• State Verified Answer
  • Replies 4 replies
  • Subscribers 47 subscribers
  • Views 1132 views
  • Users 0 members are here
Options
Similar Content 

        

            Post
             Go back to editing
        

    

    


    

    









		











	
	
			
	
			
		
	
	
		

		
Noisy AD9951 output



		

			

									
						HagertyJD
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jun 20, 2012 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I have built nearly 300 AD9951 boards that have been very successful. However, when I had
    
 
    new boards made, I ordered (40) 9951's and had a reputable SMT house install them. Building two boards
    
 
    showed an extremely noisy signal (clock noise). With a low-voltage ohm-meter I checked an old
    
 
    (bare- only 9951's and 1.8 volt regs) board against a new one, just going through the traces
    
 
    (no measurable resistance in the traces or grounds), the solder joints (small but negligible
    
 
    resistance) and then the chip to ground. Here is what I found:
    
 
             Clock input of 9951 to ground:  old board, 500K ohms, new board: 520K ohms
    
 
            1.8 volt regulator output (through 9951) to ground: old board, 48.5K ohms, new board: 50K ohms, etc.
    
 
     The resistance through the chip is different, indicating a possible change in the chip mask or something
    
 
    of that sort. The new chips exhibit a consistently higher resistance. The marking on the chip is as follows:
    
 
                                                              AD9951
    
 
                                                              YSVZ
    
 
                                                           $  208
    
 
                                                              2305722.1
    
 
    Is there a way of finding out if these chips were changed in any way? I imagine you have field data. 
    
 
    I need to resolve this issue right away and I would appreciate any guidance you can give. There seems
    
 
    to be a significant change in this batch of AD9951s. Several old and new boards give exactly the same
    
 
    results. Also, I had A.C. re-flow the soldering, but I measured the same results.
    
 
                                                    Jim H.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

					
    
			
    


    

	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



Parents
	
      
	

    • 
	
      



	
		
	
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Jun 23, 2012 10:21 PM
            
            
					
        
	
        

		
		
        
					
        Thank you for the reply, I certainly appreciate it. I will get some waveform photos (old vs. new board) and when I borrow 
        
 
        a spectrum analyzer next week I will photograph the plots and send them along. I am not using the comparator to
        
 
        square up the DAC output. The current DAC output is configured like the 9954 eval board, with the Mini-Circuits
        
 
        transformer and 51 ohm bias resistors going to 1.8 volts analog. This is where the clock noise first appears. I am
        
 
        using a 134.2177 MHz clock. I have had this configuration for years with no trouble until now. The signal then goes
        
 
        to a SMT filter and then a 20 dB amp using the AD8005. In the past this circuit has worked great. I don't know why
        
 
        the new batch of chips are showing higher resistance through the IC. More next week when I get the photos, and
        
 
        thank you for your help very much. The board comes up at 10 MHz and in the past has been clean with very little
        
 
        clock "fuzz."  The output filters cut off at 30 MHz.  Jim
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

        • 

	
      



Reply

        


      • 
	
        



	
		
	
	



        
	
        
		
        
							
					
        
		
        
			
													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Jun 23, 2012 10:21 PM
            
            
					
          
	
          

		
		
          
					
          Thank you for the reply, I certainly appreciate it. I will get some waveform photos (old vs. new board) and when I borrow 
          
 
          a spectrum analyzer next week I will photograph the plots and send them along. I am not using the comparator to
          
 
          square up the DAC output. The current DAC output is configured like the 9954 eval board, with the Mini-Circuits
          
 
          transformer and 51 ohm bias resistors going to 1.8 volts analog. This is where the clock noise first appears. I am
          
 
          using a 134.2177 MHz clock. I have had this configuration for years with no trouble until now. The signal then goes
          
 
          to a SMT filter and then a 20 dB amp using the AD8005. In the past this circuit has worked great. I don't know why
          
 
          the new batch of chips are showing higher resistance through the IC. More next week when I get the photos, and
          
 
          thank you for your help very much. The board comes up at 10 MHz and in the past has been clean with very little
          
 
          clock "fuzz."  The output filters cut off at 30 MHz.  Jim
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

          • 


        


Children
	
        No Data