Detailed Understanding of High Frequency Communication Circuits and High Frequency Circuit Designs

High-frequency circuits are used in a wide range of applications such as communications, broadcasting, medical equipment, lasers, and microwave systems. The changing physical characteristics of high-frequency circuit components require different processing strategies compared to low-frequency circuits. When designing high-frequency communication circuits, attention must be paid to signal integrity, electromagnetic compatibility, and wiring rules to ensure signal integrity and reduce electromagnetic interference. Performance, gain, passband, selectivity, noise figure and stability are essential for circuit optimization. With the development of communication technology, high-frequency circuits tend to be higher frequency and faster speed. In PCB manufacturing, layout, layer stacking, material selection, impedance control and grounding techniques are key to ensuring stable circuit operation.

What are high frequency communication circuits?

High-frequency communication circuits are electronic circuits used to process high-frequency signals, and these circuits are widely used in wireless communications, radar, satellite communications, television broadcasting, and radio frequency identification (RFID).

1. Frequency range: High frequency usually refers to the frequency range from a few hundred kilohertz to hundreds of gigahertz. In this range, the characteristics of electromagnetic waves begin to appear, and the traditional DC circuit theory is no longer applicable.
2. Signal Processing: High-frequency communication circuits are used for the transmission, reception, modulation, demodulation, and amplification of radio waves. These circuits require special design and technical means when dealing with high-frequency signals.
3. Electronic devices: high-frequency electronic devices are electronic components that work in the high-frequency range, and these devices play an important role in high-frequency circuits such as transmission, amplification, modulation, demodulation, and frequency synthesis, such as transistors, field effect tubes, and microwave filters.
4. Application areas: high-frequency communication circuits play an important role in mobile communications, satellite communications, wireless LANs and other communication systems, they are used for modulation and demodulation, amplification, filtering, FM and demodulation and other signal processing functions.
5. Design Principles: The design of high-frequency circuits requires consideration of bandwidth and frequency response. Bandwidth refers to the range of frequencies that can pass through a high-frequency circuit, while frequency response describes the gain or attenuation characteristics of a circuit for signals of different frequencies.
6. Performance metrics: Performance metrics for high frequency circuits include gain, passband, selectivity, noise figure and stability.

What are the characteristics of high frequency communication circuits?

High-frequency communication circuit features include high-frequency operation, component nonlinearity, significant influence of distribution parameters, functional integration, digitalization trends, efficient compact design, multi-point grounding, as well as higher requirements for stability and performance.

1. High operating frequency: High-frequency communication circuits typically operate at frequencies ranging from tens of megahertz (MHz) to hundreds of gigahertz (GHz), which allows them to handle high-speed data transmission and signal processing tasks.
2. Nonlinearities in components: At high frequencies, components in circuits such as diodes and transistors exhibit nonlinear characteristics, which leads to the creation of new frequency components such as harmonics and mixing.
3. Influence of Distribution Parameters: As the operating frequency increases, the influence of the distribution parameters in the circuit (such as inductance, capacitance, and resistance) becomes more significant, which places higher demands on the circuit design.
4. Variety of circuits: High-frequency circuits include many types, such as resonant amplifiers, power amplifiers, modems, etc., which play different roles in communication systems.
5. Monolithicization of integrated circuits: high-frequency integrated circuits tend to integrate a variety of functions on a single chip, such as A/D, D/A and RF circuits.
6. Digitalization trend: high-frequency integrated circuits are gradually digitalized, based on software radio technology to control different parameters of each module of the wireless communication system to achieve different functions.
7. High-efficiency conversion: Compared with the traditional linear regulated power supply, high-frequency switching power supply has a higher conversion efficiency, thanks to its use of switching components for periodic switching to reduce energy loss.
8. Small volume design: due to the higher operating frequency, high-frequency switching power supply can use smaller inductors and transformers, thus reducing the volume of the whole power supply system.
9. Multi-point grounding principle: In order to reduce the impedance of the ground line and its reduction of stray inductance and distributed capacitance between the ground line caused by mutual coupling between the circuits, high-frequency circuits using the nearest ground, i.e., the principle of multi-point grounding.
10. Stability requirements: the stability of the high-frequency amplifier circuit refers to the working state or conditions change, the degree of stability of its main performance, such as changes in ambient temperature or power supply voltage fluctuations.

