Singnal Integrity refers to the ability of a signal to produce the correct corresponding power in a circuit. Signals with good signal integrity (Singnal Integrity) are those that have to be reached when needed. The main signal integrity issues include reflection, oscillation, ground bounce, crosstalk, and so on. Common signal integrity problems and solutions:
2. What is crosstalk?
Crosstalk refers to the interaction between two different electrical properties. The crosstalk is called Aggressor, and the other is called Victim. Usually, a network is both an Aggressor (intruder) and a Victim (victim). Ringing and ground bombs are all phenomena of single signal lines in signal integrity problems (with ground plane loops). Crosstalk is caused by two signal lines and ground planes on the same PCB board. It is also called a three-wire system. . Crosstalk is the coupling between two signal lines. The mutual inductance and mutual capacitance between the signal lines cause noise on the line. Capacitive coupling induces a coupling current, while inductive coupling induces a coupling voltage. PCB board layer parameters, signal line spacing, electrical characteristics of the driver and receiver terminals, and line termination methods all have a certain impact on crosstalk.
3. What is electromagnetic compatibility (EMI)?Electromagnetic interference (Ectromagnetioc Interference), or electromagnetic compatibility (EMI), is the result of having antenna characteristics obtained from a transmission line such as a cable, wire or packaged pin. Printed circuit boards, integrated circuits, and many cables emit and affect electromagnetic compatibility (EMI) issues. The FCC defines the level of maximum emissions for a given frequency (eg, applied to the field of flight controllers).
4. What is the difference between the time domain and the frequency domain?
The time domain is a waveform oscilloscope observation. It is usually used to find pin-to-pin delays, skews, overshoots, undershoots, and settings. Time (setting times). The frequency domain is a spectrum analysis of a waveform. It is commonly used for waveform and spectrum analysis observations. It is typically used to compare waveforms with FCC and other EMI control limits. (There is a metaphor, it's like a radio - you hear it in the time domain, but you have to find the station you like in the frequency domain.)
5. What is a transmission line?
A transmission line is a network (wire) and its current is returned to ground and power. The wires on the board have electrical characteristics such as resistance, capacitance, and inductance. In high frequency circuit design, the capacitance and inductance on the board traces make the conductor equivalent to a transmission line. The transmission line is the sum of all conductors and their ground loops.
6. What is impedance?
Impedance is the ratio of the input voltage to the input current on the transmission line (Z0=V/I). When a source sends a signal to the line, it will block it from driving until 2*TD, the source does not see it change, here the delay of the TD line (delay).
7. What is reflection?
Reflection is an echo on the transmission line. A portion of the signal power (voltage and current) is transmitted to the line and reaches the load, but a portion is reflected. If the load and the line have the same impedance, the Reflections will not happen. If the load impedance is less than the source impedance, the reflected voltage is negative. Conversely, if the load impedance is greater than the source impedance, the reflected voltage is positive. Such reflections can be caused by variations in wiring geometry, incorrect wire termination, transmission through the connector, and discontinuity in the power plane.
8. What is overshoot?
Overshoot is when the first peak or valley exceeds the set voltage - the highest voltage for the rising edge and the lowest voltage for the falling edge. Undershoot refers to the next valley or peak. Excessive overshoot can cause protection of the diode to work, leading to premature failure.
9. What is undershoot (ringback)?
Overshoot is the second peak or valley that exceeds the set voltage - either excessively for the rising edge or too large for the falling edge. Excessive undershoot can cause false clock or data errors (misoperations).
10. What is ringing?
Ringing is the repeated occurrence of overshoots and undershoots. The ringing and rounding of the signal is caused by excessive inductance and capacitance on the line, the ringing is underdamped and the surrounding oscillation is overdamped. Signal integrity problems usually occur in periodic signals, such as clocks. Oscillation and surround oscillations are caused by a variety of factors, and the oscillations can be reduced by appropriate terminations, but they cannot be completely eliminated.
11. What is the settling time?
The settling time is the time required for an oscillating signal to settle to a specified final value.