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Guide to the RF Amplifier

Author: Tanssion Date: 2023-08-08 Hits: 0

Ⅰ. The concept of RF amplifier
Ⅱ. Different types of RF amplifiers
Ⅲ. Application fields of RF amplifiers
Ⅳ. What does an RF amplifier do?
Ⅴ. What is the purpose of an RF amplifier?
Ⅵ. How does RF power work?
Ⅶ. What are the advantages of RF amplifier?
Ⅷ. What are the materials used in RF amplifier?
Ⅸ. What is the voltage of an RF amplifier?
Ⅹ. RF amplifier circuit

In modern wireless communication systems, RF amplifiers play a vital role. It is responsible for amplifying low-power, high-frequency radio frequency signals to a sufficient power level to ensure the stability and reliability of signal transmission. Below we will learn about the relevant knowledge of RF amplifiers.

Ⅰ. The concept of RF amplifier

The radio frequency power amplifier (RF PA) is the main part in the transmission system, and its importance is self-evident. In the pre-stage circuit of the transmitter, the power of the radio frequency signal generated by the modulation oscillator circuit is very small. It needs to go through a series of amplification (buffer stage, intermediate amplification stage, final power amplification stage) to obtain enough radio frequency power before it can be fed to the antenna for radiation. In order to obtain a large enough radio frequency output power, we must use a radio frequency power amplifier. After the modulator generates the radio frequency signal, the radio frequency modulated signal is amplified to sufficient power by the RF PA, and then transmitted by the antenna through the matching network.

Ⅱ. Different types of RF amplifiers

RF amplifier is the core device in the communication system, and its types are not the same.

1. Log Amplifier

A logarithmic amplifier is an amplifier with a gain curve where the output voltage is a multiple of the natural logarithm of the input voltage. This type of amplifier is designed specifically for applications that require this behavior.

2. Linear Amplifier

A linear amplifier is a general-purpose amplifier, sometimes called a "gain block," that provides signal gain in a system. Since they are not inputs or outputs to the system, they are usually not a determining factor in the dynamic range of the system. The power level is higher than LNA, but lower than PA. So this is an amplifier choice that trades off linearity, noise figure cost, size, and power consumption. While the requirements for linear amplifiers are not strict, they must not degrade the signal in any significant way. These amplifiers are never a significant part of the system, but they also affect the overall system.

3. Broadband Amplifier

Broadband amplifiers, or broadband amplifiers, are designed to provide moderate gain over a wide bandwidth while maintaining a low noise figure. These types of amplifiers are often used in receiver circuits in front of antennas when a low noise amplifier is not required, and within receivers when additional gain is required and noise needs to be controlled.

4. Variable Gain Amplifier

A variable gain amplifier is an amplifier whose gain is controllable (and sometimes programmable). It can be achieved by using a variable gain circuit or a variable attenuator and a fixed gain amplifier, depending on the application. Also known as linear-to-log converters, these amplifiers are often used as part of a closed-loop control circuit to maintain consistent signal power levels in the main signal path.

5. Gain Block Amplifier

Gain block amplifiers (or gain blocks) are similar to wideband amplifiers, except that they are generally not designed for low noise figure and have greater gain than wideband amplifiers. Gain block amplifiers are used in IF, RF, and microwave transmitter applications and may include models with narrow or wide bandwidths. It usually depends on the type of application for which it is designed.

6. Bi-directional Amplifier

A bidirectional amplifier is a combination transmitter and receiver designed to act as an intermediate node that receives a weak signal and amplifies that signal for retransmission and capture at an electrically distant location. Bi-directional amplifiers are often used to extend communication networks to remote locations without installing additional infrastructure. It can be used to cover larger land areas, or used with coaxial transmission lines to extend signaling or communication systems to greater distances underground or within facilities. A bidirectional amplifier usually requires a good low noise amplifier and power amplifier. For models that handle high-throughput digital communications, bi-directional amplifiers may need to have the necessary demodulation and modulation circuitry built in to fully recreate and retransmit the signal, ensuring the highest fidelity at the destination.

