Beatrice Lang
Electrical termination is a process that involves installing a device at the end of a bus or transmission line to prevent signals from reflecting back. This device, known as a terminator, is designed to match the impedance of the cable, thereby minimising signal reflections and power losses. The terminator is typically placed at the end of a transmission line or daisy chain bus and can also be placed at the driving end of the wire or cable if it is not part of the signal-generating equipment. The main types of terminators include chip, coaxial, SCSI, and waveguide terminators, each serving a specific function. Proper electrical termination is crucial to prevent issues such as interference, distortion, and power loss in various systems.
Characteristics and Values of Electrical Termination
| Characteristics | Values |
|---|---|
| Definition | The practice of ending a transmission line with a device that matches the characteristic impedance of the line |
| Purpose | To prevent signals from reflecting off the end of the transmission line and causing interference or power loss |
| Installation | At the end of a bus or transmission line |
| Types | Chip, coaxial, SCSI, waveguide, solder, crimp, source (driver), load (receiver) |
| Standards and Certifications | EU: RoHS, ELV, and WEEE. US: FCC or Underwriters Laboratory. Canada: Canadian Standards Association (CSA) |
| Power | End termination dissipates a lot of power and requires a driver with more current sourcing capacity |
| Solder Termination | Requires stripping off wire insulation and applying flux and solder to connect the wire to the device |
| Crimp Termination | Utilized when a specific appliance or device requires direct contact with the cable; forms a powerful connection with a crimp tool and specific connectors |
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What You'll Learn
- Electrical terminators are placed at the end of a bus or transmission line
- Terminators prevent signals from reflecting back and causing interference
- The value of the resistor depends on the impedance of the line
- There are four basic types of electrical terminations: chip, coaxial, SCSI, and waveguide
- Standards and certifications: Products sold in the EU must comply with RoHS, ELV, and WEEE directives
Electrical terminators are placed at the end of a bus or transmission line
Electrical terminators, also known as electrical terminations, are placed at the end of a bus or transmission line to prevent signals from reflecting back. These reflections can cause interference and power loss. This is particularly important when working with transmission lines and high-frequency signals.
Electrical terminators are devices that match the characteristic impedance of the line. This prevents signals from reflecting off the end of the transmission line, which can cause distortion and interference. Reflections in analog signal systems can cause video ghosting, for example. In digital systems, reflections can produce ambiguous digital signal levels and cause the misoperation of digital systems.
The terminator is usually placed at the end of a transmission line or daisy-chain bus. It is designed to match the AC impedance of the cable to minimize signal reflections and power losses. The value of the resistor used in the terminator depends on the impedance of the line. If the impedance is not matched correctly, too much power will be reflected, causing all the computers on the bus to lose network connectivity.
There are two main types of termination: source (driver) termination and load (receiver) termination. Source termination involves adding a series resistor to the source to match the characteristic impedance of the transmission line. Load termination involves placing a resistor in parallel between the signal and the ground, with a value that matches the characteristic impedance of the line.
Overall, electrical terminators are essential to ensure the proper functioning of transmission lines and buses by preventing signal reflections and minimizing interference and power loss.
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Terminators prevent signals from reflecting back and causing interference
In electronics, electrical termination is the practice of ending a transmission line with a device that matches the characteristic impedance of the line. This device is called a terminator. Terminators are designed to prevent signals from reflecting off the end of the transmission line and causing interference.
When an electrical signal reaches the end of an unterminated line, it encounters an impedance mismatch, causing part of the signal to reflect back towards the source. These reflections can interfere with subsequent signals, leading to distortion and potential data errors. Radio frequency currents tend to reflect from discontinuities in the cable, such as connectors and joints, and travel back down the cable toward the source, causing interference as primary reflections. Secondary reflections can also occur at the cable starts, allowing interference to persist as repeated echoes of old data. These reflections also act as bottlenecks, preventing the signal power from reaching the destination.
To prevent this, terminators are installed at the end of a bus or transmission line. They are designed to match the AC impedance of the cable and hence minimize signal reflections and power losses. The terminator absorbs the signal energy, preventing it from being reflected back. By matching the line's impedance, terminators effectively eliminate signal reflections, ensuring signal stability and integrity. This is known as impedance matching.
In wireless communication systems, RF terminators are used to terminate unused ports to prevent signal reflections and interference. They are also used in antenna systems to terminate unconnected antenna ports, ensuring signal transmission quality and system efficiency.
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The value of the resistor depends on the impedance of the line
Electrical termination is the practice of ending a transmission line with a device that matches the characteristic impedance of the line. This device, called a terminator, is designed to match the AC impedance of the cable and minimise signal reflections and power losses.
