RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 294
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 8.23 shows the input and output stability circles over a 10 MHz to 10 GHz sweep,
and includes VSWR circles for VSRW ratios of 1.3:1, 1.5:1 and 2:1. For an
unconditionally stable amplifier, the entire inside of the Smith Chart will be clear of any
stability circles. From the input stability circles, the amplifier with 50 Ω termination is
stable if the input has a VSWR less than 1.3. By disabling the SCIR1 (input) stability
circle measurements, the output stability circles can clearly be seen and from them the
amplifier is stable if the output has a VSWR less than 2:1.
Figure 8.23. Stability input and output circles over 10MHz -10 GHz.
Figure 8.24. Constant gain and NF circles at 1 GHz.
Figure 8.24 shows the amplifier's constant gain and NF circles. Matching the amplifier
input impedance to the centre of the constant noise circles, results in the lowest NF.
Matching the input impedance of the amplifier to the centre of the available gain
RF Electronics: Design and Simulation
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