printed circuit boards are an important component in the electronic device. Electronic components in position on the board, the stability, reliability and noise immunity and electromagnetic compatibility equal has a significant impact. Rational arrangement of components on the circuit board, either to improve product design quality, they can save time, so as to achieve a multiplier effect. Here is the author of electronic products in the design process of some of the views and ideas.
Using PROTEL FOR PCB circuit design, it will draw a diagram of PROTEL FOR SCH generate the corresponding netlist. When loaded with LOAD NETLIST below the corresponding components, it should be moved to the appropriate location and elements of its properties to let LOCKED tick, so that components can not move. If the system contains a high-power components, high current I / O driver circuit (relays, high current switches, etc.) to try to make it close to the edge of the circuit board. Signals entering the PCB to add filtering to the signal from a high noise filtering also added while terminating resistor with a string of ways to reduce signal reflections.
Idle gates generally do not unconnected inputs to prevent interference signal input. Extra processing on the input state of the circuit without changing the principle of the stability and can be connected to the power supply through pull-up resistor, an inverter can also be used to input grounded, its output connected to a high level of excess input.
PCB to make use of 45 degree line, rather than 90 degree line wiring, preferably with arc-shaped bend in order to reduce the high-frequency signal transmission and external coupling. For Class A / D devices, digital and analog portions rather partial to look around, do not cross. High frequency leads to short and straight. Noise-sensitive lines do not parallel with high current, high speed switching. Pin components as short as possible, but also pin decoupling capacitor as short as possible, especially in high frequency bypass capacitor can not have a lead. Susceptible to interference components can not put too close, to prevent electromagnetic interference between each other.
Anti-jamming capability is weak, turn off the power when changing large devices, such as RAM, ROM memory, should be between the chip's power and ground directly access the decoupling capacitors.
Single-sided and double-sided power supply and a single point of access with a single point grounding, power lines, ground should be thick, but also has more than a ground return circuit, usually three times to make it through the circuit board to allow current to reduce consistent with the direction of the small loop resistance, power lines, ground direction and data signals.
At high frequencies, distributed inductance and distributed capacitance of the lead of the printed circuit board, vias, resistors, capacitors, connectors can not be ignored, the resistance of the high-frequency signal reflection, distributed capacitance will lead to function, when the length is greater than noise frequency corresponding to a wavelength of 1/20, will have an antenna effect, the noise will be emitted out through the leads. So to try to free will.
For those who work in high-current loads such as relays, AC contactors, buttons, coils and other components, they are accompanied by a spark in the running, produce electromagnetic interference, it must adopt parallel RC RC circuit to absorb the current release. Generally R takes 1-2KW, C takes 2.2-4.7Uf., Following the flow of the coil also parallel diode.
