Views: 0 Author: Site Editor Publish Time: 2019-06-03 Origin: Site
If the frequency of the digital logic circuit reaches or exceeds 45 MHz to 50 MHz, and the circuit operating above this frequency already accounts for a certain amount (for example, 1/3) of the entire electronic system, it is usually called a high frequency circuit. High-frequency circuit design is a very complex design process, and its wiring is critical to the overall design!
[first move] multi-layer board wiring
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. In the PCB Layout stage, a reasonable selection of the printed board size of a certain number of layers can make full use of the intermediate layer to set the shielding, better achieve the near grounding, and effectively reduce the parasitic inductance and shorten the transmission length of the signal, and at the same time All of these methods are advantageous for the reliability of high-frequency circuits by reducing the crosstalk of signals and the like.
According to the data, the four-layer board is 20dB lower than the noise of the double-panel. However, there is also a problem. The higher the PCB half-layer number, the more complicated the manufacturing process and the higher the unit cost. This requires us to select the appropriate number of PCB boards for PCB layout. Proper component layout planning and proper routing rules to complete the design.
[Second measure] The less the lead between the high-speed electronic device pins is bent, the better.
The lead wire of the high-frequency circuit wiring is preferably a full line, which needs to be turned, and can be folded at a 45-degree line or a circular arc. This requirement is only used to improve the fixing strength of the copper foil in the low-frequency circuit, and in the high-frequency circuit, the content is satisfied. One requirement is to reduce the external transmission and mutual coupling of high frequency signals.
[Third measure] The shorter the lead between the pins of the high-frequency circuit device, the better.
The radiant intensity of the signal is proportional to the length of the trace of the signal line. The longer the high-frequency signal lead, the easier it is to couple to the component close to it, so for data such as signal clock, crystal, DDR, High-frequency signal lines such as LVDS lines, USB lines, and HDMI lines are required to be as short as possible.
