PCB and circuit anti - jamming measures
Printed circuit board anti-jamming design and specific circuit has a close relationship, here only on the PCB anti-jamming design of several commonly used measures to do some instructions.
1. Power cord design
According to the size of the printed circuit board current, try to add the power line width, reduce loop resistance. At the same time, make the power line, ground direction and data transmission direction, which will help enhance the anti-noise ability.
2. Principles of ground design
(1) numerically and analogously. If the circuit board has both logic and linear circuits, make them as close as possible. Low-frequency circuit to the ground should try to use a single point of parallel grounding, the actual wiring can be part of the difficulties in parallel and then grounded. High-frequency circuit should adopt a multi-point series grounding, ground should be short and rent, high-frequency components around the grid as large as possible to foil a large area.
(2) grounding wire should be as thick as possible. If the ground wire with a very sewing line, the ground potential changes with the current changes, so that anti-noise performance. So the ground wire should be bolded so that it can pass three times the allowable current on the printed circuit board. If possible, the ground wire should be 2 ~ 3mm or more.
(3) The ground wire forms a closed loop. Only by the digital circuit composed of printed circuit board, the ground circuit cloth into a mass loop can improve the anti-noise ability.
3. Decoupling capacitor configuration
One of the common practices of PCB design is to configure the appropriate decoupling capacitors at each critical part of the PCB. The general configuration principle of the decoupling capacitor is:
(1) power input terminal jumper 10 ~ 100uf electrolytic capacitor. If possible, then more than 100uF better.
(2) In principle, each integrated circuit chip should be arranged a 0.01pF ceramic capacitors, in case of PCB gap is not enough, each 4 to 8 chips arranged a 1 ~ 10pF tantalum capacitors.
(3) for anti-noise ability, power off when the device changes, such as RAM, ROM memory devices, the chip should be directly connected between the power cord and ground decoupling capacitor.
(4) Capacitive lead can not be too long, especially high frequency bypass capacitor can not have lead.
(5) When there are contactors, relays, buttons and other components in the printed circuit board. Operation of these will produce a larger spark discharge, RC circuit must be used to absorb the discharge current. General R take 1 ~ 2K, C take 2.2 ~ 47UF.
(6) CMOS input impedance is high, and susceptible to induction, so when used in the end do not have to be grounded or positive power supply.