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AD6676 IDAC_FS calculation and its impact on setting PIN_0DBFS



		

			

									
					    Revanthac123
					
							

			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 20, 2023 
				
			
			
		
    

				
		
    
		    		    
		    
		    		            		        
    Category: Datasheet/Specs
    
    		        		        		    		    	
			
    Hello,
    

    I am working on AD6676 chip ,and I am referring to Wideband IF Receiver Subsystem AD6676 Datasheet.
    

    I have to change the default PIN_0DBFS value to -2.7dBm as per the specification provided for my project.So in order to change that I used the equation (2) & (4) given in pg no - 28 and 29 in the datasheet ,
    

    PIN_0dBFS = 10 × log10(1/2 × RIN × IDAC1FS^2)   ---> (2),
    

    IDAC1FS = 4 mA × (IDAC1_FS/64)            ----> (4),
    

    I have set the following parameters as follows :
    

    FIF  => 258 Mhz,
    

    BW  => 56Mhz,
    

    FADC => 3200Mhz,
    

    Lext => 10nH,
    

    IDAC1FS => 0x40 (0x10A register)
    

    RIN => 60 ohm
    

    Therefore considering all these above parameters ,as per the above equations ,I got PIN_0dBFS value as -3.18759 dBm theoretically.
    

    But when we overwrite the IDAC1FS register(0x10A) ,we are not able to see any changes in the PIN_0dBFS value practically ,Is there anything that I have to take care so that I can see changes in the PIN_0dBFS.
    

    Please do let me what changes needs to be done to obtain my PIN_0dBFS value as -2.7dBm
    

    Also refer to this link as well because it also points to the same issue :  AD6676 PIN_0DBFS calculation  
    

    
								
    

				
				
		
    
			
						
									
									
						
						
			
			
			
			
		
    

        
        

					
    
			
    


    


	
    
		
	
    















    
	
    
	
    
					



			








	
	
	
	



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      •  Analog Employees  
      
            
			                            
                        
                on Jan 20, 2023 8:18 PM
            
            
					
      
	
      

		
		
      
					
      Hello,
      

      Since you PIN_0dBFS for 4 mA measures to be 0.5 below your target of -2.7 dBm,  one can set the RxPGA attenuator to 1 dB (0x181=0x01) thus increasing your PIN_0dBFS from -3.2 dBm to -2.2 dBm and then reduce your IOUTFS by a small amount (set to IOUTFS  register 0x10A=0x3C) to reduce your PIN_0dBFS so that it is -0.5 dB lower thus giving you -2.7 dBm.  

      Once can increment or decrement this register by 1 to see if it gets you closer to target -2.7 dBm. 

      Regards
      
			
      

		
		
		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
						
				
						
				
				
		
		
      
			
		
      
	
      

      

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													0
							
			
				
									
							        
			
			
			
        
            
			                            
                        
                on Jan 23, 2023 3:07 PM
            
            
												
						in reply to PMH
					
									
        
	
        

		
		
        
					
        Thanks for the reply.
        

        But as per the datasheet pg-14 .figure -20 corresponds to -2.7dBm wihout any attenuator changes,it is kept 0 in the configurations.
        

        So is there any other way to increase the PIN_0dBFS value to -2.7dBm without using the attenuator register as suggested above??
        
			
        

		
		
		
		
	
        
	
        
		
        
			
		
        
	
        
	
        
		
						
						
				
						
				
				
		
		
        
			
		
        
	
        

        

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