At present, electronic equipment continues to rely on printed circuit boards (PCBs) as the primary method for assembling various devices and systems. Experience has shown that even when the circuit schematic is correct, improper PCB design can negatively impact the reliability of the electronic equipment. For instance, when two thin parallel traces on the PCB are placed too closely together, it can lead to signal waveform delays and the creation of reflection noise at the end of the transmission line. Therefore, it is crucial to apply the proper design techniques when creating a printed circuit board.
1. Ground wire design
In electronic devices, grounding is a crucial method for controlling interference. When grounding and shielding are properly combined, most interference issues can be effectively mitigated. The ground system of electronic equipment typically includes system ground, chassis ground (shield ground), digital ground (logic ground), and analog ground. The following points should be considered when designing the ground layout:
1. **Choose Between Single-Point and Multi-Point Grounding**
In low-frequency PCB circuits, where the signal frequency is below 1 MHz, the effects of wiring and inductance between devices are minimal, and the circulating current in the ground system has a more significant impact on interference. Therefore, single-point grounding is preferred. When the signal frequency exceeds 10 MHz, the impedance of the ground wire becomes quite high. In this case, the ground impedance should be minimized, and multiple grounding points should be used as close to each other as possible. For frequencies between 1 MHz and 10 MHz, if single-point grounding is used, the length of the ground wire should not exceed 1/20th of the wavelength; otherwise, multi-point grounding should be considered.
2. **Separate Digital and Analog Circuits**
PCB circuits often contain both high-speed digital logic circuits and analog linear circuits. These should be kept as separate as possible, with the ground connections of each circuit isolated from one another, and connected directly to the power supply ground. Efforts should be made to increase the grounding area for the analog circuits to minimize noise interference.
3. **Make the Ground Wire as Thick as Possible**
If the ground wire is too thin, changes in current can cause fluctuations in the ground potential, which in turn leads to instability in timing signals and degraded noise immunity. Therefore, ground wires should be as thick as possible to handle the required current. Ideally, the width of the ground wire should exceed 3 mm to ensure proper current handling and to reduce potential voltage drops.
4. **Create a Closed Ground Loop**
When designing the grounding system for a PCB consisting solely of digital circuits, forming the ground wire into a closed loop can significantly improve noise immunity. This is particularly important in designs with multiple integrated circuits, especially those with high power consumption. Due to the limited thickness of the ground wire, large potential differences can arise at ground junctions, weakening the noise immunity. By forming the ground layout into a loop, potential differences are minimized, thereby enhancing the overall noise resistance of the device.
1. Ground wire design
In electronic devices, grounding is a crucial method for controlling interference. When grounding and shielding are properly combined, most interference issues can be effectively mitigated. The ground system of electronic equipment typically includes system ground, chassis ground (shield ground), digital ground (logic ground), and analog ground. The following points should be considered when designing the ground layout:
1. **Choose Between Single-Point and Multi-Point Grounding**
In low-frequency PCB circuits, where the signal frequency is below 1 MHz, the effects of wiring and inductance between devices are minimal, and the circulating current in the ground system has a more significant impact on interference. Therefore, single-point grounding is preferred. When the signal frequency exceeds 10 MHz, the impedance of the ground wire becomes quite high. In this case, the ground impedance should be minimized, and multiple grounding points should be used as close to each other as possible. For frequencies between 1 MHz and 10 MHz, if single-point grounding is used, the length of the ground wire should not exceed 1/20th of the wavelength; otherwise, multi-point grounding should be considered.
2. **Separate Digital and Analog Circuits**
PCB circuits often contain both high-speed digital logic circuits and analog linear circuits. These should be kept as separate as possible, with the ground connections of each circuit isolated from one another, and connected directly to the power supply ground. Efforts should be made to increase the grounding area for the analog circuits to minimize noise interference.
3. **Make the Ground Wire as Thick as Possible**
If the ground wire is too thin, changes in current can cause fluctuations in the ground potential, which in turn leads to instability in timing signals and degraded noise immunity. Therefore, ground wires should be as thick as possible to handle the required current. Ideally, the width of the ground wire should exceed 3 mm to ensure proper current handling and to reduce potential voltage drops.
4. **Create a Closed Ground Loop**
When designing the grounding system for a PCB consisting solely of digital circuits, forming the ground wire into a closed loop can significantly improve noise immunity. This is particularly important in designs with multiple integrated circuits, especially those with high power consumption. Due to the limited thickness of the ground wire, large potential differences can arise at ground junctions, weakening the noise immunity. By forming the ground layout into a loop, potential differences are minimized, thereby enhancing the overall noise resistance of the device.
