An “inverse Class D” amplifier, also known as a Class E amplifier, is a type of high-efficiency radio-frequency (RF) amplifier used primarily in applications such as radio transmitters, wireless communication systems, and power amplification for electromagnetic energy sources. It’s worth noting that an inverse Class D amplifier operates differently from traditional audio Class D amplifiers, which are designed for audio signal amplification.
Here’s how an inverse Class D amplifier (Class E amplifier) works:
- Switching Operation: Like Class D amplifiers, Class E amplifiers operate using a switching technique. However, the main difference lies in the purpose and frequency of the switching.
- High-Frequency Switching: Inverse Class D amplifiers are designed to work at very high frequencies, often in the radio-frequency (RF) range, typically above 1 MHz. This high frequency makes them suitable for applications where high-power RF amplification is required.
- Transistor Switching: Class E amplifiers typically use high-power, high-frequency transistors, such as MOSFETs or GaN (gallium nitride) devices, as the switching elements. These transistors rapidly switch on and off at the amplifier’s operating frequency.
- Power Conversion: Instead of amplifying audio signals, Class E amplifiers are used to amplify electromagnetic signals, such as RF signals generated by oscillators or other RF sources. The amplifier’s job is to efficiently convert DC power into high-power RF output.
- Square-Wave Drive: In a Class E amplifier, the switching operation generates a square-wave drive signal. The transistors are rapidly turned on and off to create a square-wave output.
- Efficiency: Class E amplifiers are known for their high efficiency, often exceeding 90% or even 95%. This efficiency is achieved by minimizing the time that the transistors spend in the “on” state (to minimize power dissipation) and by ensuring that the square-wave output is highly sinusoidal (to minimize harmonic distortion).
- Matching Networks: To ensure optimal power transfer, Class E amplifiers use matching networks at the input and output to match the amplifier’s impedance to the source and load impedance, respectively.
- Applications: Class E amplifiers are commonly used in RF transmitters, especially in applications like amateur radio, wireless communication, and power amplification for RF sources. They are favored for their high efficiency and ability to deliver high RF power output.
In summary, an inverse Class D amplifier, or Class E amplifier, is designed for high-frequency RF applications where it efficiently converts DC power into high-power RF signals. It operates using a switching technique and is known for its high efficiency and suitability for RF amplification tasks. This is in contrast to traditional Class D audio amplifiers, which are designed for low-frequency audio signal amplification.
