AWR eBooks

RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 307 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. In the designs presented here, the equations for the matching networks are evaluated inside Cadence AWR DE. This allows design parameters to be changed or optimised and allows the effect of such design parameters changes to be observed. Pi Network The Pi matching network is very useful for matching high impedance sources to 50 loads. Pi matching is normally used in valve, or tube, amplifiers. For high power solid- state devices, the impedance values become impractical with very large capacitors and very small inductors being required. Figure 9.1 shows the Pi network used for matching. To obtain the component values, firstly decide on a Q value for the matching network. The Q value will affect the bandwidth, harmonic attenuation and component stress. For the Pi network, the input impedance needs to be a parallel network, so that a series to parallel transformation may need to be applied before the network evaluation as shown in equation 9.3, which transforms the device impedance of RD+jXD into RP in parallel with XP. The equations for the Pi network in AN267 assume that the device is resistive and that any reactive impedances are compensated for after the Pi network is designed. Figure 9.1. Pi matching network. The equations in the included MWO files handle reactive parts correctly. The complete equations for the Pi matching network are as follows: D D D p R X R R 2 2 D D D p X X R X 2 2 Eqn. 9.3 P P C C X R Q X Y 1 1 1 1 Eqn. 9.4 L P L P L C R R Q R R R X ) 1 ( 2 2 Eqn. 9.5 1 ) ( 2 2 Q X R R QR X C L P P L Eqn. 9.6 Note that Q 2 +1 must be larger than R P /R L for X C2 to be valid, so that there is a minimum Q value for a given impedance transformation ratio. RF Electronics: Design and Simulation 307 www.cadence.com/go/awr

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