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ADV7181C Production
The ADV7181C is a high quality, single-chip, multiformat video decoder and graphics digitizer. This multiformat decoder supports the conversion of PAL...
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ADV7181C on Analog.com

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ADV7181C High Freq. Noise Issue



		

			

									
					    KevC
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Dec 8, 2011 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi all,
    
 
    Intern here so please go easy on me.
    
 
    As you can see in the picture, the NTSC signal seem to have noise in the high frequency region. Our ADV7181C setup is nearly identitcal with the Appnotes.
    
 
    Please throw ideas at me and I can provide more information as needed. Thanks.
    
 
    Kevin
    
									
			        
		
    

				
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    Hi Kevin,
    
 
    We were all interns/rookies at some time.
    
 
    Here's a list of things I'd check:
    
 
    1) power supplies, how clean are they? Were they implemented as shown in the reference schematics?
    
 
    2) how clean is the layout?  Again refer to the reference layout.  Depending on layout noise can be injected into the source.
    
 
    3) Have you tried another source?
    
 
    4) What's the output.  It might not even be the receiver but the transmitter or monitor.  Have you tried another monitor?
    
 
    5) Can you duplicate this on our reference board? Assuming you have one.
    
 
    From the second image it's hard to believe it's a ADV7181C problem directly.  Also form the second image it doesn't appear to be a impedance mismatch on the board, rather some kind of analog noise getting coupled into the NTSC sign or possibly something is wrong with the monitor or transmitter.
    
 
    http://ez.analog.com/docs/DOC-1621http://
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
						
						
				
				
		
		
    
			
		
    
	
    

    


	

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      1. Power supplies should be clean. We isolated PVDD, AVDD and ELPF with ferrite and cap.
      
 
      2. We have the source coming from a BNC directly into pin 35 (series with the .1u cap and parallel with 75ohm to gnd). There shouldn't be any noise injected into source.
      
 
      3. I tried this source on our previous generation unit and it came out noise-less.
      
 
      4. I have tried several monitors and we have multiple setups. I'm certain it is not the monitor.
      
 
      5. I believe we do have a demo board.. I will look into that.
      
 
      Thanks!
      
 
      Kevin
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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      From the layout stand point I'm mostly worried about a solid ground plane on layer 2 with the critical routes on layer one.  Power is then distributed via split planes on layer 3,  Check out the the attached reference layout.
      
 
      Placement of the ELF components need to be as close the the part as possible.  Depending on layout and other noise you can inject video noise through those parts.
      
 
      Without looking at the schematic and layout it's hard to see what else could be wrong.  If the previous generation was prefect I'd just start by doing a complete side by side comparison.
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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        The ELF components are extremely close to the pin, I don't think placement is an issue. However, before we accidentally grounded ELPF instead of pulling up to 1.8. After we fixed that issue the noise decreased by a good amount. I'm thinking this can be the culprit here. Do you recommend changing the resister and the two cap values to further reduce noise?
        
 
        Also, I've attached the schematic, register dump, and what the 1.8V looks like before and after turning on the chip. Please let me know if you see anything that should be changed.
        
 
        Thanks,
        
 
        Kevin
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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        The spike in the 1.8V could be switching power supply noise.
        
 
        Don't change the ELP filter caps.  They need to be exactly as they are.  It's a tuned circuit.
        
 
        Is the ground plane on layer 2 and is it solid?  Other then this I'd have to says it's a layout issue or placement.  If you want I can check the layout quickly.  We can transfer it over private email instead of putting in this public forum.
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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        •  Analog Employees  
        
            
			                            
                                                                                                                        
            
				
			
            
					
        
	
        

		
		
        
					
        This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

        Thank you,
        EZ Admin
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
				
						
						
				
				
		
		
        
			
		
        
	
        

        

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