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reference of AD9245



		

			

									
						major.zhao
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Dec 12, 2017 
				
			
			
		


				
		

		    		    
		    
		    	
			
We use AD9245 to sample the signal detect single end amplifier with output voltage from 0 to 2 volts.  We connect this output to Vin+. My question is that should we connect the Vin- to ground or to a voltage reference of 1 volt. If we connect the Vin- to ground, the differential input of AD9245 will be from 0 to 2 volts. If we connect the Vin- to 1 volt reference,  the differential input of AD9245 will be from -1 to 1 volt.  Could you please tell us which solution is right or both are right?

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	

		
	











	

	

					



			








	
	
	
	



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                                 Analog Employees 
                                
                            
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                on Apr 30, 2018 10:25 PM
            
            
					
    
	
    

		
		
    
					
    Hello,
    
 
    If you run AD9245 at 1V internal reference by connecting SENSE pint to ground and bias VIN- with 1V VREF, you shouldn't need 1K ohm to ground on VIN- side.  The source impedance on each inputs should be well matched in order to achieve the best possible performance.
    
 
    Questions are : When you say " change target half", what does that mean? Does it mean to set VIN+=0.5V = 1/2 VIN- ?
    
 
                              How do you set the output common mode voltage on AMP output(=VIN+ of AD9245)?
    
 
                             
    
 
    The digital code "0" covers within +/- 1/2 LSB (61uV here) and offset error of AD9245 on datasheet is typically +/-0.3% and Max +/-1.2%  FSR @ 1.0V internal reference. Offset error at Max 1.2% case is 2V_FS*1.2*0.01=24mV. So it doesn't explain 60mV fully here. Please let me know if there is any change without 1K ohm on VIN- side.
    
 
    Thanks
    
 
    Tony  
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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													0
							
			
				
									
							        
            
                                                                                                        
      
                            
    • 
                                 Analog Employees 
                                
                            
      • 
                        
     
                                                           			
			                            
                        
                on Apr 30, 2018 10:25 PM
            
            
					
    
	
    

		
		
    
					
    Hello,
    
 
    If you run AD9245 at 1V internal reference by connecting SENSE pint to ground and bias VIN- with 1V VREF, you shouldn't need 1K ohm to ground on VIN- side.  The source impedance on each inputs should be well matched in order to achieve the best possible performance.
    
 
    Questions are : When you say " change target half", what does that mean? Does it mean to set VIN+=0.5V = 1/2 VIN- ?
    
 
                              How do you set the output common mode voltage on AMP output(=VIN+ of AD9245)?
    
 
                             
    
 
    The digital code "0" covers within +/- 1/2 LSB (61uV here) and offset error of AD9245 on datasheet is typically +/-0.3% and Max +/-1.2%  FSR @ 1.0V internal reference. Offset error at Max 1.2% case is 2V_FS*1.2*0.01=24mV. So it doesn't explain 60mV fully here. Please let me know if there is any change without 1K ohm on VIN- side.
    
 
    Thanks
    
 
    Tony  
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

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