5.3 Impedance Matching

Chapter 5.3 Impedance Matching

Radio Frequency Integrated Circuit Design Second Edition Book
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Radio Frequency Integrated Circuit Design Second Edition Book

  • 106 Impedance MatchingAnother value that is often calculated related to the reflection coefficient is called the return loss (RL) and it is given by: 1120 log20 log1VSWRRLVSWRæ ö+æö==ç÷ç ÷èø-Gè ø (5.6)Note if the system is perfectly matched, the RL is minus infinity and the VSWR would be one.5.3  Impedance MatchingThe input impedance of a circuit can be any value. In order to have the best power transfer into the circuit, it is necessary to match this impedance to the impedance of Figure 5.8  The eight possible impedance matching networks with two reactive components.Table 5.2  Using Lumped Components to Match Circuits Component AddedEffectDescription of EffectSeries inductorz ® z + jwLMove clockwise along a resistance circle. Series capacitorz ® z - j/wCSmaller capacitance increases impedance (-j/wC) to move counterclockwise along a resistance circle. Parallel inductory ® y - j/wLSmaller inductance increases admittance (-j/wL) to move counterclockwise along a conductance circle.Parallel capacitory ® y + jwCMove clockwise along a conductance circle.