1. What is Singnal Integrity? Singnal Integrity refers to the ability of a signal to produce the correct response in a circuit. The signal has good signal integrity (Singnal Integrity) refers to the voltage level value that must be reached when needed. The main signal integrity problems include reflection, oscillation, ground bounce, crosstalk, etc. Common signal integrity problems and solutions: Possible causes and solutions of the problem. Other solutions. Overshoot terminal impedance mismatch. Terminal termination. Use a slow rise time drive source. The DC voltage level is not good. The line load is too large. Replace the DC load at the receiving end, re-wiring or check the ground plane. The crosstalk is too large. The coupling between the lines is too large. Use the transmission driver with a slow rise time. Use a drive source that can provide more drive current. The delay is too large. The transmission line distance is too long. Or re-wiring, check that the serial terminal connector uses an impedance-matched driving source, change the wiring strategy, oscillation impedance does not match, and connect a damping resistor in series at the transmitting end. 2. What is crosstalk? Crosstalk (crosstalk) refers to the interaction between two different electrical properties. The crosstalk is called Aggressor, and the other one that receives interference is called Victim. Usually, a network is both Aggressor (intruder) and Victim (victim). Ringing and ground bounce are both single signal line phenomena in signal integrity problems (accompanied by ground plane loops), and crosstalk is caused by two signal lines on the same PCB board and the ground plane, so it is also called a three-wire system . Crosstalk is the coupling between two signal lines, and the mutual inductance and mutual capacitance between the signal lines cause noise on the line. Capacitive coupling induces coupling current, and inductive coupling induces coupling voltage. The parameters of the PCB layer, the signal line spacing, the electrical characteristics of the driving end and the receiving end, and the line termination method all have a certain impact on the crosstalk.
3. What is electromagnetic compatibility (EMI)? Electromagnetic interference (Ectromagnetioc Interference), or electromagnetic compatibility (EMI), is the result of antenna characteristics obtained from a transmission line (such as a cable, wire, or package pin). Printed circuit boards, integrated circuits and many cables emit and affect electromagnetic compatibility (EMI) issues. FCC defines the maximum emission level for a certain frequency (for example, in the field of flight controllers).
4. What is the difference between time domain and frequency domain? The time domain is an oscilloscope observation of a waveform. It is usually used to find out the delays, skew, overshoot, undershoot and settings from pin to pin Time (setting times). Frequency domain (frequency domain) is the observation of the spectrum analysis of a waveform, it is usually used for the observation of the waveform and the spectrum analysis, and it is usually used for comparison between the waveform and the FCC and other EMI control limits. (There is an analogy, it is like a radio-you hear it in the time domain, but you need to find your favorite station in the frequency domain.)
5. What is a transmission line? The transmission line is a network (wire), and its current returns to the ground and power source. The wires on the circuit board have electrical characteristics such as resistance, capacitance, and inductance. In high-frequency circuit design, the capacitance and inductance on the circuit board circuit make the wire equivalent to a transmission line. The transmission line is the sum of all conductors and their ground loops.
6. What is impedance (impedance)? 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 prevent it from driving until 2*TD, the source does not see its change, where TD is the line delay.
7. What is reflection? Reflection is the echo on the transmission line. Part of the signal power (voltage and current) is transmitted to the line and reaches the load, but part is reflected (reflected). If the load and the line have the same impedance, 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. Variations in factors such as wiring geometry, incorrect wire termination, transmission through connectors, and discontinuities in the power plane can all cause such reflections.
8. What is overshoot? Overshoot is the first peak or valley that exceeds the set voltage-the highest voltage for rising edges and the lowest voltage for falling edges. Undershoot (Undershoot) refers to the next valley or peak. Excessive overshoot can cause the protection diode to work, leading to premature failure.
9. What is an undershoot (ringback)? Overshoot is the second peak or valley value exceeding the set voltage-excessive valley value for the rising edge or too large peak value for the falling edge. Excessive undershoot can cause false clock or data error (misoperation).
10. What is ringing? Ringing is the repeated occurrence of overshoots and undershoots. The ringing and rounding of the signal are caused by excessive inductance and capacitance on the line. The ringing belongs to the under-damped state and the rounding oscillation belongs to the over-damped state. Signal integrity problems usually occur in periodic signals, such as clocks. Oscillation and surround oscillation are caused by many factors like reflection. Oscillation can be reduced by proper termination, but it is impossible to completely eliminate it.
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