1. GND refers to the abbreviation of the ground terminal of the wire. It represents the ground or the 0V reference.
2. The GND (Ground) in a circuit diagram or on the PCB represents the ground wire or the 0V reference. GND is a common reference point, but it is not a direct connection to the physical earth. It is an assumed ground for the application—typically the negative terminal of the power supply. This ground is different from the earth ground and may or may not need to be connected to the actual earth, depending on the specific design requirements.
3. The signal ground of a device could be a specific point or a metal plane within the device that serves as the reference point for all signals, providing a common reference potential across the system.
4. Grounding methods include single-point grounding, multi-point grounding, floating ground, and mixed grounding.
5. Single-point grounding means that only one physical point in the entire circuit is defined as the ground reference. All other points requiring grounding are directly connected to this reference point. In low-frequency circuits, the impact of wiring and component placement is minimal. Generally, circuits with frequencies under 1 MHz should use single-point grounding.
**Multi-point grounding** refers to connecting each grounding point in an electronic device directly to the nearest ground plane (i.e., the device’s metal bottom plate). In high-frequency circuits, the effects of parasitic capacitance and inductance are more pronounced. Generally, circuits with frequencies above 10 MHz often utilize multi-point grounding.
Are you familiar with **single-point grounding**, **multi-point grounding**, **floating ground**, and **mixed grounding** in PCB layout and design?
**Floating ground** means that the circuit’s ground is connected to earth without a conductor. A **virtual ground** refers to a point that is not physically grounded but maintains the same potential as the ground.
The main advantage of floating ground is that the circuit is not affected by the electrical properties of the earth. Floating ground increases the isolation resistance between the power ground (high current ground) and the signal ground (low current ground), which helps prevent electromagnetic interference (EMI) caused by common ground impedance coupling.
However, the downside is that the circuit is more susceptible to parasitic capacitance, which can cause variations in the ground potential and increase inductive interference, especially in analog circuits.
The term “earth” is crucial in electronics, as it encompasses many types of grounds, which can be confusing. Let’s summarize the concept of “grounding.”
**Grounding** includes both the signal ground inside the device and the equipment grounding, which are different in purpose and function. The classic definition of “ground” is “the equipotential point or plane used as a reference for a circuit or system.”
1. **Signal ground**, also known as reference ground, is the point of zero potential that serves as the common reference for the circuit signals.
– **DC ground**: The reference point for DC circuits, representing zero potential.
– **AC ground**: The neutral line of AC power, which should be distinguished from the ground wire.
– **Power ground**: The reference point for high-current devices and power amplifiers.
– **Analog ground**: The reference point for analog components like amplifiers, sample-and-hold circuits, A/D converters, and comparators.
– **Digital ground**: Also known as logical ground, this serves as the reference for digital circuits.
– **Hot ground**: In switching power supplies without a power-frequency transformer, the “ground” of the switching circuit is linked to the mains power grid and is called “hot ground” because it is live.
– **Cold ground**: The output ground of a switching power supply, which is isolated by the high-frequency transformer and photocouplers, and is not live.
### Signal Ground
The signal ground in a device may be a specific point or a piece of metal that serves as the reference for all signal potentials within the device. There are different grounding schemes, including **single-point grounding**, **multi-point grounding**, **floating ground**, and **mixed grounding** (with floating ground being the primary focus here).
– **Single-point grounding** means that one physical point in the entire circuit system is defined as the reference ground. All other points requiring grounding are connected directly to this reference point. In low-frequency circuits, the wiring and component interactions are minimal. Typically, circuits operating below 1 MHz use single-point grounding.
– **Multi-point grounding** means that each grounding point in the device is directly connected to the nearest ground plane (usually the metal bottom plate of the device). In high-frequency circuits, the impact of parasitic capacitance and inductance becomes more significant. Circuits with frequencies above 10 MHz typically use multi-point grounding.
– **Floating ground** refers to a ground that is not physically connected to earth but instead has the same potential as ground. This approach offers the advantage of preventing the circuit from being influenced by earth’s electrical properties. Floating ground can increase the isolation resistance between power ground (strong current) and signal ground (weak current), thus reducing the risk of electromagnetic interference due to common ground impedance coupling.
However, the main disadvantage is that the circuit becomes more sensitive to parasitic capacitance, which can alter the ground potential and contribute to inductive interference in analog circuits.
One compromise solution is to use a large bleeder resistor between the floating ground and common ground to dissipate accumulated charge. Care must be taken to control the impedance of the bleeder resistor, as too low a resistance can affect the leakage current qualification of the device.
### 1. Applications of Floating Technology
**a. Separation of AC and DC power grounds**
Typically, the neutral line of the AC power supply is grounded. However, due to grounding resistance and current flow, the neutral line’s potential is not exactly the earth’s zero potential. Additionally, the AC power neutral often carries interference. If the AC power ground is not isolated from the DC power ground, this can impact the operation of DC circuits. Using floating technology to separate the AC and DC grounds helps isolate AC noise from the DC system.
**b. Floating technology for amplifiers**
For amplifiers—especially those handling small input signals and requiring high gain—even small interference signals at the input can cause malfunction. Floating the amplifier ground helps block unwanted signals and improves the electromagnetic compatibility (EMC) of the amplifier.
**c. Considerations when using floating technology**
1) Increase the insulation resistance of the floating system to the ground, which helps reduce common-mode interference currents.
2) PCB manufacturers must consider the parasitic capacitance between the floating system and the ground. High-frequency interference signals may still couple into the floating system via parasitic capacitance.
3) Floating technology should be used in conjunction with electromagnetic compatibility techniques like shielding and isolation for optimal performance.
4) When implementing floating technology, precautions should be taken to prevent static electricity or voltage backfeed from damaging equipment or posing risks to users.
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