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RX impedance match question.

Question asked by alanr on Sep 12, 2014
Latest reply on Sep 12, 2014 by tlili

I'm having trouble with matching to the RX1A input port.  Right now I'm specifically looking at low frequencies, trying to match from the 70 MHz lower limit up to about 1GHz.  Unfortunately, I don't have the best software to fully simulate my board and components, but I expected to get close.  I am using a 4:1 impedance transforming balun based upon the impedances published in the AD9361 RFPortInterface_v2.1 document, along with some other matching elements such as inductance to cancel some of the capacitive reactance shown.  Also, I'm using AD936X_RX1A_RX2A_MG_DM_SEDZ_Release_1_120424.s1p in the simulation software that I do have, which seems to recreate the Smith chart on page 5 of the pdf. I noticed in the document that it said to conatcy App Engineering for the latest impedance values and that you needed to specify the RX Gain. The s-parameter file says that the data was taken with maximum RX gain, so I presume that the data plotted in the pdf file is also with maximum gain.  When I turn the gain down my match improves considerably.  Is there any data available that presents the s-parameters as a function of the gain setting?  This may give me a clue as to why my match works better at lower gains.