RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 293
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 8.21 shows a plot of K, B and Input and Output stability factors. For
unconditional stability K>1, MU1>1 and MU2>1 and B>0. It can be seen that in the
region of 3.5 MHz to 3 GHz, the amplifier is only conditionally stable. The amplifier is
stable with a 50 source and load impedance as shown in the gain plot of figure 8.20.
Figure 8.22 shows the input and output stability circles plotted at 1 GHz, confirming that
the BFP540 amplifier is only conditionally stable, but is stable for an input and output
VSWR better than 2.5:1. The corresponding BFP540FESD (Electro-Static Protected)
amplifier is stable for an input and output VSWR better than 3:1. However, the
BFP540FESD has a 0.15 dB worse NF. To investigate the difference in performance
between the BFP540 and the BFP540FESD simply change the linked netlist in the Circuit
Schematics in the Ch8-Fig 19-24 AWR DE project file accompanying this book. The
Input Stability Circle is shown in blue and the Output Stability Circle is shown in red.
Figure 8.21. Stability factors for the basic amplifier.
Figure 8.22. Stability input and output circles at 1GHz.
RF Electronics: Design and Simulation
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