Experience in PCB design

- Oct 17, 2018-

Printed circuit board size should be moderate, too large when printed line long, impedance increased, not only anti-noise capacity reduction, high cost;Too small, heat is not good, at the same time easy to be disturbed by adjacent lines.As with other logic circuits, the device should be placed as close as possible to obtain better anti-noise effect.Clock generator, crystal oscillator and CPU clock input are easy to generate noise, closer to each other.Devices that are prone to noise, small current circuits, large current circuits and so on should be as far away from the logic circuit as possible, if possible, should be another circuit board, this is very important.

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Decoupling capacitance configuration

Decoupling capacitance configuration

In dc power loop, the change of load will cause power noise.In digital circuits, for example, when a circuit switches from one state to another, a large spike of current is generated on the power line, creating a transient noise voltage.It is a common practice for the reliability design of printed circuit boards to configure decoupling capacitors to suppress the noise caused by load changes.

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The configuration principle is as follows

The configuration principle is as follows

The power input terminal is connected with an electrolytic capacitor of 10 ~ 100uF. If the position of printed circuit board is allowed, the anti-interference effect of electrolytic capacitor above 100uF will be good.

Each IC chip is equipped with a 0.01uF ceramic capacitor.If printed circuit board and a small space, can every 4 ~ 10 chip configuration a 1 ~ 10 uf tantalum electrolytic capacitor, this particularly small high frequency impedance of the device in 500 KHZ ~ 20 MHZ range impedance is less than 1 Ω, and leakage current is very small (below 0.5 uA).

For weak noise, shut off the current change device and ROM, RAM, storage devices, such as should be the power cord of the chip (Vcc) and ground (GND) direct access to the decoupling capacitor.

Decoupling capacitor lead cannot too long, especially high frequency bypass capacitors can't lead.