The value of the resistor used in the terminator depends on the impedance of the line. Impedance is the ratio of the complex representation of the sinusoidal voltage between its terminals to the complex representation of the current flowing through it. It is measured in ohms and can be calculated by measuring the magnitude of voltage and current, and the phase difference between them. The impedance of a device can also be calculated by applying a sinusoidal voltage to the device in series with a resistor and measuring the voltage across the resistor.
In a two-terminal circuit, the impedance acts just like resistance, giving the drop in voltage amplitude across an impedance. In this case, the resistor value is equal to the impedance value. However, in multiple-port networks, the two-terminal definition of impedance is inadequate, and the complex voltages at the ports and the currents flowing through them are linearly related by the impedance matrix.
The impedance of a transmission line cable affects the performance of the cable. If the impedance is not matched correctly, reflections can occur, causing interference and power loss. The value of the resistor in the terminator must be chosen to match the impedance of the line to minimise these reflections and ensure optimal performance.
Different types of terminators use resistors with different values depending on the specific application. For example, a 10BASE2 network requires a 50-ohm BNC terminator, while a Controller Area Network (CAN Bus) uses a 120-ohm resistor.
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There are four basic types of electrical terminations: chip, coaxial, SCSI, and waveguide
In electronics, electrical termination is ending a transmission line with a device that matches the characteristic impedance of the line. This prevents signals from reflecting off the end of the transmission line, which can cause distortion and interference.
Electrical termination can be applied in four basic types: chip, coaxial, SCSI, and waveguide.
Chip
On-die termination (ODT) is a technology where the termination resistor for impedance matching in transmission lines is located inside a semiconductor chip instead of on a printed circuit board (PCB). This technique reduces the number of resistor elements and complex wiring on the motherboard. It is implemented with several combinations of resistors on the DRAM silicon along with other circuit trees.
Coaxial
Coaxial termination is used to maintain signal integrity in coaxial cable setups. Impedance matching is important in coaxial terminations to prevent signal reflection and potential damage to the source. Coaxial terminations can also improve noise reduction.
SCSI
SCSI (Small Computer System Interface) terminators are used in storage and backup systems. They are designed to match the AC impedance of the cable to minimize signal reflections and power losses. Active terminators, a type of SCSI terminator, have a built-in voltage regulator to compensate for variations in terminator power.
Waveguide
Waveguide terminations absorb energy and prevent RF signals from reflecting back from open-ended or unused waveguide ports. They are passive devices that dissipate radio frequency (RF) energy by producing heat energy. Waveguide terminations are designed to operate over a specific frequency range and have specific performance specifications, such as voltage standing wave ratio (VSWR) and return loss.
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Standards and certifications: Products sold in the EU must comply with RoHS, ELV, and WEEE directives
In electronics, electrical termination is ending a transmission line with a device that matches the characteristic impedance of the line. This prevents signals from reflecting off the end of the transmission line, which can cause distortion and interference.
Standards and Certifications
Products sold in the EU must comply with the following directives:
RoHS Directive
The Restriction of Hazardous Substances (RoHS) Directive restricts the use of ten substances in electrical and electronic equipment: lead, cadmium, mercury, hexavalent chromium, polybrominated biphenyls (PBB), polybrominated diphenyl ethers (PBDE), and certain phthalates. The directive aims to protect human health and the environment by preventing the risks associated with electronic and electrical waste.
ELV Directive
The End-of-Life Vehicles (ELV) Directive sets targets for the reuse, recycling, and recovery of end-of-life vehicles and their components. It also prohibits the use of hazardous substances, such as lead, mercury, cadmium, and hexavalent chromium, in the manufacturing of new vehicles. The directive aims to improve the environmental performance of all economic operators involved in the life cycle of vehicles.
WEEE Directive
The Waste from Electrical and Electronic Equipment (WEEE) Directive addresses the rapidly increasing amount of waste electrical and electronic equipment (e-waste) generated in the EU. This directive promotes the collection, treatment, and recycling of e-waste, which includes mobile phones, computers, household appliances, and medical devices. By improving the management of e-waste, the directive aims to increase resource efficiency and support a circular economy.
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Frequently asked questions
Electrical termination is ending a transmission line with a device that matches the characteristic impedance of the line to prevent signals from reflecting off the end of the transmission line.
Electrical termination is important because it prevents signals from reflecting off the end of the transmission line, which can cause distortion and interference.
There are two main methods of electrical termination: soldering and crimping. Soldering involves stripping off the wire insulation and applying flux and solder to connect the wire to the device. Crimping involves using a crimp tool with specific connectors to form a strong connection.