Application scenarios of high-frequency communication circuits

High-frequency communication circuits are widely used in communication systems, broadcasting and television, medical equipment, radar, laser, RFID, environmental monitoring, scientific research and 5G technology to support signal processing, wireless communication and high-frequency control functions.

1. Communication systems: High-frequency circuits play an important role in communication systems such as mobile communications, satellite communications, and wireless LANs, and are used for signal processing functions such as modulation and demodulation, amplification, filtering, FM and demodulation.
2. Radio and TV: Radio and TV stations use HF circuits to transmit and receive broadcast signals, including antennas, transmitters and receivers.
3. Medical Equipment: High-frequency circuits in medical equipment such as MRIs, CT scanners and ultrasound equipment are used to generate and process medical images.
4. Laser and Microwave Systems: Laser and microwave systems require high-frequency circuits to generate and control laser or microwave signals for applications such as communications, range-finding, and radar.
5. Radio Control: Remote controls, garage door openers, smart home devices, etc. utilize high-frequency circuits for wireless communication and remote control.
6. Radio Frequency Identification (RFID): RFID technology uses high-frequency circuits for applications such as item tracking, inventory management, and access control systems.
7. Radar Systems: Radar systems use high-frequency circuits to transmit and receive radar waves for aircraft navigation, weather forecasting and military applications.
8. Environmental Monitoring: High frequency circuits are used in environmental monitoring systems such as weather radar, earthquake detection and air quality monitoring.
9. Scientific research: HF circuits in scientific laboratories are used for experiments and measurements in fields such as physics, chemistry and biology.
10. 5G communication: In 5G technology, high-frequency band communication belongs to the eMBB scenario, which mainly undertakes hotspot high-speed transmission, and can be subdivided into a variety of networking scenarios such as high-frequency isolated cellular networking, high-frequency continuous coverage cellular same-frequency networking, high-frequency continuous coverage cellular heterogeneous frequency networking, ultra-dense area cellular networking, indoor high-capacity networking, and outdoor-to-indoor coverage.

High-frequency communication circuit design guidelines

The design of high-frequency communication circuits needs to focus on the selection of functional solutions, component parameter calculation, impedance matching, layout and packaging, distribution parameter effects, stability and simulation optimization to ensure that the bandwidth and frequency response meet the performance requirements.

1. Selection of the overall realization of the program: according to the circuit function and performance indicators, to determine the composition of the circuit.
2. Selection of unit circuit form: Determine the form of each unit circuit in the overall realization scheme.
3. Calculation of circuit parameters: Calculate the values of each component that makes up the circuit.
4. Component selection: In addition to the calculated parameter values, cost, ease of purchase, and existing conditions are considered.
5. Bandwidth and Frequency Response: Bandwidth and frequency response need to be considered in the design to ensure the quality of signal transmission and processing.
6. Transmission Line and Impedance Matching: In high frequency circuits, it is critical to match the characteristic impedance of the transmission line to minimize signal reflection and distortion.
7. Packaging and Layout: Packaging requires that interconnections between circuit components be as short as possible to minimize inductance and capacitance in the signal path. Layout needs to avoid sources of interference and reduce crosstalk and electromagnetic radiation.
8. Stability and Reliability: Consider the effects of temperature changes, power supply fluctuations and device aging on circuit performance, and take appropriate measures to ensure circuit stability and reliability.
9. Consideration of Distribution Parameters: When the frequency of the electrical signal is greater than 100MHz, the distribution parameters of the circuit must be considered, at which point the circuit is no longer modeled as a lumped parameter.
10. Additional capacitance and inductance of components: In high-frequency circuits, commonly used components such as resistors and capacitors should not only be considered in terms of their originally established single component parameters, but also in terms of the additional capacitance and inductance brought about by their manufacturing principle.
11. Use of Microstrip and Ribbon Wire Components: When frequencies are as high as 100 megabits or even several gigabits, the use of microstrip and ribbon wire components, which are composed purely of circuit board copper foil, demonstrates the necessity of their use.
12. PCB design: Design a PCB stack structure that supports larger layer capacitances, for example a six layer stack might contain a top signal layer, a first ground layer, a first power layer, a second power layer, a second ground layer and a bottom signal layer.
13. High-frequency layer capacitance: If the power supply layer must be split and there are multiple VDD power rails on the same layer, the largest possible power supply layer should be used. Do not leave voids, and attention should be paid to sensitive circuits, which will maximize the capacitance of that VDD layer.
14. Circuit Simulation: After completing the circuit design, you can use computer-aided analysis software (e.g., Pspice) to simulate the circuit and make preliminary adjustments.

