5G: Power Amplifier
Sumber: https://resources.system-analysis.cadence.com/blog/msa2021-rf-power-amplifier-design-parameters
Dalam sistem komunikasi modern, penguat daya RF adalah komponen aktif terakhir dalam rantai RF, dan desain penguat daya RF merupakan faktor penting yang memengaruhi kinerja seluruh sistem. Efisiensi, keandalan, dan kekompakan penguat daya RF sangat penting dalam sistem komunikasi. Mereka digunakan dalam rantai RF untuk meningkatkan kekuatan sinyal input untuk mencapai output daya tinggi dan mereka juga memperkuat sinyal RF sehingga bandwidth, cakupan, dan efisiensi sistem meningkat.
Penguat daya RF diterapkan di banyak sistem komunikasi, termasuk:
- Sistem penyiaran radio AM dan FM
- Base Station
- Sistem antena
- Penerima televisi
- Jaringan wireless termasuk 4G dan 5G
5G adalah salah satu teknologi paling penting dan powerful yang pernah menjangkau pasar di bidang komunikasi wireless. Menawarkan peningkatan signifikan dalam kecepatan data, latensi, dan kapasitas dibandingkan dengan 4G, 5G siap menjadi teknologi yang benar-benar transformatif di industri dan dunia.
Namun, peningkatan kinerja yang radikal ini menimbulkan beban yang meningkat dan persyaratan yang lebih ketat untuk perangkat keras frekuensi radio (RF) yang mendasarinya. Salah satu perangkat keras RF yang paling berperan adalah power amplifier (PA), perangkat yang kepentingannya semakin meningkat dengan implementasi 5G.
Mari kita lihat lebih dekat bagaimana penguat daya RF dirancang.
The Stages of an RF Power Amplifier
RF power amplifiers are comprised of a few different stages:
- 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.
- 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.
- 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.
- Accessories network: These are the circuits used for improving the linearity, stability, and performance of RF power amplifiers.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
To help ease the challenges of designing RF PAs for 5G, power amplifier modules (PAMs) have become an important tool in recent years.
In this post, we'll talk about PAs, their role in 5G, and how Qorvo leverages PAMs to help support the 5G infrastructure of the future.
PAM
What Is a PA? When working with RF signals, especially at the higher frequency bands of 5G, voltage levels can be extremely low. This is a challenge because the electromagnetic (EM) signal becomes more susceptible at lower amplitudes to the effects of system-level noise (i.e., signal-to-noise ratio decreases). On top of this, lower-voltage signals generally lack the strength necessary to drive downstream circuitry or antennas.
To address these challenges, engineers use PAs. An RF PA is a circuit block that serves to increase the amplitude, power output, or drive capacity of an RF signal. Generally, RF PAs live near the system antennas to provide a transmitting antenna with a high-power signal.
With a PA, the goal is to boost the signal while maintaining a high level of fidelity from input to output. For these reasons, linearity, efficiency and output power are important specifications for a PA.
PA Design Challenges Historically, PAs and their surrounding circuitry were designed using discrete components on a board. While this approach has served the industry for many years, the efficacy of this approach is coming into question as several nontrivial design challenges emerge.
One of these challenges is being able to balance the tradeoffs among area, cost, performance and power consumption. Generally, these specifications tend to conflict with one another, and designers must know how to optimize their circuits to balance the tradeoffs in an optimal way for their given application. Balancing these tradeoffs is increasingly difficult when using discrete components as considerations like part selection, component interoperability, and layout impact performance.
This is further confounded when moving to 5G, where systems need to cover wider bandwidths and higher frequency ranges. Today's systems require an average instantaneous bandwidth of up to 400 MHz while operating at frequencies up to 4 GHz. The challenge is now maintaining the aforementioned system tradeoffs while also providing performance over this frequency band.