Signal Integrity (Signal Integrity, SI) is the signal quality of the signal line, that is the signal in the circuit with the correct timing and voltage ability to respond. Timing, duration and amplitude of the voltage signal if the circuit can be required to reach the receiver, this circuit can be determined with a better signal integrity. Conversely, when the signal is not a normal response, there have been a signal integrity problems.
High-speed PCB signal integrity problems including signal reflection, crosstalk, signal delay and timing errors.
· Reflector: signal transmission in the transmission line, high-speed PCB when the characteristic impedance of the transmission line impedance of the signal source or load impedance mismatch, signal reflection occurs, the signal waveform overshoot, undershoot, and the resulting ringing. Overshoot (Overshoot) refers to the first peak (or valley) of signal transitions, which is above the level in the supply voltage or the reference additional effect under the ground level; punched (Undershoot) is the signal jump The next valley (or peak) change. Excessive overshoot voltage shocks often cause long-term damage to the device, undershoot will drop
Low noise tolerance, ringing increases the time needed for signal stability, thus affecting the system timing.
· Crosstalk: the PCB, the electromagnetic crosstalk is the transmission line when the signal propagation, interference due to undesired electromagnetic noise energy through the mutual capacitance and mutual inductance generated by the adjacent transmission lines, which is caused by the same type of structure region where the generated interaction. Mutual capacitance caused by the coupling current, known as capacitive crosstalk; while mutual coupling voltage trigger, called inductive crosstalk. On the PCB, crosstalk and trace lengths, the signal line spacing, as well as the status of the reference ground plane and so on.
· Signal delay and timing errors: The signal wires on the PCB with limited speed transmission, the signal emitted from the driver side to reach the receiving end, during which there is a propagation delay. Excessive signal delay or signal delay mismatch may cause timing errors and logic functions chaos.
Design analysis not only can effectively improve the performance of the product, and can shorten product development cycles, reduce development costs high-speed digital system signal integrity analysis. In the case of a digital system to a high-speed, high-density development direction, grasp this design tool has a very urgent and necessary. Model and calculation analysis on signal integrity analysis algorithms constantly improve and enhance digital system design methodology using the signal integrity design and analysis of computer will be very broad, very comprehensive application.
In short, signal integrity problems is to study high-speed digital system design issues currently facing the field. In the design methods, the design tools as well as the composition and design team collaboration, as well as ideas, designers, need to continue to improve, ensure the system works is that all engineering and technical personnel to achieve the ultimate goal.
