High-speed PCB affects five aspects of signal quality
According to the conclusions of the current work, the common problems of signal quality are mainly manifested in five aspects: overshoot, backlash, glitch, edge, level. Aluminum BASE BOARD.
1) Overshoot
The problem with overshoot is that it is easy to cause damage to the device. If the overshoot is too large, it will easily cause crosstalk to the surrounding signals. The cause of overshoot is mismatch. The method of elimination has a string resistance at the beginning or an end and impedance (or resistance).
2) Glitch
The glitch acts on a high-speed device, which may cause problems such as false triggering, control signal control error, or clock signal phase error. The problems caused by the glitch pulse often occur when the board is unstable or the device is replaced. There are many reasons for glitch, such as logic adventure, crosstalk, ground bounce, etc., and the methods of elimination are not the same.
Single Side Aluminum Base Board.
3) Edge
When the edge speed slowly occurs on the signal line, it will cause data sampling errors. The cause is usually that the capacitive load at the output is too large (the number of loads is too large), and the output is tri-state, and the charge current is small.
4) Backflush
The reason for the backlash is that the signal line is not matched or multi-loaded. The elimination method is to add a matching resistor or adjust the topology of the bus.
Double Side Aluminum Base Board.
5) Level
If the input level does not meet the requirements, it will cause a device output error. The main causes of level anomalies are: output overload, level mismatch, tri-state bus, bus conflict and other reasons.
Extension:
Engineers should have the following three aspects of knowledge when performing signal quality tests:
1)Have a clear understanding of the measurement tools (oscilloscope), understand the performance of the oscilloscope, master the use of the oscilloscope and its probes, and understand the relationship between the test of abnormal signal quality and the menu settings of the oscilloscope.
2) Have a comprehensive and clear understanding of the abnormal signal form, and have an understanding of the abnormal indicators of abnormal signals.
3) Have a certain understanding and understanding of the principle circuit of the tested board. It is required to classify the signal and understand the signal quality requirements and related timing parameters of key components, critical buses, key signals on the board.