3. GROUNDING CONNECTION

An appropriate grounding can resolve a lots of interferences' problems therefore is convenient already in the project phase to study the best mode to grounding a circuit. There are two "earths":

1. safety earth (for the frame, the wrapper etc.)
2. signal earth (for the signals currents)

The signal earth represents the reference potential for the signals in the game and must be the impedance as lowest as possible (ideally zero), to maintain fix the reference potential for all the circuits at its connected.
The circuits' grounding can be made:

• Connecting the singles earths to a single point.
• Connecting the singles earths between them in sequence and then in a single point .
• Connecting the singles earths in more points (for example in more points of a diffusl level).

The a), b) modes are easy to realize but because of conductors length are valid the low frequencies (until 1MHz).
The a) mode is better because it isn't a pairing between the singles earths.
The c) mode is valid to the high frequencies because the soles connections made on a diffused ground level are too shorts and therefore at lowest inductance.
In this printed circuit is good that the different circuits to have separated earths which then flow together in a common point in the proximity of the lines grounding connectors.
The different circuits are those at low signal until those of potency, those analogical to those digital, etc
The cables screen, if it is involved to low frequencies, is connected to the earth in just a point to reduce the magnetics interferences and not for scroll on the screen the currents at 50Hz. To high frequencies the screen is grounded to the both sides.