High-frequency circuit board design is a very complicated design process, and its wiring is essential to the entire design! With the continuous development and progress of electronic technology, large-scale high-precision PCB circuit boards have been widely used, components in printed circuits The mounting density on the board is getting higher and higher. Simple single-sided and double-sided wiring can no longer meet the high-performance circuit requirements, so multilayer PCB circuit boards are needed for wiring. Wiring rules for multilayer PCB circuit boards:
High-frequency circuits are often highly integrated and have high wiring density. The use of multi-layer boards is not only necessary for wiring, but also an effective means of reducing interference. In the PCB Layout stage, the size of a certain number of printed boards is reasonably selected, the middle layer can be used to set the shield, the grounding can be better achieved nearby, and the parasitic inductance and the transmission length of the signal can be effectively reduced. Reducing the cross-interference of the signal by amplitude, etc. All these methods are beneficial to the reliability of high-frequency circuits.
1. When connecting more than 3 points, try to make the line pass through each point in order to facilitate testing, and the length of the line should be as short as possible.
2. The lines between different layers should not be parallel as much as possible to avoid the formation of actual capacitance.
3. Try not to put wires between pins, especially between and around integrated circuit pins.
4. The wiring should be as straight as possible, or a 45-degree broken line to avoid electromagnetic radiation.
5. The lines should be as neat as possible, and the polyline should be connected together as much as possible to increase the grounding area.
6. The discharge of components should be more uniform to facilitate installation, plug-in and welding operations. The text is arranged in the current character layer, the position is reasonable, pay attention to the orientation, avoid being blocked, and easy to produce.
7. Consider the structure of component discharge. The positive and negative poles of the chip components should be marked at the end of the package to avoid space conflicts.
8. The functional block components should be put together as far as possible, and the components near the LCD such as zebra strips should not be too close.
9. After the wiring is completed, carefully check whether each link is really connected (the lighting method can be used).
The fewer lead bends between the pins of high-speed electronic devices, the better
The high-frequency circuit wiring lead is best to use a full straight line, which needs to be turned, and can be turned with a 45-degree fold line or an arc. This requirement is only used to improve the fixation strength of the copper foil in low-frequency circuits, while in high-frequency circuits, it meets this requirement. One requirement can reduce the external emission and coupling of high-frequency signals.
Under the conditions allowed by the wiring space, inserting a ground wire or ground plane between the two wires with more serious crosstalk can play an isolation role and reduce crosstalk.
When there is a time-varying electromagnetic field in the space around the signal line, if parallel distribution cannot be avoided, a large area of ”ground” can be arranged on the opposite side of the parallel signal line to greatly reduce interference.
Under the premise that the wiring space permits, increase the spacing between adjacent signal lines and reduce the parallel length of the signal lines. The clock lines should be perpendicular to the key signal lines as much as possible rather than parallel.
HDMI wiring rules. Requires HDMI signal differential routing, line width 10mil, line spacing 6mil, the distance between each two sets of HDMI differential signal pairs exceeds 20mil.
LVDS wiring rules. Requires differential traces for LVDS signals, with a line width of 7 mils and a line spacing of 6 mils. The purpose is to control the impedance of the HDMI differential signal pair to 100+-15% ohms
DDR wiring rules. DDR1 wiring requires that the signal should not pass through the hole as much as possible, the signal line is the same width, and the line is equidistant from the line. The trace must meet the 2W principle to reduce crosstalk between signals. For high-speed devices of DDR2 and above, high-frequency data is also required. The wires are of equal length to ensure the impedance matching of the signal.