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Input matching of switched capacitor ADC (AN-742)

Question asked by 6j5 on Jul 20, 2011
Latest reply on Jul 22, 2011 by RReeder

Application Note AN-742

 

One page  4 of AN-742 the design example uses AD9236 input impedance values taken from a graph Fig.6 on page 3 (or tabulated S parameter data) and it appears to be interpretted as elements of a parallel equivalent circuit.

 

However AN-827 which elaborates on the method and displays exactly the same graphs states that the R &C elements in the plots are SERIES equivalents and gives a method to convert to the parallel equivalent circuit better suited for matching circuit design.

 

So although the general design outline in AN-742 is sound, the parameter values used  appear to me to be inconsistent with the interpretaion given in AN-827.

 

Any comment on this greatly appreciated.

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