PCB Technical - Some experience of reducing noise and EMI by PCB

PCB, also known as printed circuit board, can realize the circuit connection and function realization between electronic components, and is also an important part of power circuit design. Today, ipcb introduces some experience of PCB to reduce noise and EMI.

(1) If you can use low-speed chips, you don't need high-speed chips. High-speed chips are used in key places.

(2) A resistor can be connected in series to reduce the jump rate of the upper and lower edge of the control circuit.

(3) Try to provide some form of damping for relays, etc.

(4) Use a frequency clock that meets the system requirements.

(5) The clock generator shall be as close as possible to the device using the clock. The quartz crystal oscillator shell should be grounded.

(6) Circle the clock area with ground wire, and the clock line shall be as short as possible.

(7) The I / O driver circuit should be close to the printed board as far as possible, so that it can leave the printed board as soon as possible. The signal entering the printed circuit board should be filtered, and the signal from high noise area should also be filtered. At the same time, the method of series terminal resistance is used to reduce the signal reflection.

(8) The useless terminal of MCD should be connected high, or grounded, or defined as the output terminal. The grounding end of the integrated circuit should be connected, not suspended.

(9) The input end of the unused gate circuit should not be suspended. The positive input terminal of the unused operational amplifier should be grounded, and the negative input terminal should be connected to the output terminal.

(10) In order to reduce the transmission and coupling of high-frequency signals, the PCB should use 45 fold line instead of 90 fold line.

(11) The printed circuit board is divided according to the switching characteristics of frequency and current, and the noise components and non-noise components should be farther away.

(12) Single point grounding power supply and single point grounding shall be used for single panel and double-sided board. The power line and ground wire shall be as thick as possible. If the economy is affordable, multilayer board shall be used to reduce the capacitance inductance of power supply and ground.

(13) Clock, bus and chip selection signal should be away from I / O line and connector.

(14) Analog voltage input line and reference voltage terminal should be far away from digital circuit signal line, especially clock.

(15) For a / D devices, the digital part and the analog part would rather be unified than crossed.

(16) The interference of clock line perpendicular to I / O line is smaller than that of parallel I / O line, and clock component pin is far away from I / O cable.

(17) The component pin should be as short as possible, and the decoupling capacitor pin should be as short as possible.

(18) The key lines should be as thick as possible, and protective areas should be added on both sides. High speed lines should be short and straight.

(19) Noise sensitive lines should not be parallel to high current, high-speed switching lines.

(20) Do not wire under quartz crystal and noise sensitive devices.

(21) do not form current loop around weak signal circuit and low frequency circuit.

(22) do not form a loop for any signal. If unavoidable, keep the loop area as small as possible.

(23) one decoupling capacitor for each IC. A small high frequency bypass capacitor should be added to each electrolytic capacitor.

(24) use large capacity tantalum capacitor or juku capacitor instead of electrolytic capacitor as circuit charge discharge energy storage capacitor. When using tubular capacitors, the enclosure should be grounded.