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Strange things with AD9281



		

			

									
						nigelwright7557
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Sep 16, 2019 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I am using the ad9281 as the basis for a USB oscilloscope.
    

    The first problem is noise if I go above 10MHz clocking.
    

    If I reduce the clock speed the noise goes down.
    

    The other problem is with 1 volt in I am getting code 166 out when it should be 128.
    

    Vref is 2 volts.
    

    I am using a PIC micro to clock the a2d then I just read data in to PIC port b so its pretty basic really.
    

    Any advice would be appreciated.
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

					
    
			
    


    

	















    
	
    
	
    
					



			








	
	
	
	



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													0
							
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Sep 18, 2019 11:02 PM
            
            
					
        
	
        

		
		
        
					
        I got stuck into the various problems with my system.
        

        1/ My op amp circuit was too close to the PIC clock circuit and was picking up 8MHz.
        

        2/ AD9283 required better decoupling.
        

        3/ The /AIN pin is not biased centrally and I had to put an extra resistor in two bias it centrally.
        

        4/ The PIC clock seems to interfere with the AD9283 clock and using a different frequency PIC clock resulted in much less noise.
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
						
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Sep 18, 2019 11:02 PM
            
            
					
          
	
          

		
		
          
					
          I got stuck into the various problems with my system.
          

          1/ My op amp circuit was too close to the PIC clock circuit and was picking up 8MHz.
          

          2/ AD9283 required better decoupling.
          

          3/ The /AIN pin is not biased centrally and I had to put an extra resistor in two bias it centrally.
          

          4/ The PIC clock seems to interfere with the AD9283 clock and using a different frequency PIC clock resulted in much less noise.
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
						
						
				
				
		
		
          
			
		
          
	
          

          

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