High speed PCB layout

The layout of high-speed PCB basically determines the general direction and structure of wiring, the division of power and ground planes, and the control of noise and EMI. The general layout principles are——

Understand the system schematic diagram, divide digital, analog, and hybrid digital/analog components in each circuit, and pay attention to the positioning of the power supply and signal pins of each chip;

According to the proportion of each part in the circuit, preliminarily divide the wiring areas of digital and analog circuits on the PCB, so that the digital components, analog components, and their corresponding wiring are as far away as possible and limited within their respective wiring areas. After division, the general order is hybrid devices ->analog devices ->digital devices ->bypass capacitors

The digital analog hybrid components are placed at the junction of the digital signal area and the analog signal area, and the placement direction should pay attention to the orientation of the digital signal and analog signal pins of the chip towards their respective wiring areas. Pure digital or analog components should be placed within their respective specified ranges, and crystal oscillator circuits should be placed as close as possible to their driver components;

Devices sensitive to noise should be kept away from high-frequency signal wiring, such as feedback voltage Fb. Sometimes, signal wiring that requires restrictions needs to be adjusted based on length and structure. Bypass capacitors should be placed as close as possible to the power pins, especially high-frequency capacitors. Place large capacity capacitors near the power interface to maintain power stability and reduce low-frequency noise interference.

High speed PCB wiring

High speed PCB wiring involves a lot of details and is more flexible. With a reasonable layout as the premise and basic wiring principles, we can avoid unexpected signal integrity or timing issues——

Reasonably select the number of layers. High frequency circuits have high integration and high wiring density. Reasonable use of multi-layer boards can use intermediate layers to set shielding, better achieve grounding, effectively reduce parasitic inductance, shorten signal transmission length, and reduce cross interference between signals.

Reduce the bending of leads between pins of high-speed circuit components. It is best to use a full straight line for high-frequency lines. When bending is required, a 45 ° line or arc line can be used to avoid signal refraction;

Shorten the length of high-frequency leads;

Reduce interlayer overlap of high-frequency leads. Reduce the number of vias used during the wiring process. One vias can bring about 0.5pf of distributed capacitance, and reducing the number of vias can reduce the impact on signal speed;

Pay attention to the cross interference that may be introduced when wiring signal lines in close proximity. If parallel distribution cannot be avoided, a large area of ground wire can be arranged on the opposite side of the parallel lines and between the lines. In practical operation, parallel wiring within layers is almost inevitable, but the wiring directions of adjacent two layers must be perpendicular to each other, that is, the wiring directions of adjacent two layers must be parallel, horizontal, and vertical respectively;

Apply grounding measures to particularly sensitive signal lines or local units. If the clock unit is grounded;

Various signal wiring cannot form a loop, nor can it form a current loop;