Products Mentioned

AD8302 Recommended for New Designs
The AD8302 is a fully integrated system for measuring gain/loss and phase in numerous receive, transmit, and instrumentation applications. It requires...
Datasheet
AD8302 on Analog.com

Thread Details

  • State Verified Answer
  • Replies 1 reply
  • Subscribers 70 subscribers
  • Views 110 views
  • Users 0 members are here
 
Related Content

        

            Post
             Go back to editing
        

    

    


    

    









		


















	
	
			
	
			
		
	
	
		

	    
	    
	    		
slope  error in voltage vs phase angle plot

		
	
				

			

									
					    RCarl
					
							

            
            			
				
									
											
			
			
				
    
			
			
			    	
			                    
                
				                on Jan 14, 2026 
				
			
			
		
    
		
		                    	    
    
        	    
    Thread Summary
    
                The user is experiencing a small slope offset when using the AD 8302 to detect phase differences at 225 kHz. The final answer suggests fine-tuning the slope using resistors between VPHS and PSET, or calibrating the VPHS output in software by applying known phases and measuring the corresponding voltages to calculate and store the slope and intercept for each device.
                        	    
    
                
                     AI Generated Content
                
    	    
    
             
				
        		
    
		    
		    		    
    
		      		            		        
    Category: Hardware
    
    		        		            		    
    Product Number:  AD8302  
    
    		        		    		    
    
		    		    
		    			
    
			    
    I am using a AD 8302 to detect the phase difference between two voltage signals.  The frequency is 225 kHz.   I used the application notes on the topics  of the AD 8302  to pick relevant input high pass filter and Cflt capacitors.
    

    No mater what values of input and Cflt values I try,  however,   I get a small slope  offset like in the graph shown here.  My circuit is here. 
    

    Based on the data sheets, it  seams like I should not have to mess with the R110 (presently shunted) and  R111(presently open)  if I just want 1.8volts per 180 degrees.
    
			
    
			
									
		                             
                        

    
    
                                            
                 hardware
                
                                                    
                 Vector Power Measurement
                
                                                    
                 RF Power Detectors
                
                                                    
                 ad8302
                
                                
            
    
    
    
		
    

				
				        
        		
    
			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		
    

        
        
        
    
					
    
			
    


    
















    
	
    
	
    
					



			


				
	









	
      
	

    • 
	
      



	
			
		
	



      
	
      
		
      
							
					
      
		
      
		    
		    		    
			
				
									
							        
			
			
			
      •  Analog Employees  
      
            
						
                            
            
            				
            
                on Jan 15, 2026 10:46 AM
            
            
						
			            		
      
		
										0
					
	
      

		
		
      
		
      
                                
                                                            
      
					
      While the datasheet specifies typical slopes for the VPHS phase output (e.g. 10mV/deg at 100 mHZ), the slope will vary on a device-to-device basis. So the device is not going to give you absolute accuracy. You have two options.
      1. Use the resistors between VPHS and PSET to fine tune the slope.  That will require that one of those resistors will be a potentiometer or a digipot. Also, in production, you will have to individually adjust each system.
      2. If you plan to digitize the VPHS output, you could calibrate in software. So, you would apply two known phases (say 30 deg and 150 deg), measure the corresponding VPHS voltages (or ADC codes) and back calculate the slope and intercept for that particular device. Once the slope and intercept ADC codes are calculated and stored, you can use them to calculate phase when the system is operational. 
         
        Best Regards
         
        Eamon
          
      
			
      

		
			
	      

		
		
	
      
	
      
		
      
			
		
      
	
      
	
      
		
						
				
						
				
				
				
		
		
      
			
		
      
	
      

      

      •