Products In This Thread

AD7983 Production
The AD7983 is a 16-bit, successive approximation, analog-to-digital converter (ADC) that operates from a single power supply, VDD. It contains a low power...
Datasheet
AD7983 on Analog.com

  • State Verified Answer
  • Replies 2 replies
  • Subscribers 70 subscribers
  • Views 1242 views
  • Users 0 members are here
Options
Related 

        

            Post
             Go back to editing
        

    

    


    

    









		












	
	
			
	
			
		
	
	
		

		
AD7983 input driven by multiplex signals



		

			

									
					    jake65892
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Oct 18, 2011 
				
			
			
		
    

				
		
    
		    		    
		    
		    	
			
    I want to drive the AD7983 with a multiplexed signal.  I am having a hard time understanding the best time to switch the multiplexor based on the timing diagram in the datasheet.
    
 
    I would like to switch the multiplexor as soon as possible after the rising edge of the CNV pulse in order to maximize the settling time of the next signal's driving circuitry.  So, I would raise the CNV, wait for the converter to "do its thing", and then switch the mux.  How long must I wait for the converter to "do its thing" before I change the input, without degradation of the conversion.
    
 
    Looking at the datasheet, I cannot tell if this time is t_CNVH, t_CONV, or some other time.  If it is in fact t_CONV, what causes the 300 to 500 ns span?  And which should I use, 300 or 500?
    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			


				
	









	
      
	

    • 
	
      



	
		
	
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Oct 18, 2011 3:53 PM
            
            
					
      
	
      

		
		
      
					
      Hello Jake,
      
 
      Thanks for your question. 
      
 
      Once the converter has received the rising edge of CNV, the ADC internal switch will open and the device will then be in hold mode and start converting.Therefore, shortly after the rising edge of the CNV signal, you'll be able to switch your mux channel.wait at least the 10ns, but after that you can safely switch. 
      
 
      Where is the multiplexer in the signal chain? 
      
 
      Will you use an ADC driver amplifier between the mux and the ADC input? This would the preferred approach. What amplifier will you use? The amplifier will need the performance noted in the ADC datasheet, but will now also need to be capable of potentially settling a full scale step within the cycle time of the conversion/acquisition (750ns), be mindful of this when you select the driver/amplifier. The ADA4841-1 is one amplifer that should be capable of this. 
      
 
      Please let me know if you need further advice here or have additional questions. 
      
 
      Best regards,
      
 
      Catherine. 
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

      • 

	

    • 
	
      



	
			
		
	



      
	
      
		
      
							
					
      
		
      
			
													0
							
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
			                            
                        
                on Aug 2, 2018 5:27 PM
            
            
					
      
	
      

		
		
      
					
      This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

      Thank you,
      EZ Admin
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
						
				
				
		
		
      
			
		
      
	
      

      

      •