round in double-sided board, the interference between the signals will become smaller. The reason is that the large area of ground reduces the characteristic impedance of the signal line and the signal reflection at the D-side. The characteristic impedance is inversely proportional to the square of the dielectric constant of medium from the signal line to ground, which is proportional to the natural logarithm of the thickness of the medium. If the AB line is an analog signal, for avoiding the interference of digital circuit signal line CD on line AB, the distance between them should be 2 to 3 times greater than the one from line AB and ground. Partially shielding the ground, the lead with junctions will be wired on the both sides.
Reduce the noise from the power supply
The power supply offers energy to the system and adds noise to the powered power supply. In the circuit, microcontroller reset line, interrupt line and some other control lines are most susceptible to external noise interference. The Strong interference on the power grid passes through power supply into the circuit, even if the battery itself also has high-frequency noise in the battery-powered system. Analog signal in circuits cannot withstand the interference from the power supply.
Notice the high-frequency characteristics of PCB and components
In high frequency, the lead, through-hole, resistance, capacitance, distributed inductance and capacitance of connectors cannot be ignored. Besides, distributed inductance of capacitance and distributed capacitance of inductance cannot be neglected. The resistance produces a reflection of the high frequency signal, and the distributed capacitance of the lead will work. When the length is greater than 1/20 of the corresponding wavelength of the noise frequency, the antenna effect is generated and the noise is spreading out through the lead. The through-hole in printed circuit board brings about 0.6pf of capacitance, while the encapsulated material in an integrated circuit causes 2 ~ 6pf.A connector on a circuit board has a 520nH distributed inductance. A double-stranded 24-pin integrated circuit socket leads in distributed inductance of 4 ~ 18nH.These small distribution parameters are negligible for microcontrollers in these lower frequency systems, but special attention must be paid to high speed systems.
Component layout should be in rationalization partition
The anti-electromagnetic interference should be fully considered in components placement on the PCB board, one of the principles is making the lead between the components as short as possible. In layout, the analog signal part, high-speed digital circuit part and the noise source part (such as the relay, high current switch, etc.) are reasonably separated, so that the signal coupling is the smallest.
Handle the ground wire
The power and ground wire are the most important parts for printed circuit boards. To overcome the electromagnetic interference, the main method is to ground. For double-sided board, the ground layout is special. By single-point grounding, power and ground are connected to the board from both ends of the power supply, and each of them has a junction.
The printed circuit board should have many returned ground wires, which will be gathered the junction back to the power. This is the so-called single point of grounding. The separation of analog ground, digital ground and high-power device, refers to the wiring separating and finally coming together to the ground junction. When connecting to a signal other than a printed circuit board, a shielded cable is usually used. For high frequency and digital signals, both ends of the shielded cable are grounded. The shielded cable used in low-frequency analog signal should be grounded on one end. The Circuits that are very sensitive to noise and interference or circuits or the ones with severe high frequency noise should be shielded with metal covers.
Use a good decoupling capacitor
A good high-frequency decoupling capacitor can remove high-frequency components up to 1GHZ. Ceramic chip capacitors or mu