About floating land

Signal ground
The signal ground of a device may be a point or a piece of metal in the device as the signal ground reference point, which
provides a common reference potential for all signals in the device.
There are single-point grounding, multi-point grounding, floating ground and mixed grounding. (Floating
ground is mainly introduced here) Single-point grounding means that only one physical point in the entire circuit system is defined as the ground reference point, and all other points that need to be grounded
are directly connected to this point. In low frequency circuits, there will not be too much influence between wiring and components. Usually
the circuit with frequency less than 1MHz should be grounded at one point.
Multi-point grounding means that each grounding point in the electronic device is directly connected to the ground plane closest to it (ie, the metal
bottom plate of the device ). In high-frequency circuits, the influence of parasitic capacitance and inductance is greater. Generally, circuits with frequencies greater than 10MHz often use
multi-point grounding.
Floating, that is, the ground of the circuit is connected to the earth without a conductor. 『Virtual ground: A point that is not grounded, but is at the same potential as the ground. "
The advantage is that the circuit is not affected by the electrical properties of the earth. Floating ground can make
the isolation resistance between power ground (strong ground) and signal ground (weak ground) very large, so it can prevent electromagnetic interference caused by common ground impedance circuit coupling.
The disadvantage is that the circuit is susceptible to the influence of parasitic capacitance, which makes the ground potential of the circuit fluctuate and increases
inductive interference to the analog circuit .
A compromise is to connect a large bleeder resistor between the floating ground and the common ground to release the accumulated
charge. Pay attention to control the impedance of the release resistor, too low resistance will affect the qualification of the leakage current of the equipment.
Application of floating technology
a. Separate AC power ground from DC power ground.
Generally, the neutral line of AC power is grounded. However, due to the grounding resistance and the current flowing through it, the power supply
The zero line potential of is not the zero potential of the earth. In addition, there are often many interferences on the neutral line of the AC power supply. If the AC
power supply ground is not separated from the DC power supply ground, it will affect the normal operation of the DC power supply and subsequent DC circuits. Therefore, the use
of floating technology that separates the AC power ground from the DC power ground can isolate the interference from the AC power ground.
b. Floating technology
of amplifier For amplifiers, especially small input signals and high-gain amplifiers, any small
interference signal at the input end may cause abnormal operation. Therefore, using the floating technology of the amplifier can block the entry of interference signals and
improve the electromagnetic compatibility of the amplifier.
c Precautions for floating technology
1) Try to increase the insulation resistance of the floating system to the ground, thereby helping to reduce the common mode
interference current entering the floating system .
2) Pay attention to the parasitic capacitance of the floating system to the ground. High-frequency interference signals may still be coupled
to the floating system through the parasitic capacitance .
3) Floating technology must be combined with electromagnetic compatibility technologies such as shielding and isolation to achieve better
expected results.
4) When using floating technology, attention should be paid to the harm of static electricity and voltage counterattack to equipment and humans