• State Verified Answer
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 66 subscribers
  • Views 392 views
  • Users 0 members are here
Options
Related 

        

            Post
             Go back to editing
        

    

    


    

    









		











	
	
			
	
			
		
	
	
		

		
Connecting High speed DAC to Mixers in Digital modulation scheme



		

			

									
						veera
					
							

			
				
									
											
							 		
		        	            							
			
			    	
			                    
                
				                on Aug 25, 2012 
				
			
			
		


				
		

		    		    
		    
		    	
			
Hi,

 
In digital IQ modulation based systems, the High speed DACs are connected directly to mixers by skipping IQ modulators.

 
In this case can we use same circuitry (which are used in connecting DACs to Modulators) to connect DACs to Mixers (Passive reconstruction filter circuit) or should we add any additional circuitry. Will the DAC seamlessly connect to the Mixer or should we do any power conversion with VGA or step attenuators.

 
The DAC used - AD9746

 
Mixer - ADL5801.

 
(DAC o/p frequency - 30 MHz)

 
Thanks in advance

								


				
				
		

			
						
									
									
						
						
			
			
			
			
		


					

			





	










	

	

					



			








	
	
	
	



Parents
	
    
	

  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
			
													0
							
			
				
									
							        
            
                                                                                                        
      
                            
    • 
                                 Analog Employees 
                                
                            
      • 
                        
     
                                                           			
			                            
                        
                on Aug 28, 2012 12:24 AM
            
            
					
    
	
    

		
		
    
					
    In a typical signal chain which you describe, in which the DAC drives a mixer (not an IQMod)  the baseband I and Q channels must be modulated onto the carrier at low IF either in the DAC, or in the digital engine previous to the DAC. Since the AD9746 does not have any IQModulation capability (we have other DACs that do this, AD9122 and AD9788 as examples) I'm assuming that you must be doing the IQMod in the digital domain previous to the DAC. Can you confirm? If this is true, I'm curious why you are choosing a dual DAC like the AD9746 to drive a mixer, what is the other DAC channel doing? Also, since the AD9746 can only generate somewhat low IF frequencies, I think you are going to have to deal with the undesired sideband at LO-IF, where if you used the analog IQMod approach after the dual DAC, this image would be supressed by at least 40dB with no compensation. Please let me know if I am misunderstanding anything
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

    • 

	




Reply

    


  • 
	
    



	
		
	
	



    
	
    
		
    
							
					
    
		
    
			
													0
							
			
				
									
							        
            
                                                                                                        
      
                            
    • 
                                 Analog Employees 
                                
                            
      • 
                        
     
                                                           			
			                            
                        
                on Aug 28, 2012 12:24 AM
            
            
					
    
	
    

		
		
    
					
    In a typical signal chain which you describe, in which the DAC drives a mixer (not an IQMod)  the baseband I and Q channels must be modulated onto the carrier at low IF either in the DAC, or in the digital engine previous to the DAC. Since the AD9746 does not have any IQModulation capability (we have other DACs that do this, AD9122 and AD9788 as examples) I'm assuming that you must be doing the IQMod in the digital domain previous to the DAC. Can you confirm? If this is true, I'm curious why you are choosing a dual DAC like the AD9746 to drive a mixer, what is the other DAC channel doing? Also, since the AD9746 can only generate somewhat low IF frequencies, I think you are going to have to deal with the undesired sideband at LO-IF, where if you used the analog IQMod approach after the dual DAC, this image would be supressed by at least 40dB with no compensation. Please let me know if I am misunderstanding anything
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
						
				
						
				
				
		
		
    
			
		
    
	
    

    

    • 





Children
	
No Data