High-frequency circuit board and high-speed circuits have gradually made circuit boards more and more sophisticated. High-frequency and high-speed circuit boards have become one of the important development trends of modern electronic product substrates. High-frequency and high-speed digitization of signal transmission forces PCB circuit boards to move toward microvias and buried/blind vias, wire refinement, and uniformly thin dielectric layers. High-frequency, high-speed, high-density multi-layer high-speed PCB design technology has become an important research field. Now IPCB will share with you the precautions for high-speed PCB design and high-frequency PCB design and wiring.
High frequency circuit board
High frequency circuit board PCB design
1. Reasonably choose the number of layers
In high-frequency circuit board PCB design, when wiring the high-frequency circuit board, the middle inner plane is used as the power and ground layer to act as a shield, effectively reducing parasitic inductance, shortening the length of signal lines, and reducing interference between signals. cross interference. Generally speaking, the noise of a four-layer board is 20dB lower than that of a two-layer board.
2. High frequency choke
When wiring the high-frequency circuit board in the PCB design of the high-frequency circuit board, when the digital ground, analog ground, etc. are connected to the public ground wire, a high-frequency choke device must be connected, usually a high-frequency ferrite bead with a wire through the center hole. .
3. Signal line
When wiring high-frequency circuit boards in high-frequency circuit board PCB design, signal routing cannot be looped and needs to be routed in a daisy chain manner.
4. Interlayer wiring direction
In high-frequency circuit board PCB design, when wiring high-frequency circuit boards, the wiring direction between layers should be vertical, that is, the top layer is horizontal and the bottom layer is vertical, which can reduce interference between signals.
5. Number of vias
In high-frequency circuit board PCB design, when wiring high-frequency circuit boards, the fewer the number of vias, the better.
6. Copper coating
When wiring high-frequency circuit boards in PCB design, adding grounded copper can reduce interference between signals.
7. Decoupling capacitor
When wiring high-frequency circuit boards in high-frequency circuit board PCB design, decoupling capacitors are connected across the power supply terminals of the integrated circuits.
8. Trace length
When wiring high-frequency circuit boards in high-frequency circuit board PCB design, the shorter the trace length, the better, and the shorter the parallel distance between two lines, the better.
9. Package land
In high-frequency circuit board PCB design, when wiring the high-frequency circuit board, wrapping important signal lines can significantly improve the anti-interference ability of the signal. Of course, it can also wrap the source of interference so that it does not interfere with other signals.
10. Wiring method
In high-frequency circuit board PCB design,when wiring the high-frequency circuit board, the wiring must be rotated at an angle of 45°, which can reduce the transmission and mutual coupling of high-frequency signals.
High-speed circuit board design methods
1. The system, board level, package, and chip interact with each other and cannot be considered in isolation. Issues such as signal integrity, power integrity, EMC, etc. should be considered from the beginning of system design, and the chip design includes package design, device selection, board Extreme design and other aspects are ensured, and these aspects should be considered in the design collaboratively.
2. Digital signals need to study their characteristics from an analogy perspective. With the increase in system speed, density, and complexity, more and more digital systems exhibit certain analog characteristics, which requires studying their characteristics from an analogy perspective when designing digital circuits. , such as the threshold voltage range and overshoot tolerance of digital signals are all analog quantities. Only by considering these effects can we ensure that the chips in the system can cooperate correctly and work stably.
3. High-speed circuit board design experience. Although there are many simulation tools that can help us design high-speed circuits, people still come first. High-speed circuit design relies on the experience of hardware engineers, so attention should be paid to the accumulation of development experience.
4. Extract design rules from design practice, form a series of design rules to guide hardware development and design, and achieve technological accumulation.
5. High-speed circuit board simulation, simulation technology has become mature and is a very effective design method. If the simulation model and method used are correct, the simulation results and objective results should be consistent. In particular, simulation during the planning stage can avoid subsequent remediation and shorten the product development cycle.
6. High-speed circuit board testing verifies the correctness of the design through testing, such as reliability testing, instrument testing, etc. Of course, the interaction between the test equipment and the object being tested will cause some test results to deviate from the true value.
7.High-speed circuit board process control
Try to solve problems in the design stage and rely on design to solve problems instead of discovering problems and trying to solve them in the testing and verification stage. In fact, after the product is made, there are very few changes that can be made, and the result is often that the progress cannot be guaranteed. Cost is not guaranteed.
There should always be the idea that if you try to design the main performance and reliability quotas once, you will be successful. Instead of pinning your hopes on the second and third editions.
Complex high-speed system design is a systematic project, and each program is coherent, from plan formulation, to schematic design, simulation design, PCB physical implementation, to prototype debugging, and the order cannot be reversed.
As mentioned earlier, high-speed issues must be considered at the beginning of the design and efforts must be made to solve them. If problems are discovered after the product is produced, the entire hardware design process can only be repeated to correct the errors, which cannot prevent other new problems.
Incorporate simulation analysis into each stage of the hardware design process to minimize the occurrence of problems in the later stages.
High-speed circuit board design process is simply divided into four steps
1.Signal integrity and timing simulation analysis and obtain the solution space. The solution space is to find the best space in the design stage and does not pursue the unique solution. For example, PCB trace length, spacing, impedance, stacking thickness design, etc. should all be range values to ensure high performance and high reliability of the system, rather than a single fixed value, which limits the flexibility of the design and is actually impossible to process. realized.
2.Stacking and power/ground plane design.
3.Power supply integrity design, such as the placement and location of capacitors.
4.Post-simulation of signal/power integrity.
The above are the precautions for high speed PCB design and high-frequency PCB design and wiring shared by iPCB.