How should a high frequency communication circuit PCB be manufactured?

The manufacturing of HF communication circuit PCBs is a complex and delicate process that involves several key aspects. Here are some important manufacturing processes and points:

1. Material Selection and Pretreatment:

   • The materials used for HF PCB circuit boards must have low dielectric constants, low dielectric loss coefficients and stable dielectric properties. Commonly used materials include polytetrafluoroethylene (PTFE), thermosetting resins and ceramic materials.
   • During the material pretreatment stage, the temperature and humidity of the environment should be strictly controlled to avoid material deformation or moisture, which may affect the accuracy of subsequent processing.

2. Lamination process:

   • Lamination design is the first step in the manufacture of high-frequency PCBs. Designers need to determine the number of layers of the board, the choice of materials and the thickness of each layer according to the functional requirements of the circuit and electromagnetic compatibility considerations.
   • During the lamination process, a series of operations such as punching, plating, and graphic transfer need to be performed by precision machinery to form the desired circuit pattern.

3. Graphics transfer technology:

   • High-precision light painting and exposure technologies are used to ensure the accuracy of the circuit pattern. For high-density or ultra-fine line designs, consider using laser direct writing technology to improve accuracy.

4. Etching process optimization:

   • The etching process needs to control the solution concentration, temperature and spray pressure and other parameters to achieve the ideal effect of vertical sidewalls and no side etching.
   • The use of pulse etching or wet film etching technology can further improve the accuracy.

5. Copper plating process:

   • Copper plating is a critical step in the metallization of the board after the laminate design is complete.
   • This process usually includes both electrolytic and chemical copper plating.
   • The uniformity and surface finish of the copper plating is especially important to avoid signal distortion and insertion loss.

6. Press-fit process:

   • The press-fit process is a critical step in the manufacture of multilayer PCBs and requires precise control of the thickness and alignment of each layer.

7. Anti-interference treatment:

   • The use of metal shielding, anti-static treatment and other ways to improve the anti-interference ability of the circuit board.

8. Surface treatment:

   • The use of chemical treatment and physical treatment and other processes to ensure the quality of the circuit board, improve the surface corrosion resistance and adhesion.

9. Testing and Quality Control:

   • After the production of HF PCB boards is completed, rigorous testing is required, including electrical testing, impedance testing, and environmental simulation testing to ensure that each board meets design specifications and performance requirements.

10. Precise Processing:

    • The manufacturing of high frequency PCB boards requires extreme precision.
    • The production process requires the use of high-precision mechanical equipment and fine operating techniques to ensure that the size and shape of the circuit meets the design requirements.

11. Material Handling:

    • In order to obtain the best electrical performance, the production requires special treatment of the substrate material, such as baking, cleaning and surface treatment, etc., in order to eliminate the stress and moisture inside the material and to ensure the flatness and stability of the material.

12. Plating process:

    • The uniformity and adhesion of the plating layer is critical to the performance of high frequency circuits. The composition, temperature and current density of the plating solution should be strictly controlled during the production process to ensure the quality of the plating layer.

Frequently Asked Questions

1. What is a high frequency circuit? High-frequency circuits are electronic circuits that operate in the range of electromagnetic signals with higher operating frequencies, usually used to process radio frequency (RF) signals, microwave signals, or higher-frequency electromagnetic waves. Its main applications include wireless communications, radar, satellites, and radio frequency identification (RFID). Characteristics of high-frequency circuits include:

   • Higher frequencies, typically in the range of 3 MHz to 300 GHz.
   • Circuit components may exhibit different characteristics than at lower frequencies, such as parasitic capacitance and inductance, which have a more pronounced effect on performance.
   • Special attention needs to be paid to impedance matching, signal integrity and electromagnetic interference issues.

