In high-speed PCB design, “signal” is an essential topic that engineers cannot overlook. Whether during the design phase or testing phase, signal quality demands careful consideration. In this article, we will primarily explore the five major issues that impact signal quality.
Based on current findings, the common signal quality problems are primarily evident in five areas: overshoot, backwash, burr, edge, and level.
1) **The Overshoot**
Include a figure.
Overshoot can easily lead to device damage and may also cause crosstalk affecting nearby signals. The primary cause of overshoot is impedance mismatch, which can be mitigated by implementing series resistance or parallel resistance at the terminals.
2) **The Burr**
Include a burr figure.
When burrs impact high-speed devices, they can result in misfiring, control signal errors, or clock signal phase discrepancies. Issues related to burrs typically arise during board instability or device replacement. Causes of burrs include logic risks, crosstalk, and ground bounce, with various elimination techniques required for each.
3) **The Edge**
Include an edge figure.
Slow edge rates on signal lines can lead to data sampling errors. This issue is often due to excessive capacitive loading at the output terminal and insufficient charging or discharging currents during three-state operations.
4) **Rushed Back**
Include a backflush figure.
Backflush occurs due to mismatched signal lines or excessive loads, which can be addressed by adding matching resistors or adjusting the bus topology.
5) **Level**
Include a level figure.
If the input level amplitude is inadequate, it can lead to output errors in devices. Common causes of level abnormalities include output overloads, level mismatches, three-state bus issues, and bus conflicts.
**Extension:**
Engineers should possess the following knowledge when performing signal quality tests:
1) A solid understanding of the measuring tool (oscilloscope), including its performance, proper usage, and the relationship between abnormal signal quality tests and oscilloscope settings.
2) A comprehensive grasp of abnormal signal forms and their indicators.
3) Knowledge of the principle circuit of the tested board, enabling signal classification, identification of key components and buses, and understanding the signal quality requirements and timing parameters of critical signals.
Based on current findings, the common signal quality problems are primarily evident in five areas: overshoot, backwash, burr, edge, and level.
1) **The Overshoot**
Include a figure.
Overshoot can easily lead to device damage and may also cause crosstalk affecting nearby signals. The primary cause of overshoot is impedance mismatch, which can be mitigated by implementing series resistance or parallel resistance at the terminals.
2) **The Burr**
Include a burr figure.
When burrs impact high-speed devices, they can result in misfiring, control signal errors, or clock signal phase discrepancies. Issues related to burrs typically arise during board instability or device replacement. Causes of burrs include logic risks, crosstalk, and ground bounce, with various elimination techniques required for each.
3) **The Edge**
Include an edge figure.
Slow edge rates on signal lines can lead to data sampling errors. This issue is often due to excessive capacitive loading at the output terminal and insufficient charging or discharging currents during three-state operations.
4) **Rushed Back**
Include a backflush figure.
Backflush occurs due to mismatched signal lines or excessive loads, which can be addressed by adding matching resistors or adjusting the bus topology.
5) **Level**
Include a level figure.
If the input level amplitude is inadequate, it can lead to output errors in devices. Common causes of level abnormalities include output overloads, level mismatches, three-state bus issues, and bus conflicts.
**Extension:**
Engineers should possess the following knowledge when performing signal quality tests:
1) A solid understanding of the measuring tool (oscilloscope), including its performance, proper usage, and the relationship between abnormal signal quality tests and oscilloscope settings.
2) A comprehensive grasp of abnormal signal forms and their indicators.
3) Knowledge of the principle circuit of the tested board, enabling signal classification, identification of key components and buses, and understanding the signal quality requirements and timing parameters of critical signals.
