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RFIC PA Development for Communication and Radar Systems

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RFIC PA Development for Communication and Radar Systems 2 www.cadence.com/go/awr Design Overview This white paper highlights the use of the Cadence ® AWR Design Environment ® platform for the design of PAs and examines some of the challenges in designing RFIC-based PAs for future 5G communication systems. Future 5G communications, which aim to increase mobile broadband traffic and provide higher data rates, will rely on networks implemented with a wide array of new technologies. 5G networks will require adding more spectrum, making that spectrum more efficient, and building out ultra-dense network configurations. Of the RF and microwave hardware components that will support all these different systems, three main trends will continue to be true. First, performance, such as bandwidth, linearity, and efficiency, will be critical and will have a major impact on PAs. Second, integration, which is often addressed with multi-technology modules but could benefit from the RF integrated circuit (RFIC) devices described above, will be critical for bringing high-performing, cost-effective communications products to market quickly. Finally, the escalating cost of product development for complex systems will require more coordinated engineering efforts. PA Basics PAs are the final active device in the transmitter chain. They are responsible for boosting the signal strength, with help from the gain of the antenna, to a level that is sufficient for overcoming channel losses incurred during transmission. PAs consume the most power among the RF front-end components, from a few hundred milliwatts for a cellular phone up to hundreds of watts for a base station. As a result, they receive considerable design attention to improve their power-added efficiency (PAE), which will be discussed below. A generalized PA circuit consists of an input-matching network, an input-bias network, an active device, an output-bias network, and an output-matching network, as shown in Figure 1. The load can be an antenna, a switch, or an additional PA stage. Figure 1: Main components of a PA, shown with source and load blocks The output-matching network converts the impedance of the load to an impedance that provides proper functionality of the PA. Output and input bias networks provide the operating points for the active devices, which is either a single transistor or multiple transistors in parallel. The input matching network converts the input impedance of the active device to an impedance that provides proper functionality of the PA. The source can be a signal generator, a previous block of a trans- mitter, or an amplifier stage in case of a multi-stage PA. Two important characteristics of an RF PA are gain and output power. Gain, the mean ratio of the power at the output port to the power at the input port, 10 log (Pout/Pin), is often specified as a function of input frequency and input-power level. Power gain has several definitions: the transducer power gain, the operating power gain, and the available power gain 1 . The transducer-power gain is defined as the ratio of the power delivered to the load to the power available from the source: The operating power gain is defined as the ratio of the power delivered to the load to the input power to the amplifier: The available power gain is defined as a ratio of the power available from the amplifier to the power available from the source: In general, a PA exhibits relatively constant gain across a wide range of input-power levels with the gain dropping as the output power approaches the device's saturation region. This effect is known as gain compression. Gain as a function of power is simulated/measured by sweeping the power level of the signal generator and measuring the output power of the PA. *Guillermo Gonzalez, Microwave Transistor Amplifiers: Analysis and Design, Prentice Hall, second edition, 1997.

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