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AD7942 signed output



		

			

									
					    thejashree
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Aug 5, 2021 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    Hi Team,
    

    We are using EVAL-AD7942-PMDZ in our system.
    

    We are giving 50Hz phase signal as a input to the ADC and we have phase calculation to be done in the FPGA.
    

    For this requirement we need to have signed digital data to be output from the ADC. So we just wanted to understand what is the format of the data coming from the AD7942.
    

    We have following queries on the same.
    

    1) Whether this ADC will output signed digital data?
    

    2)How to configure the ADC to output signed data?
    

    With regards,
    Thejashree
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Aug 5, 2021 2:16 PM
            
            
					
      
	
      

		
		
      
					
      Hi Thejashree,
      

      Thanks for your query.
      

      The AD7942 is a pseudo-differential ADC, meaning it samples a single-ended signal relative to IN- (which is nominally tied to ground). As such, the output data is unsigned, and there are no options to have it output signed data.
      

      Our fully-differential ADC equivalents do output signed data, but only because it converts the differential voltage of IN+ - IN- which can be negative when IN- is higher than IN+. But these devices do typically require single-ended to differential conversion in the analog domain, for example using a fully-differential amplifier, etc. They require a differential input signal with common mode voltage of VREF/2, it doesn't work if you tie IN- to ground and treat IN+ as a single-ended input.
      

      The closest fully-differential ADC equivalent to the AD7942 is the AD7687. The AD7687 outputs 16-bit signed data.
      

      Can you explain the nature of the 50Hz wave you're measuring? Is it unipolar or bipolar? What is the amplitude?
      

      Also, why does the data coming out of the ADC need to be signed?
      

      Thanks,
      

      Tyler
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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													+1
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Aug 5, 2021 2:16 PM
            
            
					
      
	
      

		
		
      
					
      Hi Thejashree,
      

      Thanks for your query.
      

      The AD7942 is a pseudo-differential ADC, meaning it samples a single-ended signal relative to IN- (which is nominally tied to ground). As such, the output data is unsigned, and there are no options to have it output signed data.
      

      Our fully-differential ADC equivalents do output signed data, but only because it converts the differential voltage of IN+ - IN- which can be negative when IN- is higher than IN+. But these devices do typically require single-ended to differential conversion in the analog domain, for example using a fully-differential amplifier, etc. They require a differential input signal with common mode voltage of VREF/2, it doesn't work if you tie IN- to ground and treat IN+ as a single-ended input.
      

      The closest fully-differential ADC equivalent to the AD7942 is the AD7687. The AD7687 outputs 16-bit signed data.
      

      Can you explain the nature of the 50Hz wave you're measuring? Is it unipolar or bipolar? What is the amplitude?
      

      Also, why does the data coming out of the ADC need to be signed?
      

      Thanks,
      

      Tyler
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

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