ADL5523_09 AD [Analog Devices], ADL5523_09 Datasheet - Page 20

• Manufacturer Part Number: ADL5523_09
• Description: 400 MHz to 4000 MHz Low Noise Amplifier
• Manufacturer: AD [Analog Devices]

ADL5523
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 62 and Figure 63
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 62 and Figure 63, 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 60.
The solution for the structure of the match for the examples in
Figure 62 and Figure 63 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 61. This example
uses the output from the Agilent ADS Smith Chart tool.
Figure 61. Example of Series L, Shunt C Matching Network for Γ
OPT
Rev. A | Page 20 of 24
Figure 63. S11 of ADL5523 with S22 Matched at 3.2 GHz
Figure 62. S11 of ADL5523 with S22 Matched at 2 GHz
M2
M2
FREQUENCY (400MHz TO 4GHz)
FREQUENCY (400MHz TO 4GHz)
M1
FREQUENCY 400MHz
S11 = 0.877/–44.639
IMPEDANCE = Z0 × (0.443 – j2.365)
M2
FREQUENCY 2GHz
S11 = 0.615/–170.569
IMPEDANCE = Z0 × (0.240 – j0.078)
M1
FREQUENCY 400MHz
S11 = 0.864/–40.186
IMPEDANCE = Z0 × (0.594 – j2.615)
M2
FREQUENCY 3.2GHz
S11 = 0.595/163.164
IMPEDANCE = Z0 × (0.259 + j0.138)
M1
M1