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AD7823 Production
The AD7823 is a high speed, low power, 8-bit A/D converter that operates from a single 2.7 V to 5.5 V supply. The part contains a 4.5 µs successive approximation...
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AD7823 on Analog.com

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Driving analog data convertor AD7823 with an op-amp



		

			

									
					    eyalniv4
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 7, 2012 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hello,
    
 
     I'm interested in using an op-amp to drive an AD7823 data convertor.
    
 
     Maximum gain required is about ~30, since I can use a ref voltage as low as 1.2V on the AD7823. Required bandwidth operation is 100KHz.
    
 
     I have no requirements on the op-amp except that the supply range should be between 3v to 5v. However, I do prefer to use a single supply op-amp. I'm not sure whether I should choose an op-amp with a differential output, which according to my understanding, will be more accurate (Will the AD7823 be able to work with it?) or a single ended output with a common ground to the ADC Vin- input?
    
 
     After reading some application notes I became a little bit confused with all the configurations out there and would appreciate some help...
    
 
     Thanks in advance,
    
 
     regards,
    
 
     Eyal
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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                on Oct 12, 2012 5:40 PM
            
            
					
        
	
        

		
		
        
					
        I would look at the AD8031, MAX4124 or MAX4125, LT6233, MAX4488, ADA4851 or the LT6202. They will all comfortable provide x20 amplification at 100kHz with at least a factor of 10 excess loop gain. 
        
 
        Instead of making all your signals 0V referenced you could generate a virtual ground reference somewhere between 0.1V and 0.5V above 0V and then configure the front end amp as a differential amplifer rather than a simple non-inverting amplifier. This would raise the opamp output up but a small amount, bypassing the problem of not swinging right down to ground. The ADC negative input would obviously connect to the virtual ground.
        
 
        Using a differential amplifier arrangement also provides an easy way of removing ground noise between different parts of your system.
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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													0
							
			
				
									
							        
			
			
			
          
            
			                            
                        
                on Oct 12, 2012 5:40 PM
            
            
					
          
	
          

		
		
          
					
          I would look at the AD8031, MAX4124 or MAX4125, LT6233, MAX4488, ADA4851 or the LT6202. They will all comfortable provide x20 amplification at 100kHz with at least a factor of 10 excess loop gain. 
          
 
          Instead of making all your signals 0V referenced you could generate a virtual ground reference somewhere between 0.1V and 0.5V above 0V and then configure the front end amp as a differential amplifer rather than a simple non-inverting amplifier. This would raise the opamp output up but a small amount, bypassing the problem of not swinging right down to ground. The ADC negative input would obviously connect to the virtual ground.
          
 
          Using a differential amplifier arrangement also provides an easy way of removing ground noise between different parts of your system.
          
			
          

		
		
		
		
	
          
	
          
		
          
			
		
          
	
          
	
          
		
						
						
				
						
				
				
		
		
          
			
		
          
	
          

          

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