Radio frequency is abbreviated RF, radio frequency is radio frequency current, it is a kind of abbreviation of high-frequency exchange change electromagnetic wave. ACs that change less than 1000 times per second are called low-frequency currents, and those that are greater than 1000 times are called high-frequency currents, and RF is such a high-frequency current.
A radio frequency circuit is a circuit in which the electromagnetic wavelength of the processed signal is in the same order of magnitude as the size of the circuit or device. At this time, due to the relationship between device size and wire size, the circuit needs to be dealt with by related theory of distributed parameters. Such circuits can all be considered as RF circuits, and there are no strict requirements on their frequency, such as long-distance transmission of AC power lines (50 or 60 Hz) is sometimes treated with RF related theory.
RF circuit block diagram
Principles of RF Circuits We introduce the details of ordinary mobile phone RF circuits:
1, the receiving circuit structure and working principle:
During reception, the antenna transmits the electromagnetic wave to the weak AC current signal sent by the base station and is filtered. After high-frequency amplification, it is sent to the IF for demodulation to obtain the received baseband information (RXI-P, RXI-N, RXQ-P, RXQ- N); sent to the logic audio circuit for further processing.
circuit analysis:
(1) Circuit structure
The receiving circuit is composed of an antenna, an antenna switch, a filter, a high-emission tube (low-noise amplifier), an intermediate-frequency integrated block (receiver demodulator), and the like. Earlier mobile phones had primary and secondary mixer circuits, and their purpose was to demodulate the receiver frequency (see below).
Receiver circuit block diagram
2, the structure and working principle of the transmitting circuit
During transmission, the transmit baseband information modulated by the logic circuit is modulated into the transmit intermediate frequency, and the TX-VCO is used to convert the transmit intermediate frequency signal frequency to a frequency signal of 890M-915M (GSM). After being amplified by the amplifier, the antenna is turned into electromagnetic radiation.
circuit analysis:
(1) Circuit structure.
The transmitting circuit is composed of an internal frequency transmit modulator, a transmitter phase detector, a transmit voltage-controlled oscillator (TX-VCO), a power amplifier (power amplifier), a power controller (power control), and a transmitter transformer. (As shown below)
3, the structure and working principle of the local oscillator circuit : (Local oscillator circuit, phase-locked loop circuit, frequency synthesis circuit)
The circuit generates four local oscillator frequency signals (GSM-RX; GSM-TX; DCS-RX; DCS-TX) without any information; it is sent to the internal frequency and demodulates the received signals when received; Baseband information is modulated and transmitted for phase discrimination.
circuit analysis:
(1) Circuit Structure: There are four kinds of circuit structures in the cell phone local oscillator circuit:
a) Composed of a frequency synthesis block, a receive voltage controlled oscillator (RX-VCO), a 13M reference clock, and preset frequency reference data (SYN-DAT; SYN-CLK; SYN-RST; SIN-EN) (early cell phones) Use more; as shown below).
b) Integrate the frequency synthesizing integrated block into the internal frequency, combining the external RX-VCO (Mid-term machine, Nokia machine use; (below)
c) Integrated frequency synthesis block and receiving voltage controlled oscillator (RX-VCO), called local oscillator block or local oscillator IC (intermediate machine, Samsung machine use; as shown below).
d) Integrated frequency synthesis block and receiving voltage controlled oscillator (RX-VCO) inside the IF (new type, multi-purpose machine use; as shown below).
It is worth noting that no matter what structural mode is adopted, only the generated frequency is different; its working principle and the direction and effect of the generated frequency signal are the same.
Application of RF CircuitsRF (Radio Frequency) technology is widely used in various fields, such as: television, radio, mobile phones, radar, automatic identification systems. The special term RFID (Radio Frequency Identification) refers to the use of radio frequency identification signals to identify objects. RFID applications include:
1. ETC (electronic charging)
2. Railway Locomotive and Vehicle Identification and Tracking
3, container identification
4, identification, certification and tracking of valuables
5. Target management of commercial retail, healthcare, logistics, etc.
6, out of the entrance management
7, animal identification, tracking
8, the vehicle automatically locks (theft)
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