Last October, Basler Vision Technologies (Exton, PA) and Pulnix America (Sunnyvale, CA) joined forces to promote a common digital-camera interface based on the Channel Link technology developed by National Semiconductor (Santa Clara, CA). Channel Link technology is derived from National's OpenLDI specification (seeVision Systems Design, Nov. 1999, p. 40).
In operation, OpenLDI uses a set of transmitters to serialize parallel pixel data and sends these data from the camera to the host. At the host, a set of receivers returns these data to a parallel format. According to Chris Seymour, Basler product-development manager, the collaboration between Pulnix and Basler will make the transition from the traditional RS-644 data-transfer protocol more attractive. Although RS-644 is a low-voltage differential-signal (LVDS) protocol similar to RS-422, it requires less power and allows longer cable lengths and higher clock rates than does RS-422.
"Basler is moving away from RS-644 to support cameras with higher data rates, such as its A210 50-frame/s device," says Seymour. "Channel Link provides a high-bandwidth link and low-cost cabling and reduces the complexity and cost of a system," he adds. Using a parallel interface in the design of Basler's A210 50-frame/s camera, for example, requires approximately 60 conductors to carry image data, power, ground, line-valid, and pixel-clock data. "Using Channel Link reduces the number of conductors to 26," declares Seymour.
At present, serial-link interfaces based on LVDS technology are available as Channel Link from National Semiconductor, PanelLink from Silicon Image (SI; Cupertino, CA), and FlatLink from Texas Instruments (Dallas, TX). "We are aware of Channel-Link-compatible products such as FlatLink and Panel Link," says Manish P. Shelat, Pulnix product-marketing manager. "But unlike the flat-panel-display industry, 'very-high' speed is not a big issue in the camera industry," he says.
Adopting such digital interfaces will certainly be the first step in allowing camera vendors to add intelligence into their devices. When this happens, the next generation of smart cameras may only need to update the host computer when new information needs to be transferred, thereby reducing bandwidth requirements even further.
