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266 Linear Amplilier <strong>Design</strong> Tools<br />

circle is shown along with r ML and r M " according to (E.13) and (E.12). Any<br />

load may be selected on the lO-dB circle. Choose the one nearest the center; it<br />

is 0.567 /33.85°. Usually, it is the lO-dB transducer gain locus that is desired;<br />

therefore, the source must be the conjugate <strong>of</strong> the input reflection coefficient.<br />

From (7.32), the input reflection coefficient for the selected load is<br />

0.276 (-93.33°. The source reflection must be the conjugate <strong>of</strong> this value,<br />

and it is obtained by impedance matching, as discussed in Chapter Six. It is<br />

also plotted in Figure 7.20.<br />

Example 7.11. Use the scattering data from (7.106) for the conditionally<br />

stable device considered in stability Example 7.9. Plot the l2-dB gain circle.<br />

The maximum 50-ohm transducer gain is &=7.290 by (E. 14). Therefore, since<br />

12 dB corresponds to 15.849, g2= 15.849/7.290=2.174. Then (7.115) locates<br />

+1<br />

/ Input stability circle<br />

X=' +0.5<br />

+2<br />

Output<br />

stability<br />

circle<br />

I~<br />

" e<br />

X'" -0.5<br />

-2<br />

-1<br />

1.0 0.8<br />

I<br />

I<br />

0.6 0.4 0.2 0.0 0.2 0.4 0.6<br />

Figure 7.21. Smith chart for Example 7.11,<br />

0.8 1.0

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