Noise less Power supply

All ICs need power supply to operate. The power is supplied to the ICs using power and ground planes and using thick traces connecting to the power and ground pins of the ICs. A number of events lead to fluctuation of voltage level on the power supply and ground nets. One of the reasons can be change in the load current because of the simultaneous switching of the output pins.

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Coupling of the traces

Two nearby traces create coupling. Changing electric field due to the rate of change of voltage dV/dt, on one trace induces a capacitive coupling on a nearby trace. A changing magnetic field due to changing current dI/dt on one trace induces inductive coupling on a nearby trace. The capacitive or the inductive coupling induce undesired distortions in the form of cross talk in the nearby traces

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Timing Relationship between Signals

The signal launched at one end of the PCB trace takes finite amount of time when traveling from one end to another end of the trace. The signal typically takes 150 ps to travel 1 inch of trace. If your trace is 8 inches long, it will take 1200 ps to travel from one end of the trace to the other end. In many buses, clock and data need to preserve a definite timing relationship. If the receiver captures data at the rising edge of the clock, then the data must arrive and become stable slightly before the rising edge of the clock.
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Integrity of Point to Point Signal

When a driver launches a signal, it travels along the traces of the PCB. The traces that travel on the PCB must follow certain rules for proper operation at high speed. One of the rules they usually need to follow is that their trace width and their separation above the ground or power plane has a well defined value.
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Signal Integrity for PCB Designers - Introduction

Signal integrity refers to the quality of the signal that needs to be maintained for the receiver in an electronic design to deliver its intended goal. As the speed of the data signal increases a number of reasons lead to the degradation of the high speed signals. High speed PCB design refers to the techniques that must be followed in order for a circuit on a Printed Circuit Board to function properly when the edge rate and data rate of the signal propagating on the PCB is high.

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