7. Coaxial and Waveguide Power Amplifiers

The power amplifier is the main amplifier in the radio frequency front end of the transmitter, converting the low power signal from communication and radar equipment into a high power transmission signal sent to the antenna. The goal of a power amplifier is to increase signal gain to high power levels without degrading signal quality. Because this is often a difficult design challenge with trade-offs, some power amplifiers can be optimized for parameters best suited for pulsed radar, CW radar, digital communications, or other applications that require the use of these devices.

Because the power amplifier must also handle various types of loads, and some loads may cause damaging reflections. Therefore, the general power amplifier also includes a protection circuit. Power amplifiers can also be used with coaxial connectors or even waveguide connectors when the power level or operating frequency is high enough.

8. Low Noise Amplifier

Low noise amplifiers are the easiest microwave amplifiers to understand. It is designed to accept very low level signals because the low input power results in relatively little non-linear effects in the amplifier. Like the signal you see at the end of a lossy transmission medium and amplifies it with minimal added noise. It is important to note that, in addition to adding noise, the noise is also amplified by the same gain as the signal. This also means that a LNA or any other amplifier cannot improve the signal-to-noise ratio (SNR), it can only increase the power level of the signal and noise. If the gain is narrowband, the amplifier may filter some out-of-band noise or signal, but also cannot improve the signal-to-noise ratio due to in-band noise.

If the signal-to-noise ratio doesn't improve, why bother with amplification? The reason is that the cascading in the receiver has losses, and this loss applies equally to the signal and the noise. If the noise level is already well above the noise floor, the loss will not significantly reduce the signal-to-noise ratio of the signal. Therefore, the noise figure of the LNA usually dominates the noise figure of the entire receiver chain. Ultimately, the signal detector at the end of the signal chain (usually an analog-to-digital converter (ADC) in modern systems) has a detectable voltage range, and the receiver designer will use amplifier stages throughout the receiver chain to make the received The signal power can be matched to the detectable voltage range of the ADC to detect the signal of interest.

LNAs are usually narrowband, or at least bandwidth-limited devices. Usually in order to optimize the noise figure of the transistors in the amplifier, we will create a narrowband matching network. Modern LNAs can achieve extremely high gain at low noise figure, for example up to 40dB gain at low frequency noise figure less than 1dB.

9. High Reliability Amplifier

High reliability amplifiers are a class of amplifiers that meet or exceed high reliability standards or expectations and are typically used in automotive, aerospace, space, or military/defense applications. Typically, these amplifiers are more resilient than their standard counterparts, and the ratings refer to the amplifier's expected lifetime under varying operating conditions.

Ⅲ. Application fields of RF amplifiers

A radio frequency amplifier is an electronic device used to amplify radio signals to higher power levels. They play an important role in modern communication and broadcasting systems and have many different applications, including:

1. Military applications: RF amplifiers are also widely used in military radar and communication systems. These devices need to be able to operate in harsh environments and stay connected by resisting interference and interference.

2. Medical diagnosis: Medical imaging and other medical equipment require the use of RF amplifiers to transmit signals from the body. For example, MRI machines use radio-frequency amplifiers to generate a magnetic field and read the feedback signals to produce images of the anatomy of the human body.

3. Scientific research applications: RF amplifiers are also used in scientific research fields, such as astronomy, physics and material science. These applications require high precision and high sensitivity instrumentation in order to capture and analyze weak RF signals.

4. Communication system: RF amplifiers are widely used in wireless communication systems, such as mobile phones, satellite communications, radio broadcasting, etc. These systems need to amplify the transmitted RF signal to a sufficient power level to transmit the signal over long distances.

In short, RF amplifiers play a vital role in military applications, medical diagnosis, scientific research applications, and communication systems, and have a wide range of applications.

