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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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