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RF Electronics Chapter 9: Impedance Matching of Power Amplifiers Page 338 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 9.58 shows that the amplifier is also stable over the entire 10 MHz to 2 GHz frequency range. To achieve this stability, shunt resistors Rin2 needed to be added to the input matching network, as shown in figure 9.53. Figure 9.59. CGH40090PP-AMP demonstration amplifier [9]. Figure 9.59 shows the CGH40090PP-AMP demonstration amplifier, available from Wolfspeed. That amplifier has a PAE of typically 50% and an output of 50 dBm over a 0.5 GHz to 2.5 GHz bandwidth with a gain that varies between 12 and 18 dB. The circuit for this is more complex than the one shown in figures 9.46 and 9.53. The "Innovative Power Products" hybrids perform the same function as the coaxial Balun shown in figures 9.53 and 4.55. Notice how the low transmission-line impedances for the output matching result in very wide PCB tracks. The pads along the output transmission lines allow the tracks to be widened, or shunt capacitors to be placed to fine-tune the amplifier's performance. Black SMD components near the gate of the FET is a resistor, required for stability. In the CREE design that resistor has a capacitor in parallel with it to improve the high frequency performance. FET's in general, have better linearity than bipolar transistors and are thus preferred for applications requiring a low intermodulation distortion, such as mobile radio base-station amplifiers or DAB and TV transmitters. FET's have very high gains at low frequencies and are thus more susceptible to instability. Most commercial VHF and UHF high power transmitters [6, 7] use Doherty amplifiers. These [11, 12] consist of a main amplifier that provides the average power and a peaking amplifier that provides the peak power levels. The design of Doherty amplifiers is beyond the scope of this book. David Vye [13] provides an excellent design tutorial on the design of a Doherty power amplifier using advanced transistor models. Having an accurate non-linear model of the FET, allows the performance of the amplifier to be simulated accurately, thus reducing the number of iterations of a PCB that is required for producing a good RF power amplifier. The Cadence AWR FAQ web site has useful additional information about Power Amplifier Design Flow [14], which covers information that is outside the scope of this book, but can assist the design of RF power amplifiers. RF Electronics: Design and Simulation 338 www.cadence.com/go/awr

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