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Adding Gain to ADC Drive Stage of LTC2387-16 - Noise and Distortion performance considerations



		

			

									
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  •  Analog Employees  

			
			
			    	
			                    
                
				                on May 13, 2021 
				
			
			
		


				
		

		    		    
		    
		    	
			
I am considering using the ADA4945-1 to drive the LTC2387-16 but need some gain at this stage to condition the signal before the ADC. Should I expect the noise and distortion to degrade if I add gain to the ADC driver circuit?

										


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[edited by: EstiS at 8:04 AM (GMT -4) on 20 May 2021]
				

					


				
				
		

			
						
									
									
						
						
			
			
			
			
		


        
        

					

			






	

		






		

			

			
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    •  Analog Employees  
    
            
			                            
                        
                on May 13, 2021 4:04 PM
            
            
					
    
	
    

		
		
    
					
    I am going to assume you are sampling the LTC2387-16 at 15 MSPS. Using the Precision ADC Driver tool you can simulate the ADA4945-1 + LTC2387-18 with and without gain and evaluate parameters like noise, distortion and settling. 
    

    A quick simulation in the ADC driver tool shows that for a gain of 2 in the ADC driver tool vs gain 1 with 50 kHz input tone there is a degradation of 1.6 dB in SNR but the THD is expected to hold up even with the gain of 2. This should be verified on the bench. 
    

    Just for your reference we have an integrated umoulde Data Acquisition Solution, the ADAQ23875, that has similar functionality as the circuit that you are implementing High Speed Fully Differential Amplifier with 16 bit 15 MSPS SAR ADC. This umodule has 0.005% precision matched resister array for the Fully Differential Amplifier. This ADAQ23875 is specified for a gain of 2 maybe similar to what you are looking for?.  The ADAQ23875 SNR for a 100 kHz input is specified at 88.5 dB with -111 dB THD.
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
						
						
				
				
		
		
    
			
		
    
	
    

    

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