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Changing x-value of a signal and/or handle signals with multiple outputs

itos

Hello,

My question from https://community.cadence.com/cadence_technology_forums/f/custom-ic-design/38589/image-rejection-of-iq-mixer is still up :( So far I found the following hack: PSS+PAC, relative harmonic=1 and frequency sweep -100M ... 100M (for example). Then:

leafValue(v("/vodi" ?result "pac") "harmonic" -1) + (sqrt(-1) * leafValue(v("/vodq" ?result "pac") "harmonic" -1))

Similarly as combining the I/Q data in time domain I add them in frequency domain (pac data) as complex value. The problem is that this maps both the positive and negative frequencies to the same (positive) frequency values.

Question 1: When I plot this (or export to CSV/Table) one x value (e.g. 10 MHz) has 2 y values (one for positive and one for the negative frequency). How do I obtain the individual values? If I use value it just gives me the mean!

Question 2: Is there any way to modify the x-value of the pac data to include negative frequencies?

Thanks!

  • Andrew Beckett

    Quick answer - which may solve both questions (I don't have time post-vacation to do an experiment to check what you're saying as I have a lot of catching up to do!). On the pac options form, set the freqaxis parameter to "out" (rather than the default "absout"). Then you should get the negative frequencies in the data.

    Regards,

    Andrew.

  • itos
    in reply to Andrew Beckett

    I guess you mean "Sweeptype"? I tried that already ... no change between Relative/Absolute.

    However, I came up with a different solution now:

    value(dB20((mag((leafValue(v("/vodi" ?result "pac") "harmonic" -1) + (sqrt(-1) * leafValue(v("/vodq" ?result "pac") "harmonic" -1)))) / mag((leafValue(v("/vodi" ?result "pac") "harmonic" -1) - (sqrt(-1) * leafValue(v("/vodq" ?result "pac") "harmonic" -1)))))) 100000)
    

    Basically this gets two expressions:
    

    1.) OUT_I + 1j*OUT_Q
    

    2.) OUT_I - 1j*OUT_Q
    

    They represent the two sidebands and their ratio is the image rejection, as used in the formula above. (I hope - but the results look reasonable).
    

    

    

    

    

    

    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
				
				
				
				
		
		
    
			
		
    
	
    

    


    

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												Andrew Beckett
									
    
		
    
			
											
			
				
									
							
						
				
			
												
						in reply to itos
					
									
    
	
    

		
		
    
					
    No, I mean "freqaxis" on the PAC options form; not "sweep type" on the main PAC form:
    

     
    
			
    

		
		
		
		
	
    
	
    
		
    
			
		
    
	
    
	
    
		
						
				
				
				
				
				
		
		
    
			
		
    
	
    

    


    

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