What is the difference between esd and emi

The continuous, low impedance shield is an absolute requirement to achieve this. Actually, a shield may be required by some regulations, like does the FCC Part If a metallic shield is not possible, at least the electronic device must be contained within an enclosure to protect it from direct contact ESD on most of its surface.

On one hand, it completely spoils this very nice tech-look, but on the other hand, it may save your day when you spill a beverage on it! If you don't have a metallic enclosure, you're a bit more pressed for options. A circuit board with solid ground plane is as good a substitute as you can get.

Having a solid ground plane helps a lot to reduce EMI emissions by reducing the distance between a possible perturbing signal and the ground. Having a continuous ground plane also helps to evacuate incoming EMI energy and avoid sensitive electronic chips.

Collecting EMI energy with a continuous ground plane is one thing, but this energy must be evacuated, and a proper grounding is the only solution. However, this is not always possible, like for a portable device, for example. ESD may have very nasty effects on semiconductors, and even when protected by a shield or a simple non-metallic enclosure, they may still hit the electronic device by contact or close proximity through ALL externally accessible devices: buttons, sliders, connectors, jacks, LEDs, LCD displays, loudspeaker, antennas If we try to avoid Quantum Physics altogether, it is sufficient to say that these TVS devices are a kind of avalanche diodes, that are like a small capacitance a few pF when a voltage lower than a given threshold is applied between its pins, and convert into a short when the voltage is higher.

The main characteristics of these TVS diodes are their capacitance value, threshold voltage, maximum allowed pulse voltage and duration, trigger time, and if they allow monodirectional or bidirectional current flow through them used when a signal may be negative relative to ground. For the general differential-mode coupling case, the solution is to add electronic filters that will remove all unwanted noise outside the expected frequency range.

They may be band-pass or low-pass filters, and you can find some integrated filters eventually with combined ESD protection to add to your circuit, Ferrite bead choke to clamp onto a cable, or you can make your own filter using discrete components. As explained above, common-mode interference is when a disturbing source pollutes 2 conductors with the same perturbation. In the case where the 2 conductors carry 2 differential signals that are always opposite, the perturbation can be removed almost completely using " common-mode choke ".

This is very effective for Ethernet, for example, which specifications require transformer coupling, usually with some common mode filtering to take the edge off, and a 1nF capacitor, from center tap to ground, to handle ESD. It is usually combined with Bob-Smith termination resistors for the cable side, and 50 ohm termination resistor for the PHY device side. The only reason to follow opinion 1 would be to avoid ground loops by connecting the shield on both side to grounds at different levels, but because USB cables are so short, ground loops aren't really much of an issue.

Opinion 2 will actually work, even when exposed to EMI and won't radiate itself. The downside is, all that EMI is conducted over your board's ground, and will find its way out any cables attached to it. The problem is that this system does not deal with ESD , which has no path to ground. I have seen such ferrite beads melted by a distant lightning strike! An ESD event can have a fast rise time, especially for low voltage discharges [5]. This electromagnetic radiation EM can readily couple to circuit traces conductors acting as antennae.

For ungrounded conductors coupled within a capacitive circuit, this EM wave can induce a static charge, building until a discharge, breakdown, recombination or neutralisation occurs.

High-speed circuits, by their nature, tend to be very susceptible to high-frequency signals such as those from a nearby ESD event. It is important to note that the arc length of an ESD is of greater influence to its disturbance than its voltage [7]. An Electromagnetic Interference EMI is an unwanted electromagnetic energy, whether intentionally or unintentionally generated , of almost any frequency and energy level.

EMI is defined to exist when undesirable voltages or currents are present to adversely influence the performance of an electronic circuit or system. An EMI, or summation of EMIs, can over time induce a charge static voltage on an ungrounded conductor coupled in a capacitive circuit, i. A high energy ESD can drive a substantial EMI energy to couple and charge passive circuits or energise active circuits with significant system problems. EMC practices involving shielding designs typically account for EMI from known sources, but should also consider unplanned sources such as ESD events in the near vicinity of the active or sensitive system s.

Tonoya, K. Watanabe, and M. If there is excess electrical charge within the circuit, that charge could attempt to find somewhere else to go, if not for the limiting power of the shield. A proper ESD shield will dissipate the electrical charge so that is is removed safely. Electromagnetic interference, which is represented as EMI, is concerned with electromagnetic radiation.

If the environment temperature is too high, equipment can overheat. If the humidity level is too low, the chance of ESD increases. If the humidity level is too high, equipment can suffer from moisture damage. Electrostatic Discharge Electrostatic discharge ESD , harsh climates, and poor-quality sources of electricity can cause damage to computer equipment. Follow these recommendations to help prevent ESD damage: Keep all components in antistatic bags until you are ready to install them.

Use grounded mats on workbenches. Electromagnetic Interference Electromagnetic interference EMI is the intrusion of outside electromagnetic signals in a transmission media, such as copper cabling. There are many sources of EMI: Any source designed to generate electromagnetic energy Man-made sources like power lines or motors Natural events such as electrical storms, or solar and interstellar radiations Wireless networks are affected by radio frequency interference RFI.