PCB Grounding Plane
Each printed circuit board has a circuit ground where the return current will sink all over from the circuit. This is greatly important in signal integrity and EMC considerations.
There are many practices that make perfect system ground to ensure compliance with functional performance and regulatory requirements, but these practices are different for different applications. For example, a normal telecommunication line has a suitable grounding system of 48 to 52VDC with a tip and a ring, while in a power and pole mounted transformer, this is a voltage from about 100s to 1000s.
As long as all important critical conductors are buried in a single ground plane in the printed circuit board, the ground plane can improve signal integrity and EMC.
The bypass capacitor can provide power to significantly reduce the effect of the component's normal transient switch and load current during operation.
In a PCB board, the ground bus and voltage bus are separated from each other by series inductance and shunt capacitance. As the frequency of the PCB increases, the voltage and ground bus will oscillate due to shock excitation. This can be minimized by using a separate voltage and ground plane. These ground planes have relatively low resistance and impedance. The 35um thick copper foil has the DC solid sheet resistance of 1mohms/sq
The power supply ground is also the most important ground consideration. In many cases it is connected to the body ground of the equipment which is connected to the earth connection from 220VAC outlet. The filter capacitors connected between the power supply and the ground plane are mostly tantalum and are short-circuited in the case of electrical surges. Digital and analog ground planes are mostly separated in mixed-signal embedded systems where high-frequency digital signals are separated from low-frequency analog signals by means of opto-couplers or opti-isolators. These isolators provide insulation between the low power digital 1.5V, 3.3V or 5V circuitry from high power analog circuit like 12V, 24VDC.