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RF Electronics Chapter 8: Amplifiers: Stability, Noise and Gain Page 276 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Some MMIC's are made using InGaP HBTs (indium gallium phosphide Heterojunction Bipolar Transistors). Mini-Circuit's MAR, ERA, Gali and Lee series of amplifiers are examples of this and they require a constant current source and have a typical circuit diagram as shown in figure 8.1. The Mini-Circuits [1] ERA-3+ amplifier has a bandwidth of DC to 3 GHz, and a 21 dB gain and NF of 2.6 dB at 1 GHz and operates using a 35 mA supply with a typical device voltage of 3.2V. The constant current supply is typically obtained using a series resistor in series with an inductor, as shown in figure 8.2. A suitable constant supply is obtained, by using a resistor to set the current supplied to the MMIC as shown in figure 8.2. The RF loading of that resistor is minimised by having a large inductor in series with the resistor. Since the resistor is typically, 600 for a 12 Volt supply voltage, in many applications, a slightly reduced gain can be tolerated and the inductor can be removed. This series resistor, together with the DC feedback resistor, between the collector and base of the transistor in figure 8.1, result in a stable quiescent current as the temperature changes. Figure 8.2 Typical connection requirement for an MMIC. Other MMIC's are made using GaAs e-pHEMTs (Gallium Arsenide Enhancement Mode Pseudomorphic High Electron Mobility Transistors). A typical example of this is Mini- Circuit's PMA-5453+ [2] amplifier, which has a bandwidth of 50 MHz to 6 GHz and a 19.3 dB gain, a NF of 0.7 dB and IP3 of 35 dB at 1 GHz. It operates using a fixed 3 V supply. The typical MMIC connection is similar to Figure 8.2 with the resistor in the power supply replaced by a short circuit, to provide a constant DC voltage at the MMIC output, but not cause any RF loading due to the power supply. Other manufacturers have devices with a similar performance to the above examples and there are hundreds of different commercial MMIC's available. In addition to low power MMIC's many manufacturers also produce high lower amplifier modules. Most MMIC devices are unconditionally stable. However, since these devices have very wide bandwidths, microwave layout techniques must be used to ensure that the devices remain stable. As a typical example it is essential that the inductance of the ground pin connections of the MMIC are kept as low as possible. This is achieved by ensuring that the earth pins of the MMIC are soldered to a large ground plane and that a via connecting the top ground-plane to the bottom ground-plane is very close to the earth pin of the MMIC in the Microstrip PCB layout. Like the ground planes of figures 6.44, 7.67 or 9.59. These amplifier modules and MMIC's can now be used for the majority of RF and microwave designs. There are applications, such as ultra-low noise amplifiers, millimetre wave amplifiers and high power amplifiers, where amplifier modules and MMIC's cannot be used for either performance or economic reasons. For such designs, a knowledge of amplifier stability, NF and gain circles, which are described in this chapter. is essential. RF Electronics: Design and Simulation 276 www.cadence.com/go/awr

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