Did you ever experience an annoying humming sound emanating from the sound system? Typically, the noise results from alternating current power(energy) lines entering the audio tool. When multiple pieces of equipment in a good design are linked to a common ground via different paths, a ground loop is formed. This loop makes a pathway for current to flow between various equipment grounds & back, ultimately resulting in humming caused by the current flow through an audio tool ground.
This article aims to examine the concept of the ground loop and provide insights into effective elimination methods.
The Need for Ground Loop PCB
Circuits or Devices without grounding can lead to problems caused by significant static charges. In an ungrounded system, insulation leakage can cause the accumulation of substantial fixed amounts, posing a significant risk of electric shock when coming into contact with such circuits. If a conductor is at a lower potential, the likelihood of high static charges discharging and resulting in ampere currents flowing, which harms the system, is relatively high. Grounding can ensure the security of both the user & the tool.
Ideal Ground Loop PCB
For electrical circuits to have current flow, a closed path must be present. This fast-path requires a return way for a current to move back to a source, facilitated by the common point referred to as “ground” in boards.
In an ideal scenario, ground connections have zero resistance & parasitic capacitance. The circuit elements are linked to the ground & presumed to possess identical potential. In such cases, the potential difference in absence in the environment avoids current flow. But it is not feasible in practical applications.
In reality, the notion of a common ground potential is often only applicable in theory or on paper. The presence of non-ideal factors, such as the parasitics and resistance of the wires, results in a variance in ground potential, leading to circulating current flow. These non-idealities are responsible for the potential ground difference.
What Is a Ground Loop PCB?
If there are conducting paths that link more than two points in the electrical system, typically at ground potential, a ground loop is established. Such grounds having various ground potentials can be problematic since it causes potential differences and currents to move between floors via a coil.
Ground Loop PCB Formation in Circuits
Ground loops can form in circuits through various means, including:
- If we take the example of the shielded cable where a drain wire is linked to the ground at both ends, a ground link is already established by the conductor. Since two wires are attached to the bottom of the shielded cable, two linked paths are formed, creating the ground loop. The circulating currents in a coil are dependent on the wire parameters.
- During the installation of electrical equipment, device grounding & structure grounding of or foundation where the equipment is installed are implemented. However, if two pieces of electrical equipment are grounded using the same cable, and the form is grounded directly, it leads to two paths that result in the ground loop.
- Conductors, power lines, or communication equipment are often linked to the ground. However, if the cables are connected to & the same endpoint, they shape the ground loop.
Effects of Ground Loop PCB
Ground loops cause many problems, including:
- A ground loop works as the antenna, capturing electromagnetic energy & causing noise/interference that disrupts the signal quality.
- An antenna effect loop can generate surges that may potentially damage electronic components & circuits.
- Current leakage that flows between equipment sharing a common ground can lead to harmful effects on elements & measurement systems.
- The dynamic variety of digital signals may decrease due to ground voltage offsetting, which can increase the susceptibility of digital signals to interference, thereby negatively impacting digital communication.
The ground connection in a circuit serves as the primary return path for the current flow and as a reference point for measuring potential across different topics. Ground signals/traces occupy a significant portion of a printed circuit board. So, Improper grounding results in issues like coupling, ground loops, and electromagnetic noise interference, which can adversely affect the circuit
· Ground Plane:
Using a ground plane is a popular and effective technique for establishing proper grounding in PCB boards. A ground plane refers to a large area of copper that serves as a return path for current from various points on the PCB. This provides a low-impedance way for current & acts as the heat sink. Additionally, it helps to reduce crosstalk from interference.
Designers typically place the ground plane on the bottom layer and other signals on the top coating when designing a two-layer PCB. While a few calls may be routed in the ground plane, we recommend keeping the number of signal tracks in the ground plane to a minimum.
For Four layer PCBs, we recommend dedicating a whole layer solely for grounding & avoid placing any signal collection in that layer. Adding signal traces in the ground layer can result in a problem known as a ground loop.
Occurs when current flows in a circular path due to the traces on the PCB. In an ideal printed circuit board. All points in the ground at equal potential. But in reality, the resistance tends to change across different topics even though they are all part of the ground plane.
When a ground loop is present, it causes the current to bounce back & forth within the circle, creating issues in the PCB design. To prevent ground loops, it is essential to understand the current movement in the circuit and avoid making loop-forming traces.
One way to eliminate the ground loop is by using vias to link with other coatings, especially if the ground plane is present. This approach helps to establish a continuous ground connection between layers and avoids the formation of circular paths for current flow.
· Ground Connectors:
PCB boards often have more ground pins than necessary to prevent impedance mismatch when connecting to other PCBs. The mismatch in impedance can cause current flow oscillations.
To prevent oscillation, it is advisable to allocate 30_40 % of the pins on your printed circuit board connector for ground connections. By including multiple pins, you can offset impedance mismatch & establish additional paths for current.
· Isolate Grounds
When dealing with mixed signals (Analog & Digital), things can become challenging. Analog signals are highly susceptible to noise, while digital signals are inherently noisy. Therefore, it is crucial to maintain the integrity of the Analog signal by isolating the Analog ground way from the Digital signal bases in such situations.
Typically, Digital and Analog grounds are isolated by creating separate sections for each and then connecting their respective ground planes at a single ordinary point. However, there are various other methods for isolating Analog & Digital lines. It is advisable to choose the one that best suits your application & board space.
A typical approach in PCB design involves connecting a capacitor from the energy trace to a ground trace. This technique is primarily employed to ensure stable power delivery to the ICs on the board, thereby minimizing power supply noise.
In addition, this technique serves as an effective grounding method. By incorporating a decoupling capacitor, it mitigates noise that may occur between the power _ and ground paths and prevents EMI interference. We recommend adding the capacitor to each IC on the board, and positioning it as close as possible.
Utilize capacitors with the same high capacitance for all chips on the board.
To ensure optimal performance of the manufactured PCBs, there are several widely-used grounding techniques in PCB design. Speaking of printed circuit board fabrication, JLCPCB is a top-tier PCB manufacturer on a global scale. Their team of designers carefully verifies every design they receive to ensure the highest level of quality. It’s worth giving them a try.
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We hope that these tips have proven useful to you. Please feel free to share your thoughts & suggestions in our comments section below. So If you are aware of other techniques, please do not hesitate to let us know. We would happily update the article with any new and relevant information.