RF amplifier｜Power supply applications

What is the RF amplifier?

An RF (Radio Frequency) amplifier is an electronic device that amplifies high-frequency signals to deliver a significant amount of power. It is also known as an RF power amplifier, RF power supply, high-frequency power supply, or microwave power amplifier. A primary application is plasma generation for semiconductor manufacturing processes, where the plasma is used for surface treatments like etching and sputtering.

RF Power Transistor | Matsuada Precision

What is the frequency of the RF amplifier?

RF amplifiers operate over a wide range of frequencies, from kilohertz (kHz) to gigahertz (GHz). For many industrial and scientific applications, their use is often restricted to specific frequencies defined by regulations for ISM (Industrial, Scientific, and Medical) bands, such as 13.56 MHz and 2.45 GHz. In addition, notification and permission may be required for use.

How does the RF amplifier work?

An RF amplifier's basic components include an oscillator, a DC power supply, transistors, and a matching circuit.

Oscillator

The oscillator generates the frequency of the RF signal. The 13.56 MHz frequency is mainly used in industrial applications.

DC power supply

The DC power supply provides the bias voltage and current to operate the transistors. Variable DC power supplies up to about 100 V are used. The current or power varies from a few hundred watts to several kilowatts or tens of kilowatts, depending on the application.

Transistor

RF power amplifiers typically use transistors as the amplifying element.
The following is a list of commonly used transistor types.

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LDMOS (Lateral Diffusion Metal Oxide Semiconductor)

Advantages: High power handling capability and efficiency, suitable for RF applications. It combines the advantages of MOSFET and BJT.
Function: Often used in high-power RF amplifiers and can switch effectively at high frequencies.

LDMOS device manufacturers: Ampleon: https://www.ampleon.com/; NXP Semiconductors: https://www.nxp.com/; Infineon Technologies: https://www.infineon.com/; STMicroelectronics: https://www.st.com/; Integra Technologies: https://www.integratech.com/; MACOM: https://www.macom.com/; Wolfspeed (formerly Cree): https://www.wolfspeed.com/; Qorvo: https://www.qorvo.com/; Analog Devices: https://www.analog.com/; Microchip Technology: https://www.microchip.com/

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MOSFET (Metal Oxide Semiconductor Field Effect Transistor):

Advantages: fast switching, excellent thermal stability, high efficiency. Often used in applications requiring high-speed switching.
Function: Fast on/off, controls current flow, effectively converts DC voltage to high-frequency AC waveforms.

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GaN (Gallium Nitride) Transistors

Advantages: excellent efficiency, high breakdown voltage, very fast switching speed. These properties have made GaN increasingly popular in high-frequency applications.
Function: GaN devices used in state-of-the-art power supplies can support high frequencies (up to several GHz) and provide higher power densities than traditional silicon-based devices.

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Matching network

The matching network is the impedance matching circuit with the load.

Operating principles: Input stage: RF signal is applied to the input of the transistor (gate of LDMOS/MOSFET/GaN).; Amplification: Transistors amplify input signals by converting DC power from the power supply into RF power.; Output stage: The amplified signal is sent to the output (drain of LDMOS/MOSFET/GaN).; Matching Network: The input and output matching networks are crucial for optimizing power transfer and ensuring proper impedance matching with the signal source and the load.; Bias: The DC bias circuit sets the operating point of the transistor for proper amplification.

Efficiency: Recent RF amplifiers have improved power conversion efficiency and energy conservation through the use of high-efficiency RF amplifiers, with some reaching power conversion efficiencies of 90% or more. Improved power conversion efficiency has reduced heat generation and the burden of cooling, resulting in lighter, more efficient models.
The built-in fast auto-matching feature allows for quick response to load variations, maintaining efficiency by minimizing reflected power, and dynamic power management, which adjusts the DC supply voltage based on output power requirements, can significantly improve efficiency.

Issue: • Heat dissipation: High power operation generates considerable heat and requires effective thermal management.; • Linearity: Maintaining linearity while achieving high efficiency is an important issue, especially for modern modulation schemes.; • Stability: It is very important to prevent unwanted oscillations and ensure stable operation under various conditions.; • Harmonic Suppression: Harmonic components of the RF signal must be suppressed, typically to levels below -35 dBc (decibels relative to the carrier).; • Improved reliability: High reliability is required for use in critical processes such as semiconductor manufacturing equipment.

To address these issues, the high output power, efficiency, and linearity required for RF power supplies are continuously being improved by optimizing RF circuit design, employing high-performance semiconductor devices, and utilizing digital control technology. In addition, by feeding our experience and know-how as an equipment manufacturer back into the design process, we are developing highly practical RF power supplies.