ADL5521ACPZ-R7 datasheet(38/45 Pages) AD

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ADL5521

Preliminary Technical Data

Rev. PrC| Page 38 of 45

Figure 126. Area of Optimal Noise Matching for ADL5521, 23

S11 Parameters of ADL5521,23 with S22 Matched

To determine the correct matching circuit for optimal noise, the

next step is to look at the results of S11 for the various frequencies

at which S22 was tuned earlier in this note. Once the S11 is

determined for a particular frequency, all that needs to be done is

to find the matching components that provide that match.

Figure 127 to Figure 132 show S11 for the various frequencies.

Again, these measurements are all based on S22 being matched at

that particular frequency.

Note that the S11 for every example shown in Figure 127 to Figure

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

slightly into the upper left. To move this impedance in the given

noise circle first requires a series L component at the LNA input.

The values for L in all of the examples will differ, but a correct

value of L will move the match along the constant R circle up into

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, hopefully right

into the center of the noise circle given in Figure 126.

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

in Figure 127 to Figure 132 is a series L to the input of the LNA,

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

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

the 800MHz example, is given in Figure 133. This example uses

the output from the Agilent ADS Smith Chart tool.

Frequency

500MHz

82pf

1nf

9nH

12nH

750MHz

2.0pf

11nH

3.4nH

900 MHz

2.4pF

8.2nH

3.4nH

1400 MHz

2.4pF

5.1nH

1950 MHz

1.3pF

1nF

1.1nH

2150 MHz

1.3pf

1.1nH

2400 MHz

1.3pf

1.3nH

Table 8. L and C Values for ADL5521 Matching Circuits at Various Frequencies

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