The sensitivity of electronic equipment is getting higher and higher, which requires the anti-interference ability of the equipment to become stronger and stronger, so PCB design has become more difficult. How to improve the anti-interference ability of PCB has become one of the key issues that many engineers pay attention to. This article will introduce some tips for reducing noise and electromagnetic interference in PCB design.
The following are 24 tips for reducing noise and electromagnetic interference in PCB design after years of design:
(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 used in series to reduce the transition rate of the upper and lower edges of the control circuit.
(3) Try to provide some form of damping for relays, etc.
(4) Use the lowest frequency clock that meets the system requirements.
(5) The clock generator is as close as possible to the device using the clock. The quartz crystal oscillator case should be grounded.
(6) Circle the clock area with a ground wire, and keep the clock wire as short as possible.
(7) The I/O drive circuit should be as close to the edge of the printed board as possible, so that it can leave the printed board as soon as possible. Filter the signal entering the printed board, and the signal from the high noise area
It is also necessary to add filtering, and at the same time use the method of string terminal resistance to reduce signal reflection.
(8) The useless end of MCD should be connected to high, or grounded, or defined as an output end. The end of the integrated circuit that should be connected to the power supply ground should be connected, and should not be left floating.
(9) Do not float the input terminal of the gate circuit that is not in use, connect the positive input terminal of the operational amplifier that is not in use to the ground, and connect the negative input terminal to the output terminal.
(10) As far as possible on the printed board, use 45 fold lines instead of 90 fold lines to reduce the external emission and coupling of high-frequency signals.
(11) The printed board is divided according to frequency and current switching characteristics, and the distance between noise components and non-noise components should be further away.
(12) Single-point power supply and single-point grounding for single-panel and double-panel, the power line and ground wire should be as thick as possible. If the economy can afford it, use a multi-layer board to reduce the power supply.
The capacitive inductance of the ground.
(13) The clock, bus, and chip select signals should be kept away from I/O lines and connectors.
(14) The analog voltage input line and the reference voltage terminal should be kept as far away as possible from the digital circuit signal line, especially the clock.
(15) For A/D devices, the digital part and the analog part should be unified rather than crossed.
(16) The clock line perpendicular to the I/O line has less interference than the parallel I/O line, and the clock component pins are far away from the I/O cable.
(17) The component pins should be as short as possible, and the decoupling capacitor pins should be as short as possible.
(18) The key lines should be as thick as possible, and protective ground should be added on both sides. High-speed lines should be short and straight.
(19) The lines sensitive to noise should not be parallel to the high current, high-speed switching lines.
(20) Do not route wires under the quartz crystal and under the devices that are sensitive to noise.
(21) For weak signal circuits, do not form current loops around low-frequency circuits.
(22) No signal should form a loop. If it is unavoidable, make the loop area as small as possible.
(23) One decoupling capacitor per integrated circuit. A small high frequency bypass capacitor should be added beside each electrolytic capacitor.
(24) Use large-capacity tantalum capacitors or polycapacitors instead of electrolytic capacitors as circuit charge and discharge energy storage capacitors. When using tubular capacitors, the case should be grounded.