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AD9680 Recommended for New Designs
The AD9680 is a dual, 14-bit, 1.25 GSPS/1 GSPS/820 MSPS/500 MSPS analog-to-digital converter (ADC). The device has an on-chip buffer and sample-and-hold...
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AD9680 PN Sequence Issues



		

			

									
					    nonvolatile
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 26, 2023 
				
			
			
		
    

				
		
    
		    		    
		    
		    		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  AD9680 
    
    		        		    		    	
			
    Hello,
    

    

    I have the AD9680 setup in the following configuration: 
    

     
    

    I am able to run and successfully verify all the ADC Test Patterns, except the PN23 and PN9 test modes from the ADC. I am even noticing correct JESD Interface PN23 and PN9 sequences at my ILA in the FPGA, but for some reason I am not seeing the expected sequences for the ADC PN test modes. I think I am not understanding something correctly...
    

    Here is a snapshot of the ILA, where I am only looking at Converter 0 (m0) samples:
    

     
    

    I triggered on 0x125B in the above image for PN9, but then I don't see the next value of 0x3C9A anywhere close. is the PN sequence being copied and sent out on each Lane and sample like below:
    

     
    

    Or Should I expect it to be sequential like this:
    

     
    

    Or something else? I am confused though, because I am able to trigger on other sequence values, but they don't look close to one another... 
    

    

    Thanks
    
									
			        
		
    

				
						
        

    
    Tags: 
                                            
                 ad9680
                
                                                    
                 hardware
                
                                                    
                 High Speed A/D Converters >10 MSPS
                
                                                    
                 Standard High Speed A/D Converters
                
                                                    
                 pn23
                
                                        
                                            
                
                
                                
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													0
							
			
				
									
							        
			
			
			
        
            
						
                            
            
            				
            
                on Feb 1, 2023 12:15 PM
            
            
					
        
	
        

		
		
        
					
        So, im noticing that once I put the ADC in 14-bit mode, which is the pure resolution of the ADC, I get the right sequences in bits 15:2, as noted in the datasheet. But with my configuration shown above its actually 16-bits since the DDCs output 16-bits. In this case, does the PN sequences change? Should I be using a 16-bit output for the PN9 and 23 sequences? Which also changes how many times to shift the PN9? 
        
			
        

		
			
	      

		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													+1
							
			
				
									
							        
			
			
			
          
            
						
                            
            
            				
            
                on Feb 2, 2023 4:12 PM
            
            
												
						in reply to nonvolatile
					
									
          
	
          

		
		
          
					
          I figured it out. While using the DDCs, the output is 16bits and the PN sequences use a 16bit output. I was having issues figuring out why the PN23 sequence still wasnt looking right...but it was because I was triggering on one of the first words in the sequence, but since we only see 16-bits of the 24-bit sequence, that 16-bit word I was triggering on actually shows up multiple times and was in a random part of the sequence, not the start like I expected. 

          Once I triggered on 2 back to back 16-bit words that I expected, the rest of the sequence looked right.
          
			
          

		
			
	      

		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
						
						
				
				
		
		
          
			
		
          
	
          

          

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													+1
							
			
				
									
							        
			
			
			
            
            
						
                            
            
            				
            
                on Feb 2, 2023 4:12 PM
            
            
												
						in reply to nonvolatile
					
									
            
	
            

		
		
            
					
            I figured it out. While using the DDCs, the output is 16bits and the PN sequences use a 16bit output. I was having issues figuring out why the PN23 sequence still wasnt looking right...but it was because I was triggering on one of the first words in the sequence, but since we only see 16-bits of the 24-bit sequence, that 16-bit word I was triggering on actually shows up multiple times and was in a random part of the sequence, not the start like I expected. 

            Once I triggered on 2 back to back 16-bit words that I expected, the rest of the sequence looked right.
            
			
            

		
			
	      

		
		
	
            
	
            
		
            
			
		
            
	
            
	
            
		
						
						
						
						
				
				
		
		
            
			
		
            
	
            

            

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