1. The overall layout of printed circuit boards and device placement is crucial for the success of a product. Attention must be paid to both internal quality and overall aesthetics. A balanced and sparse arrangement of components is essential, avoiding excessive density or uneven distribution. Minimize the use of vias, and aim for a rectangular board shape with an aspect ratio of 3:2 or 4:3. Additionally, noise levels should be managed; a 4-layer board typically exhibits 20dB lower noise compared to a double-layer board, while a 6-layer board shows a further 10dB reduction. Whenever feasible, opt for multi-layer boards to enhance performance and signal integrity.
2. PCBs are typically divided into three areas: analog circuits (sensitive to interference), digital circuits (susceptible to interference and generating interference), and power drive circuits (potential sources of interference). Proper segmentation of the board into these areas is essential to minimize interference and optimize performance.
3. Select components with low power consumption and high stability, minimizing the use of high-speed devices whenever possible to reduce noise and enhance reliability.
4. Pay meticulous attention to routing: avoid unnecessarily thin traces for wide lines and ensure smooth paths for high-voltage and high-frequency lines, eliminating sharp corners and right angles. Ground traces should be wide, utilizing ample copper areas to improve connectivity.
5. External clocks pose a significant high-frequency noise source, potentially affecting both the application system and external environments, leading to electromagnetic compatibility issues. Opt for low-frequency single-chip microcontrollers to reduce system noise. Recent advancements have enabled manufacturers to reduce external clock requirements while maintaining computing speed through innovative technologies such as internal phase-locked loops.
6. Routing should follow logical directions, separating input/output, AC/DC, strong/weak signals, high/low frequencies, and high/low voltages to prevent interference. Aim for linear or separated routing paths, avoiding circular patterns whenever possible. Design requirements may vary depending on the application; however, vertical routing between layers is generally preferred, and overcrowding of components should be avoided.
7. Device placement plays a critical role in noise mitigation. Place related devices close to each other to enhance noise immunity, especially components like clock generators, crystal oscillators, and CPU clock inputs, which are prone to noise. Keep noise-sensitive, low-current, and high-current circuits segregated from logic circuits whenever feasible, and consider using separate circuit boards if necessary to minimize interference.
2. Ground wire technology SkE safety regulations and electromagnetic compatibility network
1) Analog circuits and digital circuits have many similarities and differences in the design and wiring methods of component layout diagrams. In the analog circuit, due to the existence of the amplifier, the extremely small noise voltage generated by the wiring will cause serious distortion of the output signal. In the digital circuit, the TTL noise tolerance is 0.4V ~ 0.6V, and the CMOS noise tolerance is 0.3 Vcc. ~0.45 times, so the digital circuit has strong anti-interference ability. Reasonable selection of good power supply and ground bus mode is an important guarantee for the reliable operation of the instrument. Quite a lot of interference sources are generated by power supply and ground bus, among which the noise interference caused by ground wire.
2) The digital ground is separated from the analog ground (or grounded at one point), and the ground wire is widened. The wire width should be determined according to the current. Generally speaking, the thicker the better (a 100mil wire passes through a current of about 1 to 2A). Ground wire > power wire > signal wire is a reasonable choice of wire width.
3) The power line and the ground line should be as close as possible, and the power supply and ground on the entire printed board should be distributed in a “well” shape, so that the distribution line current can be balanced.
4) In order to reduce the crosstalk between the lines, the distance between the printed lines can be increased if necessary, and some zero-volt lines are placed in it as the isolation between the lines. Especially between input and output signals, decoupling, filtering, and isolation are the three commonly used measures for hardware anti-interference.
a) Decoupling, filtering, and isolation are the three commonly used measures for hardware anti-interference.
b) The power input end is connected across an electrolytic capacitor of 10~100uF. If possible, it is better to connect more than 100uF; in principle, each integrated circuit chip should be arranged with a 0.01uF ceramic capacitor. But capacitors; for devices with weak anti-noise ability and large power changes when turned off, such as RAM and ROM storage devices, a decoupling capacitor should be directly connected between the power line and the ground line of the chip.
c) Filtering refers to classifying various types of signals according to their frequency characteristics and controlling their direction. Commonly used are various low-pass filters, high-pass filters, band-pass filters. The low-pass filter is used on the incoming AC power line to allow the 50-cycle AC power to pass smoothly, and other high-frequency noises are introduced into the ground. The configuration index of the low-pass filter is the insertion loss. The selected low-pass filter insertion loss is too low to suppress the noise, and the high insertion loss will cause “leakage” and affect the personal safety of the system. High-pass and band-pass filters should be selected and used according to the signal processing requirements in the system.
d) Typical signal isolation is optical isolation. Using optoelectronic isolation devices to isolate the input and output of the single-chip microcomputer, on the one hand, the interference signal cannot enter the single-chip microcomputer system, and on the other hand, the noise of the single-chip microcomputer system itself will not be transmitted by conduction. Shielding is used to isolate space radiation. For components with particularly large noise, such as switching power supplies, they are covered with metal boxes, which can reduce the interference of noise sources to the single-chip microcomputer system. For analog circuits that are particularly afraid of interference, such as high-sensitivity weak-signal amplifying circuits, they can be shielded. The important thing is that the metal shield itself must be connected to the real ground SkE safety regulation and electromagnetic compatibility network on the PCB board.