Ⅳ. What does an RF amplifier do?

A radio-frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency signal into a higher-power signal.

Ⅴ. What is the purpose of an RF amplifier?

Radio frequency power amplifiers are designed to convert a low-power radio frequency signal to a higher-power signal. Typically, RF amplifiers can amplify signals in any band of frequencies from 10 kHz to 100,000 MHz.

Ⅵ. How does RF power work?

A radio frequency power harvesting system can capture and convert electromagnetic energy into a usable direct current (DC) voltage. The key units of an RF power harvesting system are the antenna and rectifier circuit that allows the RF power or alternating current (AC) to be converted into DC energy.

Ⅶ. What are the advantages of RF amplifier?

The RF amplifiers have greater gain that is they have better sensitivity. They have better ability to amplify weak signals received by the receiver. The RF amplifiers have better selectivity i.e., better ability to select the wanted signals among the various incoming signals.

Ⅷ. What are the materials used in RF amplifier?

RF semiconductor materials include gallium arsenide (GaAs), gallium nitride (GaN), silicon (Si), and silicon carbide (SiC). These materials are significant in circuits such as RF filters, RF power amplifiers, RF low noise amplifiers, and RF switches.

Ⅸ. What is the voltage of an RF amplifier?

DC power: Most IC RF amplifiers operate from a supply voltage in the 1.8- to 6-V range. Current levels vary with supply voltage and the power generated and can range from 20 mA to over 100 mA. If the amplifier has a standby or low-power mode, current level should drop to no more than a few milliamps.

Ⅹ. RF amplifier circuit

The figure below shows the circuit diagram of a first-stage RF amplifier using NPN transistors. It is a small signal amplifier that uses a parallel tuned circuit as the load impedance. The parallel output tuning circuit is tuned to the input desired signal frequency. The output of the receive antenna is a transformer coupled to the base of the transistor.

The secondary coil of the input tuning circuit is tuned to the input desired signal frequency by means of ganged tuning capacitors. In fact, the tuning capacitors, i.e. variable air capacitors, on the input and output sides of the RF amplifier are combined. Besides that, small trimmer capacitors are connected in parallel with these tuning capacitors for RF alignment.

Self-biasing is provided by resistors R1 and R2 and the RE-CE component. A decoupling network consisting of resistor Rb and capacitor Cb is placed in the collector supply lead.

The signal developed on the amplified R.F. collector tuning circuit is coupled through a step-down transformer providing impedance matching between the high impedance of the R.F. Low impedance of amplifier collector circuit and subsequent base to emitter circuit. In addition, the collector is connected to a suitable point on the primary of the output transformer so that the load impedance of the collector is optimized.


Frequently Asked Questions

1、What is the RF amplifier?
Radio frequency power amplifiers are designed to convert a low-power radio frequency signal to a higher-power signal. Typically, RF amplifiers can amplify signals in any band of frequencies from 10 kHz to 100,000 MHz.
2、What RF means?
Radio frequency. Radio frequency (RF) is a measurement representing the oscillation rate of electromagnetic radiation spectrum, or electromagnetic radio waves, from frequencies ranging from 300 gigahertz (GHz) to as low as 9 kilohertz (kHz).
3、Where are RF amplifiers used?
Whenever people need to magnify a radio frequency signal into a higher power signal, the RF amplifier plays a pivotal role. They are used in commercial and defense avionics, space and deep space, electronic warfare, naval applications, mobile internet, satellite communication, and wireless communications.
4、How is RF power generated?
All RF power amplifiers for high-power hadron accelerators employ vacuum tube technology. Vacuum tubes use d.c., or pulsed, voltages from several kilovolts to hundreds of megavolts depending upon the type of tube, the power level and the frequency.
5、What is the output power of an RF amplifier?
This is the maximum power output possible with a 50-Ω load at the highest supply voltage. It's usually given in dBm, referenced to 1 mW. The typical range is typically 12 to 28 dBm.

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