PCB News - Placement of terminal matching resistors in high-speed PCB design

With the rapid development of semiconductor technology, the signal rise time is getting shorter and shorter, leading to increasingly prominent signal integrity problems; in addition, the trend of device miniaturization is also becoming increasingly obvious, and the area of the circuit board is getting smaller and smaller, so the layout of the PCB board The requirements are also becoming stricter. 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 printed board area.

Advantages and disadvantages of parallel terminal matching and series terminal matching

In high-speed digital designs, resistors are often used to match the impedance of the transmission line to eliminate reflections on the transmission line. There are two most typical and simple matching methods: simple parallel terminal matching and series terminal matching. The simple parallel terminal matching resistor is connected in parallel with the receiving end with extremely high input impedance, and is grounded or powered to eliminate the reflection of the receiving end. The advantage and disadvantage is that the resistance of the matching resistor can be selected more accurately but it will consume DC power consumption. The series source end matching resistor is connected in series with a driver with a 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 varies with the device. The logic state changes, which makes it difficult to determine the resistance of the matching resistor. Therefore, in the digital design that requires low power consumption, the series terminal matching method is more commonly used; the parallel terminal matching method is more used in analog circuit design to meet the high precision requirements at the expense of power consumption. This article will summarize another advantage of the series terminal matching method, that is, its matching resistance in the PCB board is not as strict as the simple parallel terminal matching method.

The above is an introduction to the placement of terminal matching resistors in high-speed PCB design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.