Introduction To High Frequency Circuit PCB Design Skills Part 2

In the previous article, we introduced five high-frequency circuit PCB design techniques, but in fact, there are not only these five in the actual process. Then please ask the professional technicians of Taike Electronics to continue to introduce to you, what skills are there for PCB high-frequency circuits!

Add high-frequency decoupling capacitor to the power supply pin of the integrated circuit block

A high-frequency decoupling capacitor is added to the power supply pin of each integrated circuit block nearby. Increasing the high-frequency decoupling capacitor of the power supply pin can effectively suppress the interference of high-frequency harmonics on the power supply pin.

Add a high-frequency decoupling capacitor near the power supply pin of each integrated circuit block. Increasing the high-frequency decoupling capacitor of the power supply pin can effectively suppress the interference of high-frequency harmonics on the power supply pin.

The ground wire of high-frequency digital signal is isolated from the ground wire of analog signal

When the analog ground wire and digital ground wire are connected to the common ground wire, high-frequency choke magnetic beads should be used for connection or direct isolation, and a suitable location should be selected for single-point interconnection. The ground potential of the high-frequency digital signal ground wire is usually inconsistent. There is usually a certain voltage difference between the two. In addition, the ground wire of a high-frequency digital signal usually contains very rich harmonic components in the high-frequency signal. When the digital signal ground wire and the analog signal ground wire are directly connected, the harmonics of the high-frequency signal will interfere with the analog signal through the ground wire coupling. Therefore, under normal circumstances, the ground wires of high-frequency digital signals and analog signals should be isolated. The single-point interconnection method or the high-frequency choke coil interconnection method at an appropriate location can be used.

Avoid loops formed by wiring

All kinds of high-frequency signal traces should not form a loop as much as possible. If it is unavoidable, the loop area should be as small as possible.

Must ensure good signal impedance matching

In the signal transmission process, when the impedance does not match, the signal will be reflected in the transmission channel. The reflection will cause the synthesized signal to form an overshoot, causing the signal to fluctuate around the logic threshold.

The fundamental way to eliminate reflections is to match the impedance of the transmitted signal well. Since the greater the difference between the load impedance and the characteristic impedance of the transmission line, the greater the reflection, so the characteristic impedance of the signal transmission line should be as equal to the load impedance as possible. At the same time, it should be noted that the transmission line on the PCB should not have sudden changes or corners, and try to keep the impedance of each point of the transmission line continuous, otherwise there will be reflections between the various segments of the transmission line. This requires that the following wiring rules must be observed during high-speed PCB wiring:

USB wiring rules. The USB signal differential routing is required, the line width is 10mil, the line spacing is 6mil, and the ground line and signal line spacing is 6mil.

HDMI wiring rules. The HDMI signal differential routing is required, the line width is 10mil, the line spacing is 6mil, and the spacing between each two sets of HDMI differential signal pairs exceeds 20mil.

LVDS wiring rules. Requires LVDS signal differential routing, line width 7mil, line spacing 6mil, the purpose is to control the differential signal impedance of HDMI to 100+-15% ohm

DDR wiring rules. DDR1 traces require signals not to go through holes as much as possible. The signal lines have the same width and the same distance between the lines. The traces must meet the 2W principle to reduce crosstalk between signals. For DDR2 and above high-speed devices, high-frequency data routing is also required. The lines are equal in length to ensure the impedance matching of the signal.

Guarantee the integrity of the transmission

Maintain the integrity of signal transmission and prevent the "ground bounce phenomenon" caused by ground splitting.

In addition to the previous article, we have introduced a total of ten high-frequency circuit PCB design techniques! Hope to provide you with some reference!