RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 288
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 8.12. Gain and NF Circles for the BGB707 MMIC at 3 V and 6 mA.
Figure 8.13. Gain and NF for the BGB707 MMIC at 3 V and 6 mA.
The most power can be transmitted using 50 Ω transmission lines, but 75 Ω transmission
lines have the lowest loss, so that 75 Ω impedance levels are used for many receiver
antennae and front-end amplifiers. Figure 8.13 shows a comparison of the gain and noise
performance of the BGB707 MMIC for 75 Ω and 50 Ω terminations at both the input and
output. It can be seen that the 75 Ω terminations give a higher gain and a lower NF.
However, for frequencies below 40 MHz, the Smith chart centre is inside the unstable
regions of the input stability circles, so the amplifier is less stable than the one using 50 Ω
terminations. Later in this chapter, techniques to improve the stability are described.
RF Electronics: Design and Simulation
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