RF Power Amplifier Design Parameters

October 12, 2021 Cadence System Analysis

Key Takeaways

  • RF power amplifiers are devices used in RF chains to increase the power of the input signal to achieve high power output. 

  • Impedance matching is required in RF power amplifiers to deliver maximum power to the load from the source.

  • The RF power delivered to the load is a key parameter influencing RF power amplifier design.

Communication network graphic

 In modern communication systems, RF power amplifiers are the last active component in an RF chain

In modern communication systems, RF power amplifiers are the last active component in an RF chain, and RF power amplifier design is a critical factor affecting the performance of the entire system. The efficiency, reliability, and compactness of an RF power amplifier matters greatly in communication systems. They are used in RF chains to increase the power of an input signal to achieve high power output and they also amplify RF signals so that the system bandwidth, coverage, and efficiency increase. 

RF power amplifiers are applied in many communication systems, including:

  • AM and FM radio broadcasting systems
  • Base stations
  • Antenna systems
  • Television receivers
  • Wireless networks

Let’s take a closer look at how RF power amplifiers are designed.

The Stages of an RF Power Amplifier 

RF power amplifiers are comprised of a few different stages:

  1. Input impedance matching network: Impedance matching is required in RF power amplifiers to deliver maximum power to the load from the source. Impedance matching networks are introduced in the input side of RF power amplifiers to match with the typical input impedance of 50 ohms.

  2. Amplifiers stages: Depending on the input signal and output power required, the gain is calculated. Based on the gain calculated, the number of amplifier stages is determined. If multiple amplifier stages are present, then either parallel or cascade connections are utilized. 

  3. Biasing network: These are the active components used in an RF power amplifier necessitating a biasing circuit. The biasing network supplies the bias voltages to the RF amplifier stages. 

  4. Accessories network: These are the circuits used for improving the linearity, stability, and performance of RF power amplifiers.

  5. Output impedance matching network: On the output side of the RF power amplifier, impedance matching networks are connected to match the output impedance of the RF power amplifier to 50 ohms. 

RF Power Amplifier Design Parameters

While designing RF power amplifiers, certain parameters are of great importance. In the following section, some important parameters for RF power amplifier design are discussed. 

  1. Output power: The RF power delivered to the load is a key parameter influencing RF power amplifier design. Conjugate impedance matching is normally employed in RF power amplifiers to deliver maximum power to the load. 
  2. Power amplifier efficiency: The term ‘power efficiency of RF power amplifiers’ is defined by the ratio of the difference between output RF power and RF input power to the input DC power. The power amplifier efficiency is maximum at maximum output RF power. 
  3. Signal gain: The signal gain depends on the RF power amplifier input and output specifications. Depending on the gain required, the amplifier stages are designed. 
  4. Linearity: The non-linear characteristics of the RF power amplifier are detrimental to the amplifier’s operation. By maintaining the linearity of RF power amplifier stages, distortions in amplitude, phase, and frequency can be minimized. 
  5. Modulation scheme: The selection of a modulation scheme in a communication system is important in RF amplifier design, as it influences the efficiency and linearity performance of the amplifier stages. 
  6. Crest factor: The parameter crest factor in an RF power amplifier is equal to the square root of the ratio of peak signal power to average signal power (PAPR). The PAPR determines the input power back-off, which is important in achieving good linearity.

Advancements in communication engineering, such as 3G, 4G, and 5G, demands robust RF power amplifier designs with excellent parameters such as efficiency, linearity, bandwidth, etc. Cadence software offers a full suite of tools for designing RF power amplifiers.

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