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Two methods to connect digital ground and analog ground
Common sense in SMT process

Why do we need to introduce so many subdivided GND

Engineers may ask, how can there be so many distinctions between grounds, and how can a simple circuit problem be so complicated?

Why do we need to introduce so many subdivided GND functions?

Generally regarding this type of GND design problem, Engineers simply named GND uniformly, and did not distinguish it during the schematic design process, which makes it difficult to effectively identify the GND ground of different circuit functions when PCB layout, directly and simply Connect all GND ground s together.

Although this operation is simple, it will lead to a series of problems:

1. Signal crosstalk
If the GND of different functions are directly connected together, the high-power circuit passes through the GND, which will affect the 0V reference point GND of the low-power circuit, thus causing crosstalk between signals of different circuits.

2. Signal accuracy
For analog circuits, the core indicator of its assessment is the accuracy of the signal. Without accuracy, the analog circuit loses its original functional significance.

Since the ground line CGND of the AC power supply is a sine wave, it fluctuates periodically, and its voltage also fluctuates up and down. It is not always maintained at 0V like the DC ground line GND.

Connect the GND of different circuits together. The periodically changing AC ground CGND will drive the AGND of the analog circuit to change, which affects the voltage accuracy value of the analog signal.

3. EMC experiment
The weaker the signal, the weaker the external electromagnetic radiation EMC; the stronger the signal, the stronger the external electromagnetic radiation EMC.
If the GND of different circuits are connected together, the GND of the strong signal circuit directly interferes with the GND of the weak signal circuit. The consequence is that the electromagnetic radiation EMC, which was originally a weak signal, has also become a signal source of strong external electromagnetic radiation, which increases the difficulty of the circuit pass EMC experiments.

4. Circuit reliability
Between the circuit systems, the fewer signal connections, the stronger the circuit's ability to operate independently; the more signal connections, the weaker the circuit's ability to operate independently.

Just imagine, if there is no intersection between the two circuit systems A and B, the function of the circuit system A obviously cannot affect the normal operation of the circuit system B, and the function of the circuit system B also cannot affect the circuit system A.

This is like a couple of unfamiliar men and women. Before they become lovers, the girl's mood changes will not affect the boy's mood, because they do not have any intersection.

If in the circuit system, the circuit ground of different functions are connected together, it is equivalent to increasing a link of interference between the circuits, that is, reducing the reliability of circuit operation.