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AD9517-0 Recommended for New Designs
The AD9517-01 provides a multi-output clock distribution function with subpicosecond jitter performance, along with an on-chip PLL and VCO. The on-chip...
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AD9517-0 on Analog.com

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AD9517 LVPECL output interface to a fanout buffer



		

			

									
					    GuiX
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Mar 23, 2015 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello everyone:
    
 
    I am using one AD9517-0 LVPECL output to drive a fanout buffer to convert the signal to two LDVS signals.
    
 
    In the AD9517-0 datasheet I can see this figure to interface LVPECL stages:
    
 
    
 
    On the other hand, in the datasheet of the fanout buffer, I can see this other configuration:
    
 
    
 
    My dessign follows the AD recomendation (first schematic) and incorporates R1 to R4 of the second schematic.
    
 
    Question: Should I keep the 100 Ohn resistor at the imput of the receiver (as proposed in the AD schematic)?
    
 
    Thanks in advance
    
 
    Regards
    
 
    GuiX
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 Clock Generation Devices
                
                                                    
                 Clock Generation and Distribution
                
                                                    
                 clock and timing
                
                                                    
                 AD9517-0
                
                                
            
    
    
    

		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    
















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 24, 2015 2:42 PM
            
            
					
      
	
      

		
		
      
					
      Dear GuiX,
      
 
      Kyle is correct. The 100ohm resistor marked with the red "X" is not needed and if you include it, you'll cut the amplitude in half.
      
 
      For Question 2, the max frequency isn't a simple number. The max speed is governed by the amplitude you require. The LVPECL outputs will toggle at 3 GHz, but waveform will be sinusoidal and the amplitude will be small. Refer to Figure 25 in the datasheet to see the amplitude vs frequency plot. The reason we spec 1.6 GHz is that it's max frequency at which there is enough amplitude so that nearly all LVPECL receivers will still function with good performance.
      
 
      The neat part about following my suggestion for driving an LVDS input using an LVPECL output is that you have four amplitude settings to choose from, and it's easy to increase the output driver amplitude in the event that you need to. LVPECL is much better at driving long traces at high frequency than LVDS.
      
 
      -Paul
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Mar 24, 2015 2:42 PM
            
            
					
      
	
      

		
		
      
					
      Dear GuiX,
      
 
      Kyle is correct. The 100ohm resistor marked with the red "X" is not needed and if you include it, you'll cut the amplitude in half.
      
 
      For Question 2, the max frequency isn't a simple number. The max speed is governed by the amplitude you require. The LVPECL outputs will toggle at 3 GHz, but waveform will be sinusoidal and the amplitude will be small. Refer to Figure 25 in the datasheet to see the amplitude vs frequency plot. The reason we spec 1.6 GHz is that it's max frequency at which there is enough amplitude so that nearly all LVPECL receivers will still function with good performance.
      
 
      The neat part about following my suggestion for driving an LVDS input using an LVPECL output is that you have four amplitude settings to choose from, and it's easy to increase the output driver amplitude in the event that you need to. LVPECL is much better at driving long traces at high frequency than LVDS.
      
 
      -Paul
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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