An Introduction to Ground: Earth Ground, Analogue & Digital Ground
"Ground" is one of the most common terms in the electrical and electronics field. It has a critical role in controlling what happens when an accidental fault occurs in electrical systems. "Grounding" is an important aspect of electronic system design for both safety and electromagnetic compatibility. It also helps engineers and system designers to effectively manage undesirable radiated emissions.
What is Ground in Electronic Circuits?
In simple words, we can define ground as a zero-volt reference point in an electrical or electronic circuit. This means it has a voltage of 0 V, and all voltage measurements are relative to this reference because voltage is a value between two points in a circuit. The ground has many standard symbol representations as shown in the following picture. The most common one is the first symbol on the left.
In AC power systems, many people get it wrong by thinking that the ground and current return wire are the same. In fact, this is not true and they are two separate functions and not generally compatible. This is because significant currents flowing in a conductor prevents it from being a reliable reference potential. Also, the Ground is NOT a path for returning currents to their source. The concept of ground plays a critical role in design for safety and design for electromagnetic compatibility.
Usually, when mentioning that a point has a specific value of voltage, this means the difference of voltage between that point and the ground. However, not all voltage measurements are a reference to the ground, and it may be between any two points in the circuit. We will discuss in this article the Earth Ground, Digital Ground, and Analog Ground.
Grounding is sometimes called earthing, and exactly as the name, it means connecting the system physically and electrically to the earth with a conductive medium. This conductor could be in the form of aluminum, aluminum alloy or copper.
According to the National Electrical Code (NEC), a true earth ground should ideally be submerged a minimum depth of 8 feet (around 2.5 meters) deep into the ground using a conductive pipe or rod.
All power outlets in the buildings connect to the ground through non-current wires, usually green and yellow wires. To achieve this, we can use a breaker box and connect it with the grounding rods, then distribute the wires from the breaker box. This should connect to any metal throughout the building such as plumbing pipes or building steels.
All devices and electrical with a substantial exposed metal surface typically require connecting with the earth ground to ensure preventing unsafe potential electrical damage. This is why appliances like microwaves, games consoles, power tools have a 3-pin plugin, one of which is used for earth for the reason named above. When a fault causes a shortage between the main power and the exposed metal, the breaker box will draw a large amount of current through the ground connection, triggering the circuit breaker to open and cut off the power from the appliance.
In many cases, the earth ground symbol has different meanings for different people and is often confusing to people not in the profession. In fact, the grounding symbol is also used for referring to the common ground or 0V reference, which isn't always connected to the earth ground. The following picture demonstrates different usage for the ground symbol.
Analog and Digital Ground
Both analog and digital circuits generate noises and spikes. This happens when digital signals change their state, or change the load current in analog signals. In this case, it is better to separate digital and analog ground for mixed-signal systems. This will separate the "high-noise" digital currents from the "low-noise" analog currents. And as a result, reduce the potential of generating noises in circuits due to ground currents.
Besides, when a current flow through the ground path, a voltage variation will be generated causing a noise in the system. Such noise can affect sensitive signals in the local systems. This was why grounding is a major challenge for design and testing engineers.
There are many possible grounding approaches in the mixed-signal systems. One popular technique in some cases is the "star" ground, where all voltages in a circuit are referred to a single ground point. In reality, it may be very hard to implement this solution for some complex design although it looks simply. Another technique that may be used in similar cases is using ground bus bar.
Ground is big topic and often confuse people outside the profession. This article has only covered the basics and we hope it sheds some light on earth, common and analog and digital ground.
Published: January 21, 2021