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The principle and application of radio frequency circuit

  • Categories:News Center
  • Time of issue:2021-01-25 10:58
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(Summary description)Radio frequency is abbreviated as RF, radio frequency is radio frequency current , which is an abbreviation of high-frequency alternating electromagnetic waves. The alternating current that changes less than 1000 times per second is called low-frequency current, and the alternating current that changes more than 1000 times is called high-frequency current. Radio frequency is such a high-frequency current.

The principle and application of radio frequency circuit

(Summary description)Radio frequency is abbreviated as RF, radio frequency is radio frequency current , which is an abbreviation of high-frequency alternating electromagnetic waves. The alternating current that changes less than 1000 times per second is called low-frequency current, and the alternating current that changes more than 1000 times is called high-frequency current. Radio frequency is such a high-frequency current.

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  • Time of issue:2021-01-25 10:58
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Radio frequency is abbreviated as RF, radio frequency is radio frequency current , which is an abbreviation of high-frequency alternating electromagnetic waves. The alternating current that changes less than 1000 times per second is called low-frequency current, and the alternating current that changes more than 1000 times is called high-frequency current. Radio frequency is such a high-frequency current.

A radio frequency circuit refers to a circuit whose electromagnetic wavelength and the size of the circuit or device are in the same order of magnitude. At this time, due to the relationship between the size of the device and the size of the wire, the circuit needs to be dealt with by the related theory of distributed parameters. This kind of circuit can be considered as a radio frequency circuit without strict requirements on its frequency, such as long-distance transmission AC power lines (50 or 60Hz) Sometimes the related theory of RF is also used to deal with. 
RF circuit block diagram


Principle of radio frequency circuit

The principle of the radio frequency circuit is introduced in detail with the radio frequency circuit of an ordinary mobile phone:

1. The structure and working principle of the receiving circuit:

When receiving, the antenna converts the electromagnetic wave sent from the base station into a weak AC current signal, filtered, amplified by high frequency, and sent to the intermediate frequency for demodulation to obtain the received 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 is composed of antenna, antenna switch, filter , high amplifier tube (low noise amplifier ), intermediate frequency integrated block (receiving demodulator) and other circuits. Early mobile phones had primary and secondary mixing circuits, whose purpose was to demodulate after lowering the receiving frequency (as shown in the figure below).

Block diagram of receiving circuit

2. The structure and working principle of the transmitting circuit

When transmitting, the transmission baseband information processed by the logic circuit is modulated into the transmission intermediate frequency, and the frequency of the transmission intermediate frequency signal is changed to 890M-915M (GSM) frequency signal with TX-VCO. After being amplified by the power amplifier, the antenna is converted into electromagnetic wave radiation.

circuit analysis:

(1) Circuit structure.

The transmitting circuit is composed of a transmitting modulator and a transmitting phase detector inside the intermediate frequency; a transmitting voltage-controlled oscillator (TX-VCO), a power amplifier (power amplifier), a power controller (power control), a transmitting transformer and other circuits. (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; they are sent into the IF, and the received signal is demodulated when receiving; when transmitting Transmit baseband information for modulation and transmit phase discrimination.

circuit analysis:

(1) Circuit structure: The mobile phone local oscillator circuit has four circuit structures:

a) Composed of frequency synthesis integrated block, receiving voltage controlled oscillator (RX-VCO), 13M reference clock , preset frequency reference data (SYN-DAT; SYN-CLK; SYN- RS T; SIN-EN), composed (early Multi-purpose mobile phone; as shown below).


b) Integrate the frequency synthesis integrated block into the IF, combined with an external RX-VCO (multi-purpose for mid-term phones and Nokia phones; (as shown below)


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

d) Integrate the frequency synthesis integrated block and the receiving voltage-controlled oscillator (RX-VCO) into the intermediate frequency (new models and unbranded models are multi-purpose; as shown below).


It is worth noting that no matter which structure mode is adopted, only the generated frequency is different; its working principle, the direction and function of the generated frequency signal are the same.

Application of radio frequency circuit

RF ( Radi o Frequency) technology is widely used in many fields, such as: TV, radio, mobile phone, radar, automatic identification system, etc. The special term RFID (Radio Frequency Identification) refers to the use of radio frequency identification signals to identify targets. RFID applications include:

 
1. ETC (Electronic Toll Collection)

2. Recognition and tracking of railway rolling stock

3. Container identification

4. Identification, certification and tracking of valuables

5. Target management of commercial retail, medical care, logistics services, etc.

6. Access prohibition management

7. Animal identification and tracking

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