Several important embodiment of signal reflection (overshoot, undershoot, ringing) and circuit design

This article highlights:

1, introduce the specific performance of the signal breakdown reflection;

2, combined with specific circuit analysis.

When the signal travels forward along the transmission line, a transient impedance is sensed every moment, which may be the transmission line itself, or the other component in the middle or end. For a signal, it does not distinguish between what it is, but the impedance that the signal senses. If the signal feels the impedance is constant, then he will normally spread forward, as long as the sensed impedance changes, the signal will be reflected. These factors may include excessively long lines, end-matched transmission lines, excessive capacitance or inductance, and impedance mismatch.

The reflection will cause the signal overshoot overshoot, the undershoot undershoot, the ringing ringing, the edge delay (the callback phenomenon) is also the ladder voltage wave. The overshoot is the under-damping state of the ringing, and the edge retardation is the over-damping state of the ringing. When the first crest of the signal exceeds the originally set maximum value. Overshoot refers to the first peak or valley value of the signal jump, which is the additional voltage effect above or below the reference ground level;

Edge Delay We also become a step, the hook phenomenon, the danger is mainly caused by a false trigger.

Undershoot refers to the next valley or peak of a signal's transition. Overshoot and undershoot are unfavorable factors, too large overshoot voltage often long-term impact will cause damage to the device, as shown in. A severe undershoot will exceed the threshold of the receiving device and cause a logic error in the circuit.

If the signal bounces back and forth between the driver and receiver, a ringing phenomenon is generated, which increases the time required for the signal to stabilize, and thus also affects the timing of the system's stability.

Details such as,

Circuit Design Tips:

In general circuit design, if the clock signal link is longer, the clock output signal will be connected to a small resistor, such as 22 ohms or 33 ohms.

As for why, a lot of mature design is doing so, is a kind of experience design method. In fact, the effect of this small resistor is to solve the problem of signal reflection. And as the resistance increases, the ringing will disappear, but you will notice that the signal rising edge is no longer so steep, the series resistance is to reduce the reflected wave, to avoid the reflection wave superposition caused overshoot. This solution is called impedance matching, must pay attention to impedance matching, impedance in the signal integrity problem occupies an extremely important position.

Several important embodiment of signal reflection (overshoot, undershoot, ringing) and circuit design