2. What is high frequency communication? High-frequency communication is a communication technology that utilizes high-frequency electromagnetic waves for information transfer. According to the definition of electromagnetic wave frequency range, HF communication can cover shortwave (HF, 3-30 MHz), very high frequency (VHF, 30-300 MHz), ultra-high frequency (UHF, 300 MHz-3 GHz), and even higher microwave and millimeter wave communication. Key features:

   • HF signals can transmit large amounts of data (e.g., television, cellular networks).
   • The HF band is susceptible to attenuation and interference, and transmission distances are limited, often requiring relay or directional transmission.
   • HF communications are widely used in radio broadcasting, satellite communications, Wi-Fi, 5G and other scenarios.

3. What is the highest frequency electrical signal? The highest known frequency electrical signals depend on the limits of generation and detection techniques. Here are some common upper frequency limits:

   • In practice, the THz (terahertz) band (0.1-10 THz) is the higher range of electrical signals and has been used for research and communication experiments.
   • The optical band (above 1012^{12}12 Hz): frequencies up to hundreds of THz can be found in laser or optical communications. In laboratory research, UHF electromagnetic signals (e.g., X-rays or gamma rays) can exceed hundreds of PHz but are not used for conventional electrical signal communications.

4. What is the high frequency range? According to the International Radiocommunication Standards (IRS), the frequency range of HF electromagnetic waves is as follows:

   • High Frequency (HF): 3 MHz - 30 MHz
   • Very High Frequency (VHF): 30 MHz - 300 MHz
   • Ultra High Frequency (UHF): 300 MHz - 3 GHz
   • Microwave: 3 GHz - 300 GHz

5. What is the HF frequency range?

   • In the field of wireless communications: typically high frequency (HF) and above, ranging from 3 MHz to hundreds of GHz.
   • Circuit design: HF circuits typically range from a few tens of MHz to tens of GHz, e.g., a 1 GHz circuit design is often considered “high frequency.

6. How do I design a high-frequency circuit? High frequency circuit design requires special attention to the following issues:

   1. Impedance matching:

      • Use a Smith Chart to design the impedance match of the transmission line.
      • Ensure that the input and output impedances match the impedance of the circuit or antenna to minimize signal reflection.

   2. Electromagnetic Interference (EMI) and Electromagnetic Compatibility (EMC):

      • Avoid parasitic effects: At high frequencies, wires, solder joints and even packages form parasitic inductance and parasitic capacitance.
      • Add shielding or filters to suppress interference.

   3. Transmission line design:

      • At high frequencies, the transmission behavior of signals across the board is significantly affected by distributed parameters such as propagation delay and loss.
      • Use techniques such as microstrip lines and striplines to minimize signal loss.

   4. Circuit component selection:

      • Use high-frequency-specific components (e.g., high-frequency capacitors, high-speed transistors).
      • Ensure that the frequency response of the device covers the target operating frequency.

   5. Simulation and optimization:

      • Perform circuit and EM simulations with the help of tools (e.g. ADS, HFSS).

7. How does high frequency communication work in airplanes? Aircraft communications utilize a variety of high-frequency bands and communication technologies, including:

   1. Shortwave communications (HF):

      • Uses the shortwave band (3-30 MHz) for long distance communications.
      • The ionospheric reflective properties of shortwave are used to maintain contact with ground control centers.

   2. Very High Frequency Communications (VHF):

      • With a frequency range of 118 MHz - 137 MHz, it is the main frequency band for aviation communications.
      • It is used for inter-aircraft communications and command exchanges with ground towers.

   3. Satellite Communications:

      • Uses microwave bands (e.g. Ku-band, Ka-band) to connect aircraft and satellites for real-time transmission of flight data, Internet services, etc.

   4. Wi-Fi and Entertainment Communications:

      • Uses 2.4 GHz and 5 GHz Wi-Fi technology to provide passengers with in-flight Internet access.