Radio Frequency Integrated Circuit Design - Webs

72 Radio Frequency Integrated Circuit Design
Figure 4.10 Matching process.
Solution
Using the techniques above, two matching circuits as shown in Figure 4.11 are
designed. The frequency response can be determined with the results shown in
Figure 4.12. It would seem from this diagram that for the lowpass matching
network, the signal can be transferred from dc to the −3-dB corner at about
1.53 GHz. However, as seen in the plot of the input impedance in Figure 4.13,
the impedance is only matched in a finite band around the center frequency.
For the lowpass network, the impedance error is less than 25� from 0.78 to
1.57 GHz. It can be noted that if the mismatch between the source and the
load is increased, the bandwidth of the matching circuit will be narrower.
For optimal power transfer and minimal noise, impedance should be
controlled (although the required impedance for optimal power transfer may
not be the value for minimal noise). Also, sources, loads, and connecting cables
or transmission lines will be at some specified impedance, typically 50�.