System Grounding
Definition
In the context of a circuit, ground is the reference voltage point typically designated as 0V, serving as a common reference for voltage measurements.
In Practical Design
Ground is not merely a single point with a fixed voltage of 0V. In practical circuits, it functions as the lowest impedance path for the return of electrical current. The ground plane inside a printed circuit board (PCB) consists of a large, continuous copper plane designed to provide a low-resistance path for current flow.
It's important to note that ground potential can vary at different points along the ground plane due to voltage distribution influenced by circuit behavior. Additionally, the path taken by DC current is determined by the principle of least resistance, favoring the widest and shortest path available.
On the other hand, AC current follows the path of least impedance, which corresponds to the shortest current loop to minimize induced noise and maintain signal integrity.
Star Connection and Single Point Grounding
One common technique used in circuit design to minimize interference between analog, digital, and power systems is star grounding.
Star grounding involves the partitioning of ground connections into separate paths for analog, digital, and power components, with each path converging at a single point called the star point. The star point is typically located near the power supply or ground plane.
By separating the ground paths, the goal is to prevent the coupling of noise and interference between different system components. This approach helps to maintain the integrity of sensitive analog signals by minimizing the introduction of noise from digital or power systems.
In a star grounding scheme, analog, digital, and power components are connected to their respective ground paths. The ground paths are then connected at the star point, creating a centralized reference for all systems. This configuration reduces the likelihood of ground currents from one system interfering with the ground currents of another system.
Care must be taken when implementing star grounding to ensure proper layout and routing of ground connections. It is important to minimize ground loops, which can introduce unwanted noise and potential differences between different parts of the circuit. Proper grounding techniques, such as keeping ground traces short and avoiding shared ground paths, can help achieve the desired isolation between analog, digital, and power systems.
Summary
By utilizing star grounding in the partitioning of ground connections, designers can effectively manage noise and interference, enhancing the overall performance and reliability of the circuit, particularly in systems where analog signals require high fidelity and minimal distortion.