RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 302
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 8.36 shows the stability circles of the amplifier of figure 8.34. Figure 8.37 shows
the corresponding stability factors. The worst stability is in the region of 300-500 MHz.
Comparing these figures with figures 8.23 and 8.21, shows that the amplifier stability has
been improved enormously by simply inserting an attenuator at the amplifier output. This
has made a negligible difference in the NF.
Conclusion
This chapter has described factors involved in amplifier stability. It was shown that
selecting the correct input impedance will result in an optimum noise factor, but may
affect amplifier stability. In many cases, the amplifier can be made unconditionally stable
by changing the load applied to the amplifier or placing an attenuator in between the
amplifier and its output terminals.
References
Note: all web addresses were checked in September 2021.
1. Mini-Circuits, ERA-3+, https://www.minicircuits.com/WebStore/dashboard.html?
model=ERA-3%2B
2. Mini-Circuits, PMA-5453+, https://www.minicircuits.com/WebStore/dashboard.
html?model=PMA-5453%2B
3. Smith, P. H. "Transmission Line Calculator", Electronics, Vol. 12, No. 1, pp 29-
31, January 1939.
4. Smith, P. H. "An Improved Transmission Line Calculator", Electronics, Vol. 17,
No. 1, p 130, January 1944
5. D. M. Pozar, "Microwave Engineering" 3rd Edition, Wiley, 2005, Section 4.3 and
Chapter 11. ISBN 0 471 44878 8
6. R. Gilmore, "Practical RF Circuit Design for Modern Wireless Systems", Artech
House, 2003.
7. Ecosorb Microwave absorber. https://www.laird.com/tool-bar?q=eccosorb
8. Harald T Friis Biography http://ethw.org/Harald_T._Friis
9. NORSAT Ku band LNB, http://www.norsat.com/solutions/microwave-products/
lnb-ku-band/
10. Infineon bgb707L7ESD LNA MMIC, https://www.infineon.com/cms/en/product/
rf-wireless-control/low-noise-amplifier-lna-ics/general-purpose-lnas/bgb707l7esd/
11. Infineon BFP540, https://www.infineon.com/cms/en/product/rf-wireless-control/
rf-transistor/low-noise-si-transistors-up-to-5-ghz/bfp540/
12. C. Coleman; An introduction to Radio Frequency Engineering, Cambridge
University Press, 2004. ISBN 0 521 83481 3.
Abbreviations
dBm dB with respect to 1 mW.
E-PHEMT Enhancement-mode Pseudomorphic High Electron Mobility Transistor.
ESD Electro Static Discharge.
G
A
Available Power Gain.
G
T
Transducer Power Gain.
HEMT High Electron Mobility Transistors.
InGaP HBTs Indium Gallium Phosphide Heterojunction Bipolar Transistors.
LNB Low Noise Block downconverter.
RF Electronics: Design and Simulation
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