USB CONNECTOR

USB Connector

USB stands for ‘Universal Serial Bus’ and is the next step in creating a computer interface that really works universally. It boasts cross-platform compatibility for Macintosh, Linux/UNIX, and all versions of Windows since 98SE. Universal Serial Bus (USB) is a serial bus standard to interface devices. It was designed for computers such as PCs and the Apple Macintosh, but its popularity has prompted it to also become commonplace on video game consoles, PDAs, cellphones; and even devices such as televisions and home stereo equipment (e.g., mp3 players), and portable memory devices.

The radio spectrum-based USB implementation is known as Wireless USB.

Types Of USB Connector

There are several types of USB connectors, and some have been added as the specification has progressed. For the most part, there are two types of connectors on USB cables: a long, flat rectangle for plugging into computers and hubs called 'USB-A', and a smaller, square connector for plugging into devices like external CD and Hard drives, scanners, and printers called 'USB-B'. Additionally, smaller devices such as cameras, camcorders, PDA's, and cell phones often don't have the space for a full-sized USB-B port, so they instead use a smaller trapezoidal connector called a 'Mini-B'. As if this weren't enough, Sony has also decided to make it's own USB connections, called a USB 4-pin Mini-B, which are two variations of an extremely small squarish connector found on some digital cameras.

From the original USB specification:

1- Series 'A' plug
2- Series 'A' receptacle
3- Series 'B' plug
4- Series 'B' receptacle

Added in USB 2.0 specification:

1- Mini-B plug
2- Mini-B receptacle

Added in the On-The-Go Supplement to the USB 2.0 Specification:

1- Mini-A plug (white)
2- Mini-A receptacle (white)
3- Mini-AB receptacle (grey)

Adapters, also from the On-The-Go Supplement to the USB 2.0 Specification:

1- Mini-A receptacle to Standard-A plug
2- Standard-A receptacle to Mini-A plug

Design of a USB Connector

The connectors which the USB committee specified were designed to support a number of USB's underlying goals, and to reflect lessons learned from the varied menagerie of connectors then in service. In particular:

The connectors are designed to be robust. Many previous connector designs were fragile, with pins or other delicate components prone to bending or breaking, even with the application of only very modest force. The electrical contacts in a USB connector are protected by an adjacent plastic tongue, and the entire connecting assembly is further protected by an enclosing metal sheath. As a result USB connectors can safely be handled, inserted, and removed, even by a small child. The encasing sheath and the tough moulded plug body mean that a connector can be dropped, stepped upon, even crushed or struck, all without damage; a considerable degree of force is needed to significantly damage a USB connector. It is difficult to incorrectly attach a USB connector. Connectors cannot be plugged-in upside down, and it is clear from the appearance and kinesthetic sensation of making a connection when the plug and socket are correctly mated. However, it is not obvious at a glance to the inexperienced user which way round a connector goes, so it is often necessary to try both ways. The connectors are particularly cheap to manufacture. The connectors enforce the directed topology of a USB network. USB does not support cyclical networks, so the connectors from incompatible USB devices are themselves incompatible. Unlike other communications systems (e.g. RJ-45 cabling) gender-changers are never used, making it difficult to create a cyclic USB network. The connector construction always ensures that the external sheath on the plug contacts with its counterpart in the receptacle before the four connectors within are connected. This sheath is typically connected to the system ground, allowing otherwise damaging static charges to be safely discharged by this route. This means of enclosure also means that there is a (moderate) degree of protection from electromagnetic interference afforded to the USB signal while it travels through the mated connector pair (this is the only location when the otherwise twisted data pair must travel a distance in parallel). In addition, the power and common connections are made after the system ground but before the data connections. This type of staged make-break timing allows for safe hot-swapping and has long been common practice in the design of connectors in the aerospace industry.
The USB standard specifies relatively low tolerances for compliant USB connectors, intending to minimize incompatibilities in connectors produced by different vendors (a goal that has been very successfully achieved). Unlike most other connector standards, the USB spec also defines limits to the size of a connecting device in the area around its plug. This was done to avoid circumstances where a device complied with the connector specification but its large size blocked adjacent ports. Compliant devices must either fit within the size restrictions or support a compliant extension cable which does. However, the mechanical layer has changed in some examples. For example, the IBM UltraPort is a proprietary USB connector located on the top of IBM's laptop LCDs. It uses a different mechanical connector while preserving the USB signaling and protocol. Other manufacturers of small items also developed their own small form factor connector, and a wide variety of these have appeared. For specification purposes, these devices were treated as having a captive cable.

