Digital PCB design interference considered

In the design of electronic systems, in order to avoid detours and save time, you should take full account of and meet the requirements of the anti-jamming, to avoid the anti-jamming circuit board design is complete and then to carry out remedial measures. There are three basic elements to the formation of interference:
    
1, the source of interference, the interference components, equipment or signal, described as follows: du / dt, di / dt is the source of interference in mathematical language.
Such as: lightning, relays, SCR, motors, high frequency clock and so may become a source of interference.
    
2, propagation path, the interference from sources of interference pathway spread to sensitive devices or media.
The typical interference propagation path through the wire conduction and space radiation.
    
Sensitive devices, means easy to interference with the object.
Such as: the A / D, D, / A converter, microcontroller, digital ICs, the weak signal amplifier.
Anti-jamming design of the basic principle is: the sources of interference suppression, cutting off the interference propagation path, and to improve anti-interference performance of sensitive devices.

First, sources of interference suppression

Suppress the interference source as much as possible to reduce the sources of interference du / dt, di / dt. This is a top priority in anti-jamming design and most important principle, often play a multiplier effect. Reduce the sources of interference, such as the du / dt through the shunt capacitors at the both ends of the source of interference.
Reduce the sources of interference, such as the di / dt is the interference source circuit series inductance or resistance and to increase the freewheeling diode.

Suppression of interference sources commonly used measures are as follows:

    1, the relay coil increases the freewheeling diode, eliminate the interference of the back electromotive force generated in the coil is disconnected.
Only increase the freewheeling diode relay will disconnect the time lag relay action more per unit of time the number of times in the addition of Zener diode.
    
2, at both ends of the relay contacts and received a spark suppression circuit (typically an RC series circuit, resistance to the general election a few K to dozens of K capacitance choose 0.01uF), reducing the spark impact.
    
3, and filter circuit to the motor, pay attention to capacitance, inductance leads as short as possible.
    Each IC, the circuit board and connect a 0.01μF ~ 0.1μF high frequency capacitance to reduce the impact of the IC power supply.
Attention to the high-frequency capacitance of the wiring connections should be near the end of the power and stubby as far as possible, otherwise, equivalent to increasing the capacitor equivalent series resistance, it will affect the filtering effect.
    
5 wiring to avoid the 90 degree line, reducing the emission of high frequency noise.
    
6 SCR at both ends and then RC suppression circuit, reducing the noise generated by SCR (the noise a serious will thyristor breakdown).

Interference propagation path can be divided into two types of conducted interference and radiated interference.
The so-called conducted interference is spread through the wires to the interference of sensitive devices. The high-frequency interference noise and useful signal band, the increase in the wire filter to cut off the spread of high-frequency interference noise, and sometimes can be added to the isolation optocoupler. Power supply noise hazards, paying particular attention to handling. The so-called radiation interference refers to interference by space radiation spread to sensitive devices.
The general solution is to increase the distance of the source of interference with sensitive devices, land line them isolated and in sensitive devices on the drain cover.

Unplug the commonly used measures to interfere with the propagation path is as follows:

    
1, give full consideration to the impact of the power of the microcontroller. The power supply well, the anti-interference of the entire circuit to solve a half. Many single-chip power supply noise is very sensitive to give single-chip power supply of the filter circuit or regulator, the microcontroller to reduce power supply noise interference.
For example, you can use a ferrite bead and capacitor form a π-filter circuit, of course, when conditions do not ask also available 100Ω resistor instead of beads.
    2, if the microcontroller I / O port to control motors and other noise devices, isolation between the I / O port and the noise source should be added (an increase of the π-filter circuit).
Control motors and other noise devices, isolation between the I / O port and the noise source should be added (an increase of π-filter circuit).
    3, note that the crystal wiring. Crystal and microcontroller pins as close as possible to the land line to clock isolation, crystal housing grounded and fixed.
These measures will help to solve many difficult problems.
    4, a reasonable partition of the circuit board, such as strong, weak signal, digital and analog signals.
Stay away from as much as possible sources of interference (such as motors, relays) and sensitive components (eg, SCM).
    , Land line isolation of the digital area and analog, digital to analog ground to be separated, and finally at a point connected to the power ground.
A / D and D / A chip wiring as a principle, manufacturers allocated the A / D, D / A chip pinout has to consider this request.
    6, the ground of the microcontroller and high power devices should be earthed separately in order to reduce mutual interference.
The high-power devices as possible on the edge of the board.
    7, in the key areas of microcontroller I / O port, power cord, circuit board connection lines using the anti-interference components such as beads, magnetic, power filter, shield, can significantly improve anti-interference performance of the circuit.