PCB Blog - Ground bounce of high-speed circuit PCB board

Ground bounce of high-speed circuit PCB board. As shown in the figure is a complete signal loop, U1 is the driver; U2 is the receiver; L1, L3 are the package inductance of the component UI signal output pin and ground pin respectively; L2, L4 are the component U2 signal output pin and Package inductance of the ground pin. Consider a simple case where the reference plane of the signal path is the "ground" of the device UI, U2, and the component's signal and ground pins are not in close proximity.

According to the basic laws of electromagnetism, when there is current passing through the loop, magnetic coils are generated around both the signal path and the return path, and the magnetic field lines around one of the paths' total turns are the magnetic coils (self-magnetic coils) generated by the current in that path. It is composed of two parts of the magnetic coil (mutual magnetic coil) generated by other current paths around it. That is to say, the conductor through which the signal current flows has an inductance, and its total inductance consists of two parts: self-inductance and mutual inductance. The current directions of the two paths are opposite, and the directions of the magnetic coils are also opposite, so the total inductance of a path is the difference between the self-inductance and the mutual inductance. If the self-inductance of the signal path is LA; the self-inductance of the return path is LB; the mutual inductance between the two is LAB; then the total inductances of the signal path and return path are:

If the current in the loop changes, an induced voltage will develop across all inductors. The voltage generated on the return path is the ground bounce (Ground Bounce). The ground bounce voltage depends on the speed of the current change. The magnitude is:

Ground bounce is the voltage between two points on the return path, which is created by rapidly changing currents in the loop. The ground bounce has little effect on the driving end, and mainly affects the reception, which is equivalent to the noise superimposed on the received signal. If there are multiple output gates switching states at the same time, the ground bounce noise will increase several times, that is, synchronous switching noise. There are only two ways to reduce the ground bounce voltage:
1) Minimize the variation of loop current. This means reducing edge change rates and limiting the number of signal paths that share the return path;
2) Second, minimize the return path inductance as much as possible. Reducing the return path inductance includes two aspects: reducing the self-inductance of the return path and increasing the mutual inductance between the signal path and the return path. Decreasing the self-inductance means making the return path as loose as possible; increasing the mutual inductance means making the return and signal paths as close as possible.

Here are some specific measures:
1) Use a multilayer board to lay out the power supply and ground reference plane, and directly solder the power supply pins and ground pins of the components on the plane to ensure the inductance and impedance of the power supply or ground pins;
2) Try to use components with low switching speed;
3) For components, a ground pin can be added during packaging, an additional power supply pin can be allocated for the power stage, and a ground reference pin can be allocated for the input circuit;
4) Use the check-point input method;
5) Avoid using sockets and winding boards;
6) Place the decoupling capacitor as close as possible to the ground pin of the component.
Ground bounce is a source of noise generated by logic components. Due to the faster and faster edge rates of signals and voltage switching, ground bounce can sometimes become a serious problem and should be designed with more attention on PCB board.