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AD8362 Production
The AD8362 is a true rms-responding power detector that has a 65 dB measurement range. It is intended for use in a variety of high frequency communication...
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AD8362 on Analog.com

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AD8362 residual noise, ADC oversampling

		
	
				

			

									
					    rianovich96
					
							

            
            			
				
									
											
			
			
				
			
			
			    	
			                    
                
				                on Mar 14, 2013 
				
			
			
		

		
		                    	    

        	    
Thread Summary

                The user inquired about using the AD8362's output with a 10-bit ADC and oversampling to achieve 14-bit ENOB resolution. The intrinsic circuit noise after an RC LPF was questioned for its suitability as white noise. The final answer noted that the question was considered resolved, either offline or through a multi-part response. Accompanying answers clarified that for unmodulated carriers, the residual output noise is broadband white noise, but for modulated carriers, the noise is not white and may require additional filtering. The AD8362's transfer function ripple and temperature drift were also highlighted as potential limitations, suggesting the ADL5902 as a more stable alternative.
                        	    

                
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I plan to acquire AD8362's output with some 10bit ADC and using oversampling & decimation for 14bit ENOB resolution. The question is that the intrinsic circuit's noise (after some hardware RC LPF) would be suitable as "white noise", uncorrelated, in order to benefit the oversampling technique.

 
Thanks very much in advance for clarifications,

			

			
									
		                             
                        

    

                                            
                 ad8362
                
                                                    
                 RF Power Detectors
                
                                                    
                 Logarithmic RMS Detectors
                
                                                    
                 rf and microwave
                
                                
            

    
    
		


				
				        
        		

			
						
									
												
			
			
                        
                                    
                        
                                                    
                        
            
			            
						
						
			
			
			
			
		


        
        
        
    
					

			





















	

	

					



			








	
	
	
	



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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Mar 14, 2013 1:38 PM
            
            
						
			            		
    
		
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    If you are measuring the power of a modulated carrier (e.g. QPSK, QAM64, FM, etc) then the spectrum of the carrier will effectively mix down to dc and will manifest itself as noise which has to be filtered. I'm not sure that you can consider this to be white noise.
    
 
    If you are measuring the power of an unmodulated carrier, then I think that it's fair to say that your residual output noise is broadband white noise.
    
 
    I'm not sure of the value of the filtering you are planning on doing. If you look at the Vout vs Pin transfer function of the AD8362, you can see that there is transfer function ripple and nonlinearitt that is of the order of 0.5 dB or about 30 mV. Also the device has temperature drift of the order of +/-1 dB (approx +/-60mV).  So unless you plan to operate over a very narrow temperature range and plan to calibrated out the transfer function ripple, I'm not sure that filtering for 14 bit resolution has value.
    
 
    Finally, ADL5902 is a newer better part than AD8362. Its temperature stability and transfer function ripple are much smaller than AD8362. 
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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    •  Analog Employees  
    
            
						
                            
            
            				
            
                on Mar 14, 2013 1:38 PM
            
            
						
			            		
    
		
										0
					
	
    

		
		
    
		
    
                                
                                                            
    
					
    If you are measuring the power of a modulated carrier (e.g. QPSK, QAM64, FM, etc) then the spectrum of the carrier will effectively mix down to dc and will manifest itself as noise which has to be filtered. I'm not sure that you can consider this to be white noise.
    
 
    If you are measuring the power of an unmodulated carrier, then I think that it's fair to say that your residual output noise is broadband white noise.
    
 
    I'm not sure of the value of the filtering you are planning on doing. If you look at the Vout vs Pin transfer function of the AD8362, you can see that there is transfer function ripple and nonlinearitt that is of the order of 0.5 dB or about 30 mV. Also the device has temperature drift of the order of +/-1 dB (approx +/-60mV).  So unless you plan to operate over a very narrow temperature range and plan to calibrated out the transfer function ripple, I'm not sure that filtering for 14 bit resolution has value.
    
 
    Finally, ADL5902 is a newer better part than AD8362. Its temperature stability and transfer function ripple are much smaller than AD8362. 
    
			
    

		
			
	      

		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
				
				
				
		
		
    
			
		
    
	
    

    

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