An extension to USB called USB On-The-Go allows a single port to act as either a host or a device - chosen by which end of the cable plugs into the socket on the unit. Even after the cable is hooked up and the units are talking, the two units may "swap" ends under program control. This facility targets units such as PDAs where the USB link might connect to a PC's host port as a device in one instance, yet connect as a host itself to a keyboard and mouse device in another instance. USB On-The-Go has therefore defined two small form factor connectors, the Mini-A and Mini-B, and a universal socket (Mini-AB), which should stop the proliferation of proprietary designs.

Wireless USB is a standard being developed to extend the USB standard while maintaining backwards compatibility with USB 1.1 and USB 2.0 on the protocol level.

The maximum length of a USB cable is 5 meters; greater lengths require hubs. USB Connections can be extended to 50M over CAT5 or up to 10KM over fiber by using special USB Extender products developed by various manufacturers.

Limitations Of USB

Every product has a weakness, and even an interface as praised as USB has its downsides. One such problem is a streamline effect that occurs because of the Plug-N-Play nature of USB: devices such as keyboards and mice require constant interface with the computer, so they need to have their own dedicated USB port. They can usually be streamlined together, as with the Macintosh mice that stream through the keyboards, but they will only cause problems on hubs and other ‘sharing’ type of situations.

The most aggravating limitation of USB is the length restriction. Because of the nature in which data is carried through the cable, USB has an accepted maximum length of 15 feet. Some devices, depending on power needs and data bandwidth, may be able to go beyond this, but there are no guarantees.

The only practical solution, aside from using a different interface, is the use of repeater extension cables to fill the gaps. These cables have a small booster at the end, which reads and re-sends the signal instead of just passing it along. They can be strung along in a row, and so long as there is never more than 15 feet of cable between boosters, it is possible to run USB up to an extended maximum of 80 feet. This can get expensive, however, and alternatives are most often recommended.

AMP Connector

Amphenol Corporation is one of the world's leading producers of electronic and fiber optic connectors, cable and interconnect systems.

An Amphenol connector is often referred to as a Telco connector. AMP (short for Amphenol) connectors are most commonly seen today where a twenty-five (25) pair cable connects to an RJ-21X in a telephone room. Amphenols are male or female. Often used to link PABX's to a mainframe. An AMP Connector is a tool used to join the loose ends of a multi-pair cable into the plug ended. The AMP Champ is a "butterfly" on which the colored wire pairs in a multi-pair cable are layed out in a defined order on one side of the tool. The AMP connector is mounted on the other side. A pull lever crimps the wire ends into the pins of the AMP connector.

Coaxial Connector (Coax Connector)

Coaxial Connector or Coax Connector is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer. It is used as a high-frequency transmission line to carry a high-frequency or broadband signal. Sometimes DC power (called bias) is added to the signal to supply the equipment at the other end, as in direct broadcast satellite receivers. Because the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors, it cannot interfere with or suffer interference from external electromagnetic fields.

Coaxial Connector (coax connector) may be rigid or flexible. Rigid types have a solid sheath, while flexible types have a braided sheath, both usually of thin copper wire. The inner insulator, also called the dielectric. The dielectric may be solid or perforated with air spaces. Connections to the ends of coaxial cables are usually made with RF connectors.

From the signal point of view, a connector can be viewed as a short, rigid cable. The connector usually has the same impedance as the related cable and probably has a similar cutoff frequency although its dielectric may be different. High-quality connectors are usually gold or rhodium plated, with lower-quality connectors using nickel or tin plating. Silver is occasionally used in some high-end connectors due to its excellent conductivity, but it usually requires extra plating of another metal since silver readily oxidizes in the presence of air.

One increasing development has been the wider adoption of micro-miniature coaxial connector (coax connector) in the consumer electronics sector in recent years.