2019年11月11日星期一

Tips for designing high frequency board layout

  • Tips for designing high frequency board layout


(1) High-frequency circuits tend to have high integration and high wiring density. The use of multi-layer boards is both necessary for wiring and an effective means to reduce interference.
(2) The less the lead bend between the pins of the high-speed circuit device, the better. It is better to use full straight line for high frequency circuit wiring. If turning is needed, 45 degree break line or arc turning can be used. Once meeting this requirement, the external transmission of high frequency signals and the coupling between them can be reduced.
(3) The shorter the lead between the pins of high frequency circuit devices, the better.
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(4) The fewer lead layers alternating between pins of high frequency circuit devices, the better. It means that the fewer Via holes used in the process of component connection, the better. Reducing the number of Via holes can significantly improve the speed.
(5) High-frequency circuit wiring should pay attention to the “cross interference” introduced by the parallel lines of the signal lines.Parallel lines in the same layer are almost unavoidable, but in the two adjacent layers, the directions of the lines must be perpendicular to each other.
(6) As to signal lines or partial units of particular importance,implementing the measures of ground line encirclement, i. e. drawing the outline of the selected object.
(7) All kinds of signal routes can not form a loop, and ground wires can not form a current loop.
(8) A high frequency decoupling capacitor should be installed near each IC block.
(9) High-frequency chock be used when connecting analog ground lines and digital ground lines to public ground lines.Most of the high frequency ferrite beads with central holes through conducting wires are used in the actual assembly of high frequency choke links,and it is generally not expressed on the circuit schematic, and the resulting netlist is not Including such components, the wiring will ignore its existence. In view of this reality, it can be regarded as an inductance in the schematic diagram, and a component package can be defined separately in the PCB component library. Before wiring, it can be manually moved to a suitable location near the common ground wire confluent.
(10) The analog circuit and the digital circuit should be arranged separately. After independent wiring, power supply and ground wire should be connected at a single point to avoid mutual interference.
(11) Before the DSP, off-chip program memory and data memory are connected to the power supply, the filter capacitor should be added and placed as close as possible to the chip power supply pin to filter out the power supply noise. In addition, shielding is recommended around the DSP and off-chip program memory and data memory to reduce external interference.
(12) When making the printed circuit board (PCB) of the DSP hardware system, special attention should be paid to the wiring of important signal lines such as address lines and data lines to be correct and reasonable. When wiring, try to use short and thick high-frequency line,and keep away from the signal lines that are susceptible to interference, such as analog signal lines. When the circuit around the DSP is more complicated, it is recommended to make the DSP and its clock circuit, reset circuit, off-chip program memory, and data memory into a minimum system to reduce interference.

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