In PCB design for electronic systems, to avoid unnecessary detours and save time, it is essential to thoroughly consider and address anti-interference requirements upfront, rather than relying on remedial measures after the PCB design is complete. There are three primary elements that contribute to interference:
1. **Interference Source**: This refers to the component, device, or signal that generates interference. Mathematically, this is represented as du/dt, where high di/dt values indicate the interference source. Examples of interference sources include lightning, relays, thyristors, motors, high-frequency clocks, and more.
2. **Propagation Path**: This refers to the medium or route through which the interference travels from the source to sensitive devices. Typical propagation paths include conduction through wires and radiation through space.
3. **Sensitive Devices**: These are the components that are vulnerable to interference, such as A/D and D/A converters, microcontrollers, digital ICs, weak-signal amplifiers, etc.
The fundamental principles of anti-interference PCB layout design are:
– Suppressing interference sources
– Interrupting interference propagation paths
– Enhancing the resistance of sensitive devices to interference (similar to preventing the spread of infectious diseases).
### 1. Suppressing Interference Sources
Suppressing the interference source aims to reduce the du/dt and di/dt of the source as much as possible. This is the highest priority and the most crucial principle in anti-interference PCB design, often yielding significant results with relatively little effort. To reduce du/dt, capacitors are typically connected in parallel at both ends of the interference source. Reducing di/dt is done by adding inductance or resistance in series with the interference loop, as well as incorporating a freewheeling diode.
Common measures to suppress interference sources include:
1. **Relay Coils**: Adding a freewheeling diode across the relay coil helps eliminate interference caused by the back electromotive force when the coil is de-energized. Simply adding a freewheeling diode will delay the relay’s turn-off time. However, incorporating a Zener diode allows the relay to operate more frequently within the same period.
2. **Spark Suppression**: A spark suppression circuit, typically an RC series circuit (with resistance usually ranging from a few kΩ to tens of kΩ, and a capacitor value around 0.01μF), should be connected in parallel across the relay contacts to minimize the impact of electric sparks.
3. **Motor Filtering**: A filter circuit should be added to the motor, ensuring that the leads to the capacitor and inductance are as short as possible to optimize performance.
4. **ICs on the PCB**: Each IC on the PCB should be paired with a 0.01μF to 0.1μF high-frequency capacitor in parallel to reduce the impact on the power supply. Care should be taken to route the capacitor traces as close as possible to the power supply pins and keep them short. Otherwise, the capacitor’s equivalent series resistance may increase, diminishing its filtering effectiveness.
5. **Avoid 90-Degree Bends**: Avoid 90-degree bends in the routing of signal traces to reduce high-frequency noise emissions.
6. **Thyristors**: For thyristors, an RC suppression circuit should be connected in parallel at both ends to reduce the noise they generate. This noise can potentially cause the thyristor to break down.
Interference can be further categorized based on its propagation path, either as **conducted interference** or **radiated interference**.
The term “conducted interference” refers to interference that propagates to sensitive devices through wires. High-frequency interference noise and useful signals typically operate within different frequency bands. The propagation of high-frequency interference can be mitigated by adding a filter to the wire, and in some cases, an isolation optocoupler can also be used to address the issue. Power supply noise is particularly harmful and requires special attention during design and implementation. On the other hand, “radiated interference” refers to interference that spreads to sensitive devices via space radiation. The common solution is to increase the distance between the interference source and the sensitive device, isolate them using a ground wire, and add shielding to the sensitive device.
Common measures to block the interference propagation path include:
(1) Carefully consider the impact of the power supply on the microcontroller. If the power supply is managed effectively, the anti-interference capability of the entire circuit is significantly improved. Many microcontrollers are highly sensitive to power supply noise, so it is important to incorporate a filter circuit or voltage regulator to minimize the impact of power supply noise. For example, a π-shaped filter circuit can be formed using magnetic beads and capacitors. If the requirements are less stringent, 100Ω resistors can serve as a substitute for magnetic beads.