2. PCBs are typically divided into three areas: analog circuits (sensitive to interference), digital circuits (susceptible to interference and generating interference), and power drive circuits (potential sources of interference). Proper segmentation of the board into these areas is essential to minimize interference and optimize performance.
3. Select components with low power consumption and high stability, minimizing the use of high-speed devices whenever possible to reduce noise and enhance reliability.
4. Pay meticulous attention to routing: avoid unnecessarily thin traces for wide lines and ensure smooth paths for high-voltage and high-frequency lines, eliminating sharp corners and right angles. Ground traces should be wide, utilizing ample copper areas to improve connectivity.
5. External clocks pose a significant high-frequency noise source, potentially affecting both the application system and external environments, leading to electromagnetic compatibility issues. Opt for low-frequency single-chip microcontrollers to reduce system noise. Recent advancements have enabled manufacturers to reduce external clock requirements while maintaining computing speed through innovative technologies such as internal phase-locked loops.
6. Routing should follow logical directions, separating input/output, AC/DC, strong/weak signals, high/low frequencies, and high/low voltages to prevent interference. Aim for linear or separated routing paths, avoiding circular patterns whenever possible. Design requirements may vary depending on the application; however, vertical routing between layers is generally preferred, and overcrowding of components should be avoided.
7. Device placement plays a critical role in noise mitigation. Place related devices close to each other to enhance noise immunity, especially components like clock generators, crystal oscillators, and CPU clock inputs, which are prone to noise. Keep noise-sensitive, low-current, and high-current circuits segregated from logic circuits whenever feasible, and consider using separate circuit boards if necessary to minimize interference.
2. Ground wire technology SkE safety regulations and electromagnetic compatibility network
1) Analog circuits and digital circuits have many similarities and differences in the design and wiring methods of component layout diagrams. In the analog circuit, due to the existence of the amplifier, the extremely small noise voltage generated by the wiring will cause serious distortion of the output signal. In the digital circuit, the TTL noise tolerance is 0.4V ~ 0.6V, and the CMOS noise tolerance is 0.3 Vcc. ~0.45 times, so the digital circuit has strong anti-interference ability. Reasonable selection of good power supply and ground bus mode is an important guarantee for the reliable operation of the instrument. Quite a lot of interference sources are generated by power supply and ground bus, among which the noise interference caused by ground wire.
2) The digital ground is separated from the analog ground (or grounded at one point), and the ground wire is widened. The wire width should be determined according to the current. Generally speaking, the thicker the better (a 100mil wire passes through a current of about 1 to 2A). Ground wire > power wire > signal wire is a reasonable choice of wire width.
3) The power line and the ground line should be as close as possible, and the power supply and ground on the entire printed board should be distributed in a “well” shape, so that the distribution line current can be balanced.
4) In order to reduce the crosstalk between the lines, the distance between the printed lines can be increased if necessary, and some zero-volt lines are placed in it as the isolation between the lines. Especially between input and output signals, decoupling, filtering, and isolation are the three commonly used measures for hardware anti-interference.
a) Decoupling, filtering, and isolation are the three commonly used measures for hardware anti-interference.
b) The power input end is connected across an electrolytic capacitor of 10~100uF. If possible, it is better to connect more than 100uF; in principle, each integrated circuit chip should be arranged with a 0.01uF ceramic capacitor. But capacitors; for devices with weak anti-noise ability and large power changes when turned off, such as RAM and ROM storage devices, a decoupling capacitor should be directly connected between the power line and the ground line of the chip.
c) Filtering refers to classifying various types of signals according to their frequency characteristics and controlling their direction. Commonly used are various low-pass filters, high-pass filters, band-pass filters. The low-pass filter is used on the incoming AC power line to allow the 50-cycle AC power to pass smoothly, and other high-frequency noises are introduced into the ground. The configuration index of the low-pass filter is the insertion loss. The selected low-pass filter insertion loss is too low to suppress the noise, and the high insertion loss will cause “leakage” and affect the personal safety of the system. High-pass and band-pass filters should be selected and used according to the signal processing requirements in the system.
d) Typical signal isolation is optical isolation. Using optoelectronic isolation devices to isolate the input and output of the single-chip microcomputer, on the one hand, the interference signal cannot enter the single-chip microcomputer system, and on the other hand, the noise of the single-chip microcomputer system itself will not be transmitted by conduction. Shielding is used to isolate space radiation. For components with particularly large noise, such as switching power supplies, they are covered with metal boxes, which can reduce the interference of noise sources to the single-chip microcomputer system. For analog circuits that are particularly afraid of interference, such as high-sensitivity weak-signal amplifying circuits, they can be shielded. The important thing is that the metal shield itself must be connected to the real ground SkE safety regulation and electromagnetic compatibility network on the PCB board.
