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RF Electronics Chapter 2: Computer Simulation Page 23 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. The transistor gain, Beta, can be tuned to observe the biasing voltage changes that occur when the value of Beta changes. The Emitter stabilisation provides good stability when Beta changes. Frequency Response of these amplifiers for Beta=200 is shown in fig 2.24. Note that the Emitter Bias Stabilised amplifier has a lower input impedance and thus a higher low frequency corner frequency. Example 2.3: Low Noise Amplifier The non-linear models are now applied to the design and simulation of a low noise amplifier. The design is to use a BFP720 Silicon Germanium Carbon (SiGe:C) NPN Hetero-junction transistor. The SPICE transistor model can be obtained from the AWR Vendor Library from Parts By Type Nonlinear Infineon RF Bipolar Transistors Ultra Low Noise SiGe:C Transistors up to 12 GHz BFR720. Add the part to the schematic. The transistor package has two emitter leads, if desired the transistor symbol can be changed by right clicking on the transistor block and selecting properties. Then select symbol NPN_hbt@APLAC.syf to replace the 4 terminal block with a double emitter transistor symbol, as shown in figure 2.25. If desired, instead of using Web access to insert the transistor model, the Vendor Library Parts can be installed locally, using the procedure outlined in Appendix 1 and the same parts can then be selected from this locally installed library. With the package having two emitters, it is difficult to realise emitter stabilisation at >1 GHz. As a result, collector stabilisation is implemented. One of the biasing resistors (Rb) is adjusted to provide a collector current of 10 mA. To obtain a low noise figure, an inductor is used to decouple the biasing. The frequency response of the amplifier has a peak at 4 GHz and adding a 0.7pF capacitor at the output provides a flat frequency response. Increasing the collector current provides a higher gain and a flatter frequency response. The resulting amplifier schematic is shown in figure 2.25. The node voltage annotation is shown. For the microwave amplifier of figure 2.25, the maximum possible gain is required and the emitters are connected to ground. The maximum collector current is 25 mA, so that a 13 mA quiescent collector current is safe. That is also the collector current used for the parameters specified in the data sheet [23]. The resistors Rb can be adjusted to ensure that the quiescent collector current of 10 mA is obtained. As is normal for RF and microwave amplifiers, 50 Ω source and load impedances are used. Figure 2.25. Transistor amplifier circuit diagram. RF Electronics: Design and Simulation 23 www.cadence.com/go/awr

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