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RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 291 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. that the amplifier is conditionally stable at 12.525 GHz for both the input and output stability circles. This shows that it is important to measure an amplifier's stability outside the normal 50 MHz to 6 GHz operating frequency region, since an amplifier may oscillate at a frequency outside the normal operating range. If an amplifier exhibits less gain or output power capability than expected, or it runs hotter than expected, then it is a good idea to use a spectrum analyser to check if it is oscillating outside the normal frequency region. The PMA5453 is much more stable than the BGB707 but it requires a supply current of 40 to 60 mA, compared to 6 mA for the BGB707. Example 8.3: Bipolar Transistor The interaction between stability factors, noise factors and gain are illustrated using the design of a low noise amplifier using a Infineon BFP540 [11] low noise silicon NPN transistor. The typical specifications of that transistor are: NF = 0.9 dB, at I C = 5 mA, V ce = 2 V, f = 1.8 GHz. Gain = 21.5 dB and OIP3 =24.5 dBm at I C = 20 mA, V ce = 2 V, f = 1.8 GHz. The models for the BFP540 transistor are available from the Elements Libraries * AWR web site Parts by Vendor Infineon. The linear model, is available at Data RF Bipolar Transistors Low Noise Si Transistors up to 5 GHz BFP540. The nonlinear Spice model is at Nonlinear RF Bipolar Transistors Low Noise Si Transistors up to 5 GHz BFP540. In the first example, the linear model, based on S parameters is used. In this example, the Spice based model is used. There are different versions of the BFP540 family. The BFP540 has a slightly lower NF than the BFP540FESD. However, the BFP540FESD has ESD protection, which will protect the transistor from Electro Static Charges, which could be induced on the input. When importing the model into a circuit schematic, a four terminal block is used. That can be changed to a dual emitter transistor symbol. However, that requires the pin numbers in the Spice files to be changed slightly as follows: Original: DEF4P 2 1 3 4 "BFP540FESD" Changed to: DEF4P 1 2 3 4 "BFP540FESD" Figure 8.18. NF versus collector current at 1.8 GHz [Figure 14 of 11]. The NF will vary with frequency and collector current. At < 1MHz the noise rises due to 1/f noise at a rate of 20 dB per decade. This 1/f noise is not normally included in the model for the transistor, since external components such as coupling capacitors are likely RF Electronics: Design and Simulation 291 www.cadence.com/go/awr

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