Universal-Serial-Bus (USB) has been widely deployed as a standard bus for connecting peripherals such as digital cameras and music players to personal computers (PCs) and other devices. Currently, the top transfer rate of USB is 480 Mb/s, which is quite sufficient for most applications. Faster serial-bus interfaces are being introduced to address different requirements. PCI Express, at 2.5 Gb/s, and SATA, at 1.5 Gb/s and 3.0 Gb/s, are two examples of high-speed serial bus interfaces for the next generation devices, as are IEEE 1394 and Serial Attached Small-Computer System Interface (SCSI).
FIG. 1A shows a prior-art peripheral-side USB connector. USB connector 10 may be mounted on a board in the peripheral. USB connector 10 can be mounted in an opening in a plastic case (not shown) for the peripheral. USB connector 10 contains a small connector substrate 14, which is often white ceramic, black rigid plastic, or another sturdy substrate. Connector substrate 14 has four or more metal contacts 16 formed thereon. Metal contacts 16 carry the USB signals generated or received by a controller chip in the peripheral. USB signals include power, ground, and serial differential data D+, D−. USB connector 10 contains a metal case that wraps around connector substrate 14. The metal case touches connector substrate 14 on three of the sides of connector substrate 14. The top side of connector substrate 14, holding metal contacts 16, has a large gap to the top of the metal case. On the top and bottom of this metal wrap are formed holes 12. USB connector 10 is a male connector, such as a type-A USB connector.
FIG. 1B shows a female USB connector. Female USB connector 20 can be an integral part of a host or PC, or can be connected by a cable. Another connector substrate 22 contains four metal contacts 24 that make electrical contact with the four metal contacts 16 of the male USB connector 10 of FIG. 1A. Connector substrate 22 is wrapped by a metal case, but small gaps are between the metal case and connector substrate 22 on the lower three sides. Locking is provided by metal springs 18 in the top and bottom of the metal case. When male USB connector 10 of FIG. 1A is flipped over and inserted into Female USB connector 20 of FIG. 1B, metal springs 18 lock into holes 12 of male USB connector 10. This allows the metal casings to be connected together and grounded. Universal-Serial-Bus (USB) is a widely used serial-interface standard for connecting external devices to a host such as a personal computer (PC). Another new standard is PCI Express, which is an extension of Peripheral Component Interconnect (PCI) bus widely used inside a PC for connecting plug-in expansion cards. An intent of PCI Express is to preserve and re-use PCI software. Unfortunately, USB connectors with their 4 metal contacts do not support the more complex PCI Express standard.
FIGS. 2A-2B show an ExpressCard and its connector. A new removable-card form-factor known as ExpressCard has been developed by the Personal-Computer Memory Card International Association (PCMCIA), PCI, and USB standards groups. ExpressCard 26 is about 75 mm long, 34 mm wide, and 5 mm thick and has ExpressCard connector 28.
FIG. 2B shows that ExpressCard connector 28 fits into connector or socket 30 on a host when ExpressCard 26 is inserted into an ExpressCard slot on the host. Since ExpressCard connector 28 and socket 30 are 26-pin connectors, they contain many more signals than a 4-pin USB connector. The additional PCI-Express interface can be supported as well as USB. ExpressCard 26 can also use USB to communicate with the host. Differential USB data signals USBD+ and USBD− are connected between ExpressCard 26 and a host chip set. The host chip set contains a USB host controller to facilitate communication with ExpressCard 26.
PCI Express supports data rates up to 2.5 G/b, much higher than USB. While the ExpressCard standard is useful for its higher possible data rate, the 26-pin connectors and wider card-like form factor limit the use of ExpressCards. The smaller USB connector and socket are more desirable than the larger ExpressCard. Another interface, serial AT-attachment (SATA) supports data rates of 1.5 Gb/s and 3.0 Gb/s. However, SATA uses two connectors, one 7-pin connector for signals and another 15-pin connector for power. Due to its clumsiness, SATA is more useful for internal storage expansion than for external peripherals. While SATA and ExpressCard are much higher-speed interfaces than USB, they use larger, bulky connectors while USB has a single, small connector.
FIGS. 3A-3D shows cross-sections of a prior-art USB connector and socket. In FIG. 3A, a prior-art peripheral-side plug or USB connector has plastic housing 36 that the user can grip when inserting the USB connector into a USB socket such as the socket in FIG. 3B. Pin substrate 34 can be made of ceramic, plastic, or other insulating material, and supports metal contact pins 32. There are 4 metal contact pins 32 arranged as shown in the top view of pin substrate 34 in FIG. 3D. Metal cover 33 is an open-ended rectangular tube that wraps around pin substrate 34 and the gap above metal contact pins 32. In FIG. 3B, a prior-art host-side USB socket is shown, such as a USB socket on a host PC. Metal cover 38 is rectangular tube that surrounds pin substrate 42 and has an opening to receive the USB connector's pin substrate 34. Metal contact pins 44 are mounted on the underside of pin substrate 42. Mounting pin 40 is formed from metal cover 38 and is useful for mounting the USB socket to a printed-circuit board (PCB) or chassis on the host PC.
Metal contact pins 44 are arranged as shown in the bottom view of pin substrate 42 of FIG. 3C. The four metal contact pins 44 are arranged to slide along and make contact with the four metal contact pins 32 when the USB connector is inserted into the USB socket. Pin substrates 34, 42 are formed in an L-shape with matching cutouts above metal contact pins 32 and below metal contact pins 44 that fit together when inserted. Metal contact pins 32, 44 can have a slight bend or kink in them (not shown) to improve mechanical and electrical contact. The bend produces a spring-like action that is compressed when the USB connector is inserted into the USB socket. The force of the compressed spring improves contact between metal contact pins 32, 44. While useful, prior-art USB sockets and connectors have only four metal contact pins 32 that mate with four metal contact pins 44. The four metal contact pins carry power, ground, and differential data lines D+, D−. There are no additional pins for extended signals required by other standard buses, such as PCI Express or Serial ATA.