(2) Pay close attention to the layout of the crystal oscillator. Place the crystal oscillator as close as possible to the microcontroller pins, isolate the clock area with a ground wire, and ensure that the crystal oscillator’s case is grounded and securely fixed. This approach can resolve many challenging issues.
(3) Ensure proper segmentation of the circuit board, separating strong and weak signals, as well as digital and analog signals. It is important to keep interference sources, such as motors and relays, as far away as possible from sensitive components like microcontrollers.
(4) Use a ground wire to separate the digital area from the analog area, keeping the digital and analog grounds separate and finally connecting them to the power ground at a single point. This principle should also guide the layout of A/D and D/A chips, as manufacturers typically design pin configurations with this separation in mind.
(5) The ground wires of the microcontroller and high-power devices should be grounded independently to reduce mutual interference. Whenever possible, place high-power devices at the edges of the circuit board.
(6) The use of anti-interference components, such as magnetic beads, ferrite rings, power filters, and shields, in critical areas (e.g., microcontroller I/O ports, power lines, and board interconnections) can significantly enhance the circuit’s resistance to interference.
### Improving the Anti-Interference Performance of Sensitive Devices
Enhancing the anti-interference performance of sensitive devices involves minimizing the pickup of interference noise and ensuring that the device can recover quickly from abnormal conditions.
Common strategies to improve the anti-interference performance of sensitive devices include:
(1) Minimize the loop area when routing traces to reduce induced noise.
(2) Use thicker power and ground wires when routing. In addition to reducing voltage drops, this helps minimize coupling noise.
(3) For unused I/O ports on the microcontroller, avoid leaving them floating. Instead, connect them to either ground or the power supply. Similarly, idle terminals on other ICs should be grounded or connected to the power supply without altering the system logic.
(4) Incorporating power supply monitoring and watchdog circuits, such as the IMP809, IMP706, IMP813, X25043, and X25045, can greatly improve the anti-interference capability of the entire circuit.
(5) If speed requirements allow, reduce the clock frequency of the microcontroller and opt for lower-speed digital circuits to decrease susceptibility to noise.
(6) In PCB designs, IC devices are typically soldered directly onto the circuit board, with IC sockets rarely used.
If your have any questions about PCB ,please contact me info@wellcircuits.com
1. **Interference Source**: This refers to the component, device, or signal that generates interference. Mathematically, this is represented as du/dt, where high di/dt values indicate the interference source. Examples of interference sources include lightning, relays, thyristors, motors, high-frequency clocks, and more.
2. **Propagation Path**: This refers to the medium or route through which the interference travels from the source to sensitive devices. Typical propagation paths include conduction through wires and radiation through space.
3. **Sensitive Devices**: These are the components that are vulnerable to interference, such as A/D and D/A converters, microcontrollers, digital ICs, weak-signal amplifiers, etc.
The fundamental principles of anti-interference PCB layout design are:
– Suppressing interference sources
– Interrupting interference propagation paths
– Enhancing the resistance of sensitive devices to interference (similar to preventing the spread of infectious diseases).
### 1. Suppressing Interference Sources
Suppressing the interference source aims to reduce the du/dt and di/dt of the source as much as possible. This is the highest priority and the most crucial principle in anti-interference PCB design, often yielding significant results with relatively little effort. To reduce du/dt, capacitors are typically connected in parallel at both ends of the interference source. Reducing di/dt is done by adding inductance or resistance in series with the interference loop, as well as incorporating a freewheeling diode.
Common measures to suppress interference sources include:
1. **Relay Coils**: Adding a freewheeling diode across the relay coil helps eliminate interference caused by the back electromotive force when the coil is de-energized. Simply adding a freewheeling diode will delay the relay’s turn-off time. However, incorporating a Zener diode allows the relay to operate more frequently within the same period.
2. **Spark Suppression**: A spark suppression circuit, typically an RC series circuit (with resistance usually ranging from a few kΩ to tens of kΩ, and a capacitor value around 0.01μF), should be connected in parallel across the relay contacts to minimize the impact of electric sparks.
3. **Motor Filtering**: A filter circuit should be added to the motor, ensuring that the leads to the capacitor and inductance are as short as possible to optimize performance.
