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## ADL5523 Datasheet(HTML) 20 Page - Analog Devices

 20 / 21 page ADL5523Data SheetRev. C | Page 20 of 21S11 OF THE LNA WITH S22 MATCHEDTo determine the correct matching circuit for optimal noise,look at the results of S11 for the various frequencies at whichS22 was tuned earlier in the Tuning S22 section. Once S11 isdetermined for a particular frequency, find the matchingcomponents that provided that match. Figure 63 and Figure 64show S11 for the various frequencies. Again, these measurementsare all based on S22 being matched at that particular frequency.Note that, for the examples shown in Figure 63 and Figure 64, S11is either in the lower left quadrant of the Smith Chart or slightlyinto the upper left. To move the impedance in the given noisecircle, a series L component at the LNA input is required. The Lvalues in the examples differ but a correct L value moves the matchalong the constant R circle up into the upper left quadrant of theSmith Chart.A shunt capacitor can then be added to move the match along aconstant admittance line, down and to the right, directly intothe center of the noise circle given in Figure 61.The solution for the structure of the match for the examples inFigure 63 and Figure 64 is a series L to the input of the LNAand a shunt capacitor at the generator end of this inductor. Therecommended components for matching at various frequenciesare shown in Table 7.An example of the effect of the series L, shunt C match, basedon the 800 MHz example, is given in Figure 62. This exampleuses the output from the Agilent ADS Smith Chart tool.Figure 62. Example of Series L, Shunt C Matching Network for ΓOPTM2M1FREQUENCY (400MHz TO 4GHz)M1FREQUENCY 400MHzS11 = 0.877/–44.639IMPEDANCE = Z0 × (0.443 – j2.365)M2FREQUENCY 2GHzS11 = 0.615/–170.569IMPEDANCE = Z0 × (0.240 – j0.078)Figure 63. S11 of ADL5523 with S22 Matched at 2 GHzM2M1FREQUENCY (400MHz TO 4GHz)M1FREQUENCY 400MHzS11 = 0.864/–40.186IMPEDANCE = Z0 × (0.594 – j2.615)M2FREQUENCY 3.2GHzS11 = 0.595/163.164IMPEDANCE = Z0 × (0.259 + j0.138)Figure 64. S11 of ADL5523 with S22 Matched at 3.2 GHz