as s-params are given in datasheet (differential & common mode s2p), but are facing problems with interpreting them correctly. For simulation we need them in the form of *.s4p file, i.e. 4-port single-ended or mixed mode s-parameters. Could you give us an advice how to process the given parameters correctly? Thank you.

			

			
									
		                             
                        

    

                                            
                 Datasheet/Specs
                
                                                    
                 ltc5594
                
                                                    
                 rf & microwave
                
                                                    
                 I/Q Demodulators
                
                                                    
                 s-parameters
                
                                        
                                            
                
                
                                
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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on May 30, 2025 5:10 PM
            
            
						
			            		
    
		
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    Hi Filip,
    I don't think that it's possible to generate an s4p file from this dataset. So you need to stay in s2p format but declare in the header that the characteristic impedance is 100. Also, the header should declare that the data are magnitude and angle. Looking at the data, I think that the data is for a gain of 8 dB. If you need to have a differential symbol in your schematic, Maybe you can put an ideal 180 deg phase combiner at the input (0dB, 0/180 deg) and an ideal 180 deg splitter at the output. This will give you a 4-terminal device. 
    Best Regards
    Eamon Nash
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
				
				
				
		
		
    
			
		
    
	
    

    

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                on Jun 3, 2025 2:27 PM
            
            
												
						in reply to enash
					
										
			            		
    
		
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    Hi Eamon,
    

    thank you for the answer. I'll try it.
    

    The bad thing is I need to be 100% sure the data is interpreted correctly otherwise all design and all work could be ruined.
    

    My idea was to create mixed mode matrix as
    

    


    
DD
DC

    

    
CD
CC

    
    

    

    where DD is the differential matrix, CC is the common mode matrix, and CD&DC matrixes are zero since there is no use of single-ended to/from differential mode transfer.
    

    I am wondering why there is a common mode matrix. In the datasheet there is not pointed the use of IF amplifier in a single-ended mode, therefore common mode matrix would be useless then.
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Jun 4, 2025 11:02 AM
            
            
						
			            		
    
		
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    Hi Filip, 
    unfortunately I don't know enough about the manipulation of s-parameters to advise on whether your idea will work. Regarding the common mode s-parameters. I believe that these are expressing the common mode gain of the circuit, that is, what differential signal appears at the outupt if you apply the same signal to both input. This number should normally be -Infinity. But for this part it's not so good, almost 0dB at some frequencies. I think that this means that the part needs be be driven differentially.
    Eamon
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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