Placement of Terminal Matching Resistance in High Speed PCB Design

Placement of Terminal Matching Resistance in High Speed PCB Design

The design of printed circuit board is based on the circuit schematic diagram to realize the functions required by the circuit designer. The design of printed circuit board mainly refers to layout design, which needs to consider the layout of external connections. The optimal layout of internal electronic components, the optimal layout of metal wiring and through-hole, electromagnetic protection, heat dissipation and other factors. Excellent layout design can save production costs and achieve good circuit performance and heat dissipation. Simple layout design can be realized by hand, while complex layout design needs to be realized by computer aided design (CAD)

This paper briefly summarizes the advantages and disadvantages of series terminal matching and parallel terminal matching in high-speed digital design, and makes corresponding simulation and in-depth analysis of the matching effect when the terminal matching resistors of these two matching methods are in different positions. It is concluded that the position requirements of series terminal matching resistors are less strict than that of terminal matching resistors, and some suggestions on the placement of terminal matching resistors are given. It provides theoretical and practical guidance on how to place terminal matching resistors in PCB design.

With the rapid development of semiconductor technology, the signal rise time is getting shorter and shorter, which leads to the increasingly prominent problem of signal integrity; In addition, the trend of device miniaturization is becoming increasingly obvious, and the area of the circuit board is also becoming smaller and smaller, so the layout requirements for the PCB are increasingly strict. This requires high-speed PCB design engineers to strictly consider the placement of various devices, including filter capacitors, matching resistors, etc., to improve the signal integrity of the system while saving PCB area. Simple parallel terminal matching and series terminal matching are simulated and analyzed to study the influence of matching resistance at different positions on signal quality.

2 Advantages and disadvantages of parallel terminal matching and series terminal matching

In high-speed digital design, resistors are often used to match the impedance of transmission lines to eliminate reflection on transmission lines. There are two typical and simple matching methods: simple parallel terminal matching and series terminal matching. The matching resistance of the simple parallel terminal is connected in parallel with the receiving terminal with extremely high input impedance, and is grounded or powered to eliminate the reflection of the receiving terminal. The advantage and disadvantage are that the resistance value of the matching resistance can be accurately selected, but it will consume DC power consumption. The matching resistance at the source end in series is connected in series with the driver with small output impedance to absorb the signal reflected from the receiving end. The advantage and disadvantage of this method is that it does not consume power. However, because many drivers are nonlinear, such as TTL devices, their output impedance changes with the change of the logic state of the device, which makes it difficult to determine the resistance of the matching resistance. Therefore, in the digital design requiring low power consumption, the serial terminal matching mode is more commonly used; Parallel terminal matching mode is more used in analog circuit design to meet its high-precision requirements at the expense of power consumption. This paper will summarize another advantage of the series terminal matching mode, that is, the matching resistance in the PCB has less strict requirements on the position than the simple parallel terminal matching mode. PCB processing and PCBA processing manufacturers will explain the advantages and disadvantages of serial terminal matching and parallel terminal matching in high-speed digital design.