Products and Services

A case study : The ultimate in monochrome displays

When BMW, the German automobile manufacturer, asked Philips/VDO Car Systems to design a cost-effective, line-fit navigation system complete with on-board LCD monitor for their new Series 3 cars, Philips began looking for a manufacturer capable of developing and producing a large passive, monchrome graphics display meeting the stringent requirements of the prestigeous car maker.

The module was to have a resolution of 64 x 120 pixels with a backlight in the characteristically bright orange BMW color. A luminance of better than 80 candelas/mē was required with an optical contrast greater than 10 at all viewing angles and at all temperatures within the operating range. Moreover, at temperatures below freezing, where LCD's have slow reponse times, no waiting for warm-up could be allowed. Indeed, full operation over a temperature range of -20° to 70° C was necessary along with resistance to static electric discharge, electromagnetic interference, vibration and shocks. Implicit in all this also was the requirement for an overall defect rate in the parts per million range.

To meet the challenge for this highly visible component, Philips turned to CFG and its state-of-the-art display technology. A DSTN liquid crystal glass was chosen for its inherently higher contrast. Drivers were then chosen to match the liquid crystal for optimum contrast at the multiplex rate desired. To keep dimensions at a minimum, the driver chips were mounted chip-on-board, using CFG's wire bonding know-how, along with a temperature compensation circuit designed to automatically correct for contrast changes due to temperature variation. To provide backlighting, 48 high-output, light-emitting diodes encased in a specially designed light guide box were used. Finally, to solve the problem of slow response at low temperatures, an optically transparent wirefoil was included for quick heating of the LCD.

The resulting module can be seen in BMW's new Series 3 cars equipped with Philips navigation systems: an extremely bright, visible liquid crystal display with a performance and quality unmatched by any monochrome LCD on the market.