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ADF4159 Recommended for New Designs
The ADF4159 is a 13 GHz, fractional-N frequency synthesizer with modulation and both fast and slow waveform generation capability. The part uses a 25-bit...
Datasheet
ADF4159 on Analog.com

ADF5901 Recommended for New Designs
The ADF5901 is a 24 GHz Tx monolithic microwave integrated circuit (MMIC) with an on-chip, 24 GHz VCO with PGA and dual Tx channels for radar systems....
Datasheet
ADF5901 on Analog.com

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Muxout



		

			

									
					    Vru
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jun 26, 2024 
				
			
			
		
    

				
		
    
		    		    
		    
		    		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  ADF5901  
    
    		        		    		    	
			
    Hi, 
    

    We are using ADF4159 and ADF5901 for generating 24 GHz signal. The output from the TX1 port of ADF5901 has been monitored and found to be at 24 GHz but the amplitude level was very low (- 40 dBm). Upon further digging for the root cause we have captured the 5901 Muxout for various inputs in Register R3 ( Low, High, Tristate, R divider, N divider, R/2 and N/2 dividers). For all these inputs the Muxout value is always high at 3.3V. Its quiet strange to see this as the Vtune voltage was 1.08V and the PLL Muxout showed Lock Detect as high.
    

    Is the problem the clock driving the 5901 IC or has the IC gone bad?
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 hardware
                
                                                    
                 Microwave and mmWave Transmitters
                
                                                    
                 RF Integrated Transmitters
                
                                                    
                 Fractional-N PLL
                
                                                    
                 adf5901
                
                                        
                                            
                
                
                                
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      Hi Vru, 
      

      There might be an issue with SPI clocking if MUXOUT doesn't respond to the settings changes. Can you verify SPI communications with an oscilloscope?
      

       Seeing a -40dBm at the output of the ADF5901 might mean that the output is disabled or the chip is faulty. Therefore, you need to be sure that SPI communication is working as expected and tx path of the ADF5901 can be enabled. 
      

      Can you measure the N-Divider output of the ADF4159 from mux out via oscilloscope to see if Lock is correct? It should have the same frequency as the R-Divider. 
      

      Thanks,
      

      Emrecan 
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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						in reply to emrecangidik
					
									
        
	
        

		
		
        
					
        Hi Emrecan, 
        

        Thanks for the reply.
        

        We are suspecting the clock given to the REFin. Is the SPI communication dependent on this clock? I mean if the clock is "bad" then does the device turn deaf to SPI communication?
        

        We have checked the N divider of ADF4159 through program which was streaming as 0. We thought that the 12 GHz Aux input drive isn't sufficient to drive (which is around -20 dBm) therefore N divider output is zero. R divider is coming out perfectly as expected.
        

        Same crystal is used to ac couple to ADF4159 and ADF5901 for their respective REFins. 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													+1
							
			
				
									
							        
			
			
			
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						in reply to Vru
					
									
        
	
        

		
		
        
					
        Hi Vru, 
        

        The Aux level is also very low. It is stange that ADF4159 shows lock detect. 
        

        Can you check the voltage levels on each supply pin of the ADF5902 and be sure that each supply has a sufficient level?
        

         
        

        

        Thanks,
        

        Emrecan
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
						
				
				
		
		
        
			
		
        
	
        

        

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						in reply to emrecangidik
					
									
          
	
          

		
		
          
					
          Hi Emrecan,
          

          The ADF5901 which I used was faulty. I replaced it with a new one.
          

          However my ordeal with the chip has not ended. I have programmed to get a 24GHz output. The output from ADF5901 is  coming at 24 GHz with power of -4dBm. The PFD frequency of ADF4159 is 10 MHz. The R divider output of muxout is monitored and found to be ok. But the N divider output is coming as zero. Aux output of ADF5901 is ac coupled to ADF4159. Aux bar output is grounded.
          

          What is that I am seriously messing with and How to get my PLL locked?
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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