In-depth analysis of the principles and applications of RF circuits

　　What is an RF circuit?

　　RF is abbreviated as RF. RF refers to radio frequency current, which is a type of high-frequency AC electromagnetic wave. AC with a change of less than 1000 times per second is called low-frequency current, and more than 1000 times per second is called high-frequency current. RF is such a type of high-frequency current.

　　An RF circuit refers to a circuit in which the electromagnetic wavelength of the processed signal is on the same order of magnitude as the circuit or device size. At this time, due to the relationship between device size and wire size, the circuit needs to be handled using the relevant theory of distribution parameters. Such circuits can all be considered RF circuits, and there are no strict frequency requirements. For example, long-distance AC transmission lines (50 or 60Hz) sometimes also require RF theory.

　　RF circuit block diagram

　　The principle of RF circuits

　　We will explain the principle of RF circuits in detail using ordinary mobile phone RF circuits:

　　1. Structure and Working Principle of the Receiving Circuit:

　　During reception, the antenna converts the electromagnetic waves sent by the base station into weak AC current signals, filters them, amplifies them at high frequencies, and sends them into the intermediate frequency for demodulation, obtaining the reception baseband information (RXI-P, RXI-N, RXQ-P, RXQ-N); Send to the logic audio circuit for further processing.

　　Circuit Analysis:

　　(1) Circuit structure

　　The receiving circuit consists of an antenna, antenna switch, filter, high amplifier (low-noise amplifier), intermediate frequency integrated block (receiver demodulator), and other circuits. Early mobile phones had first-stage and two-stage mixer circuits, with the purpose of lowering the received frequency before demodulation (as shown in the figure below).

　　Block diagram of the receiver circuit

　　2. Structure and working principle of the transmitting circuit

　　During transmission, the transmit baseband information processed by the logic circuit is modulated into the transmit IF signal, which is then converted to a frequency of 890M-915M (GSM) using TX-VCO. After amplification by the amplifier, the antenna converts it into electromagnetic waves that are radiated outward.

　　Circuit Analysis:

　　(1) Circuit structure.

　　The transmitting circuit consists of an internal transmitter modulator and transmitter phase detector within the intermediate frequency; It consists of circuits such as the transmit voltage-controlled oscillator (TX-VCO), power amplifier (power amplifier), power controller (power control), and transmitting transformer. (See the figure below)

　　3. Structure and working principle of local oscillator circuits: (local oscillator circuit, phase-locked loop circuit, frequency synthesis circuit)

　　This circuit generates four segments of local oscillator frequency signals (GSM-RX) with no information at all; GSM-TX; DCS-RX; DCS-TX); Sent into the IF to demodulate the received signal during reception; During launch, the baseband information is modulated and phase identification is conducted.

　　Circuit Analysis:

　　(1) Circuit structure: There are four types of circuit structures for mobile phone local oscillators:

　　a) Composed of a frequency synthesis integrated block, receive voltage-controlled oscillator (RX-VCO), 13M reference clock, preset frequency reference data (SYN-DAT; SYN-CLK; SYN-RST; SIN-EN), composed of (early mobile phones were widely used; as shown below).

　　b) Integrate the frequency synthesis block into the IF and combine with an external RX-VCO to form a multi-functional system (multi-purpose for mid-cycle and Nokia machines; (See the figure below)

　　c) Integrates the frequency synthesis integrated block and the receiving voltage-controlled oscillator (RX-VCO) into one, called the local integrated block or local oscillator licking IC (multi-purpose for mid-term and Samsung devices; as shown below).

　　d) Integrate the frequency synthesis integrated block and the receive voltage-controlled oscillator (RX-VCO) into the IF (versatile for new and generic models; as shown below).

　　It is worth noting: regardless of the structural pattern used, the frequency of generation differs; Its working principle, the direction and function of the generated frequency signals are the same.

　　Applications of RF circuits

　　RF (Radio Frequency) technology is widely used in various fields, such as television, radio, mobile phones, radar, automatic identification systems, and more. The technical term RFID (Radio Frequency Identification) refers to the use of RFID signals to identify target objects.Applications of RFID include:

　　1. ETC (Electronic Toll)

　　2. Identification and tracking of railway locomotives and rolling stock

　　3. Container identification

　　4. Identification, authentication, and tracking of valuable items

　　5. Target management for commercial retail, healthcare, logistics services, and more

　　6. Access control management

　　7. Animal identification and tracking