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ADG918 Production
The ADG918/ADG919 are wideband switches using a CMOS process to provide high isolation and low insertion loss to 1 GHz. The ADG918 is an absorptive (matched...
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ADG918 on Analog.com

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Cascading Analog Switches

		
	
				

			

									
					    KSM1
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jul 4, 2025 
				
			
			
		
    
		
		                    	    
    
        	    
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                The user is seeking a SP8T switch with a bandwidth of about 5 GHz and a switching time <5ns. The ADG918 (4 GHz, 6.6 ns) is considered, and cascading 3 stages is proposed to achieve the SP8T configuration, with an expected -3 dB point at 2.5 GHz. The ADRF5042 (100 MHz to 44 GHz, 3 ns rise/fall time) was suggested but has a higher knee frequency. The user will proceed with the ADG918 cascade, considering the insertion loss and isolation trade-offs.
                        	    
    
                
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    Category: Hardware
    
    		        		            		    
    Product Number:  ADG918 
    
    		        		    		    
    
		    		    
		    			
    
			    
    I am looking for a SP8T switch with a bandwidth about 5GHz to be used in a custom test system. GaAs MMICs have ample bandwidth but switching time is too slow (>100ns). Required switching time is <5ns. ADG918 (4GHz, 6.6ns) should be usable with some reduced margins but it's a SPDT. I'm thinking to cascade them in 3 stages to get a SP8T. Any thoughts and suggestions on this would be much valued.
    
			
    
			
									
		                             
                        

    
    
                                            
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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jul 4, 2025 5:26 AM
            
            
						
			            		
      
		
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      Hi,
      

      Thanks for your query and interest on the ADG918. You can use 7 x ADG918 to build an SP8T. It depends on how much insertion loss and level of isolation your application can tolerate. Say at 4 GHz, isolation is at -10 dB and insertion loss is ~-3 dB x 3 = ~-9 dB.
      

      Can you advise what frequency will your signal be at?
      

      We have MEMS switches like the ADGM1144 that goes up to 18 GHz. It's an SP4T switch, so 3 of these will be enough for an SP8T configuration. At 4 GHz, insertion loss is around 0.5 dB x 2 = 1 dB.
      

      regards, Francis
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
				
				
				
		
		
      
			
		
      
	
      

      

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                on Jul 7, 2025 3:00 AM
            
            
						
			            		
        
		
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        Hi Francis,
        

        Thanks for your reply. Generally, my signal will have a bandwidth of DC to 2.5GHz. Ideally, I would like to have flattest possible response for that range. Having said that, it would be acceptable to have -3dB at 2.5GHz. 3 stages of ADG918 would give -3dB at 2GHz and; at 2.5GHz, it would be down about 3.3dB (taking baseline insertion loss of 0.4dB per stage). That is still okay considering no other alternatives. I'd also like to know if you would recommend buffers/amplifiers between stages.
        

        Can you also elaborate on how isolation of -10dB is arrived at?
        

        Thanks also for suggesting MEMS switches. Their bandwidth is very impressive but switching time is way too slow. 200us is definitely a no no.
        

        Best regards,
        

        - KSM
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
						
                            
            
            				
            
                on Jul 9, 2025 12:03 PM
            
            
						
			            		
        
		
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        Hi Francis,
        this fastest silicon RF switch I can see is ADRF5042. It operates from 100 MHz to 44 GHz. Rise/Fall time is 3ns. It takes 14ns from 50% of VCTRL to RF output at 90%. Settling to 0.1 dB and 0.05 dB is 30ns and 36ns respectively (from 50% of VCTRL).
        Eamon 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
				
				
				
		
		
        
			
		
        
	
        

        

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                on Jul 13, 2025 11:51 PM
            
            
						
			            		
          
		
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          Hi Eamon,
          

          Thanks for suggestion on ADRF5042. The switching times look good but I need a lower knee down to DC or very close (probably <5MHz).
          

          I think my doubts on whether it is advisable to build a SP8T out of SPDTs have been clearer now and I am proceeding with it with adjustments in all possible angles to get an optimal circuit.
          

          Thanks for the help.
          

          Best regards,
          

           - KSM
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
				
						
				
				
				
		
		
          
			
		
          
	
          

          

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