ADL5523ACPZ-R7 datasheet(20/24 Pages) AD

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ADL5523

Data Sheet

Rev. B | Page 20 of 24

S11 OF THE LNA WITH S22 MATCHED

To determine the correct matching circuit for optimal noise,

look at the results of S11 for the various frequencies at which

S22 was tuned earlier in the Tuning S22 section. Once S11 is

determined for a particular frequency, find the matching

components that provided that match. Figure 63 and Figure 64

show S11 for the various frequencies. Again, these measurements

are all based on S22 being matched at that particular frequency.

Note that, for the examples shown in Figure 63 and Figure 64, S11

is either in the lower left quadrant of the Smith Chart or slightly

into the upper left. To move the impedance in the given noise

circle, a series L component at the LNA input is required. The L

values in the examples differ but a correct L value moves the match

along the constant R circle up into the upper left quadrant of the

Smith Chart.

A shunt capacitor can then be added to move the match along a

constant admittance line, down and to the right, directly into

the center of the noise circle given in Figure 61.

The solution for the structure of the match for the examples in

Figure 63 and Figure 64 is a series L to the input of the LNA

and a shunt capacitor at the generator end of this inductor. The

recommended components for matching at various frequencies

are shown in Table 7.

An example of the effect of the series L, shunt C match, based

on the 800 MHz example, is given in Figure 62. This example

uses the output from the Agilent ADS Smith Chart tool.

Figure 62. Example of Series L, Shunt C Matching Network for ΓOPT

FREQUENCY (400MHz TO 4GHz)

FREQUENCY 400MHz

S11 = 0.877/–44.639

IMPEDANCE = Z0 × (0.443 – j2.365)

FREQUENCY 2GHz

S11 = 0.615/–170.569

IMPEDANCE = Z0 × (0.240 – j0.078)

Figure 63. S11 of ADL5523 with S22 Matched at 2 GHz

FREQUENCY (400MHz TO 4GHz)

FREQUENCY 400MHz

S11 = 0.864/–40.186

IMPEDANCE = Z0 × (0.594 – j2.615)

FREQUENCY 3.2GHz

S11 = 0.595/163.164

IMPEDANCE = Z0 × (0.259 + j0.138)

Figure 64. S11 of ADL5523 with S22 Matched at 3.2 GHz

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