Radio frequency wireless communication system transmitting and receiving
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Radio frequency wireless communication system transmitting and receiving

Posted Date: 2024-01-18

What is a radio frequency circuit

Radio frequency circuits are circuits specially designed to process high-frequency signals and are widely used in communications, radar, remote sensing and other fields. Radio frequency circuits can complete functions such as signal transmission, modulation and demodulation, amplification, and filtering.

Radio frequency circuits can be classified into many categories based on their functions and application areas. The following are several common RF circuit classifications:

1. According to frequency range:

- Low-frequency radio frequency circuits: The frequency range is generally between several hundred kilohertz (kHz) and several megahertz (MHz).

- Intermediate frequency (medium frequency) radio frequency circuit: The frequency range is generally between a few megahertz (MHz) to tens of megahertz (MHz).

- High-frequency radio frequency circuits: The frequency range is generally between tens of megahertz (MHz) to hundreds of gigahertz (GHz).

- Millimeter wave radio frequency circuit: The frequency range is generally above several hundred gigahertz (GHz).

2. According to application areas:

- Communication radio frequency circuits: including radio frequency front-ends, antennas, modems, etc. in wireless communication systems.

- Radar RF circuit: used in transmitting and receiving modules, filters, amplifiers, etc. in radar systems.

- Satellite communication radio frequency circuit: handles frequency conversion, amplification, modulation and demodulation, etc. in satellite communication.

3. According to function and composition:

- Amplifier: used to amplify the amplitude of a signal.

- Mixer: used to perform frequency modulation, demodulation or frequency conversion operations on signals.

- Frequency synthesizer: used to generate signals of specific frequencies.

- Filter: used to select or exclude signals in a specific frequency range.

- Antenna: used to send and receive wireless signals.

4. According to the packaging form:

- Chip-level RF circuit: A RF circuit packaged in the form of a chip, usually used in integrated circuits.

- Module-level RF circuit: RF circuit packaged in module form, with higher integration and ease of application.

The main application field of radio frequency circuits is wireless communications. Figure 1.1 is a block diagram of a typical wireless communication system. The following uses this system as an example to analyze the role of radio frequency circuits in the entire wireless communication system.


Figure Typical RF system block diagram

This is a system model of a wireless communication transceiver (tranceiver), which includes a transmitter circuit, a receiver circuit and a communication antenna. This transceiver can be used in personal communications and wireless local area networks. In this system, the digital processing part mainly processes digital signals, including sampling, compression, encoding, etc.; then it is converted into analog form through the A/D converter and enters the analog signal circuit unit.

The analog signal circuit is divided into two parts: the transmitting part and the receiving part.

The main function of the transmitting part is: the low-frequency analog signal output by the digital-to-analog conversion and the high-frequency carrier provided by the local oscillator are up-converted into a radio frequency modulated signal through the mixer, and the radio frequency signal is radiated into the space through the antenna. The main function of the receiving part is: the space radiation signal is coupled to the receiving circuit through the antenna. The received weak signal is amplified by the low-noise amplifier and then down-converted with the local oscillation signal through the mixer into a signal containing an intermediate frequency signal component. The function of the filter is to filter out the useful intermediate frequency signal and input it into the analog-to-digital converter to convert it into a digital signal, and then enter the digital processing part for processing.

The difference between radio frequency circuits and analog circuits

Radio frequency circuits and analog circuits are two important concepts in the electronic field. There are some differences between them, which are mainly reflected in the following aspects:

Frequency Range:

- Radio frequency circuits: Radio frequency circuits are mainly focused on processing and transmitting high-frequency signals, usually covering the frequency range from a few hundred kilohertz (kHz) to tens of gigahertz (GHz). Radio frequency circuits are commonly used in wireless communications, radar, satellite communications, radio frequency identification (RFID) and other fields.

- Analog circuits: Analog circuits are widely used in low-frequency signal processing, and their frequency range usually includes a few hertz (Hz) to hundreds of kilohertz (kHz).

Signal processing method:

- Radio frequency circuit: Radio frequency circuit faces frequency-oriented signal processing, involving components and technologies such as antennas, filters, amplifiers, mixers, modulators, and demodulators. Radio frequency circuits usually need to consider transmission line characteristics, impedance matching, power amplification and other issues.

- Analog circuits: Analog circuits mainly process continuous voltage and current signals, involving amplifiers, filters, operational amplifiers, analog switches, etc. Analog circuits focus on processing, amplifying, transmitting, and filtering various voltages and currents.

Anti-interference ability:

- RF circuit: RF circuit requires good anti-interference ability, because RF signals are more susceptible to electromagnetic interference. For this reason, RF circuits often use special shielding and filtering measures to reduce interference from other devices or the environment.

-Analog circuits: Analog circuits also require certain anti-interference capabilities, but compared to radio frequency circuits, the requirements for interference are more relaxed. Analog circuits pay more attention to signal accuracy, stability and linearity.

The above are some basic differences between RF circuits and analog circuits. RF circuits mainly focus on the transmission and processing of high-frequency signals, while analog circuits deal more with low-frequency signals and continuous voltage/current signals. Despite their differences, there are many applications where RF and analog circuits intersect and combine with each other.

Review Editor: Huang Fei


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