4. **ICs on the PCB**: Each IC on the PCB should be paired with a 0.01μF to 0.1μF high-frequency capacitor in parallel to reduce the impact on the power supply. Care should be taken to route the capacitor traces as close as possible to the power supply pins and keep them short. Otherwise, the capacitor’s equivalent series resistance may increase, diminishing its filtering effectiveness.
5. **Avoid 90-Degree Bends**: Avoid 90-degree bends in the routing of signal traces to reduce high-frequency noise emissions.
6. **Thyristors**: For thyristors, an RC suppression circuit should be connected in parallel at both ends to reduce the noise they generate. This noise can potentially cause the thyristor to break down.
Interference can be further categorized based on its propagation path, either as **conducted interference** or **radiated interference**.
The term “conducted interference” refers to interference that propagates to sensitive devices through wires. High-frequency interference noise and useful signals typically operate within different frequency bands. The propagation of high-frequency interference can be mitigated by adding a filter to the wire, and in some cases, an isolation optocoupler can also be used to address the issue. Power supply noise is particularly harmful and requires special attention during design and implementation. On the other hand, “radiated interference” refers to interference that spreads to sensitive devices via space radiation. The common solution is to increase the distance between the interference source and the sensitive device, isolate them using a ground wire, and add shielding to the sensitive device.
Common measures to block the interference propagation path include:
(1) Carefully consider the impact of the power supply on the microcontroller. If the power supply is managed effectively, the anti-interference capability of the entire circuit is significantly improved. Many microcontrollers are highly sensitive to power supply noise, so it is important to incorporate a filter circuit or voltage regulator to minimize the impact of power supply noise. For example, a π-shaped filter circuit can be formed using magnetic beads and capacitors. If the requirements are less stringent, 100Ω resistors can serve as a substitute for magnetic beads.
(2) Pay close attention to the layout of the crystal oscillator. Place the crystal oscillator as close as possible to the microcontroller pins, isolate the clock area with a ground wire, and ensure that the crystal oscillator’s case is grounded and securely fixed. This approach can resolve many challenging issues.
(3) Ensure proper segmentation of the circuit board, separating strong and weak signals, as well as digital and analog signals. It is important to keep interference sources, such as motors and relays, as far away as possible from sensitive components like microcontrollers.
(4) Use a ground wire to separate the digital area from the analog area, keeping the digital and analog grounds separate and finally connecting them to the power ground at a single point. This principle should also guide the layout of A/D and D/A chips, as manufacturers typically design pin configurations with this separation in mind.
(5) The ground wires of the microcontroller and high-power devices should be grounded independently to reduce mutual interference. Whenever possible, place high-power devices at the edges of the circuit board.
(6) The use of anti-interference components, such as magnetic beads, ferrite rings, power filters, and shields, in critical areas (e.g., microcontroller I/O ports, power lines, and board interconnections) can significantly enhance the circuit’s resistance to interference.
### Improving the Anti-Interference Performance of Sensitive Devices
Enhancing the anti-interference performance of sensitive devices involves minimizing the pickup of interference noise and ensuring that the device can recover quickly from abnormal conditions.
Common strategies to improve the anti-interference performance of sensitive devices include:
(1) Minimize the loop area when routing traces to reduce induced noise.
(2) Use thicker power and ground wires when routing. In addition to reducing voltage drops, this helps minimize coupling noise.
(3) For unused I/O ports on the microcontroller, avoid leaving them floating. Instead, connect them to either ground or the power supply. Similarly, idle terminals on other ICs should be grounded or connected to the power supply without altering the system logic.
(4) Incorporating power supply monitoring and watchdog circuits, such as the IMP809, IMP706, IMP813, X25043, and X25045, can greatly improve the anti-interference capability of the entire circuit.
(5) If speed requirements allow, reduce the clock frequency of the microcontroller and opt for lower-speed digital circuits to decrease susceptibility to noise.
(6) In PCB designs, IC devices are typically soldered directly onto the circuit board, with IC sockets rarely used.
If your have any questions about PCB ,please contact me info@wellcircuits.com
