High-definition displays hit the highway

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National Semiconductor's FPD-Link II chipset has features that control EMI in infotainment modules and interconnects.

More and more high-definition (HD) video content is becoming available through in-vehicle media players, TV tuners, and telematics links while navigation and visual-based driver-safety features proliferate. To benefit from these infotainment trends, automotive manufacturers are designing multiple high-resolution flat-panel displays (FPDs) into their luxury models and planning for dual-view capability in the central console. The new FPDs are meant to inform drivers and foster greater safety, while entertaining passengers with the latest high-quality videos and Internet browsing.

The visually more-pleasing monitors are intended to drive new car sales and profit margin, first in luxury models, followed by high- to mid-range vehicles once manufacturers deploy FPDs more widely. This drives system architects and designers to develop modular infotainment systems that scale across models and interconnect to transport multimedia data between modules. However, they must first overcome many hurdles.

The challenges to delivering high-resolution multimedia data streams through the automotive environment are daunting. Not only must the architects and designers conquer tough electromagnetic compatibility requirements regarding emissions, immunity, and transients, but they must also use interconnects that accommodate the mechanically structured passenger compartments.

For rear-seat entertainment monitors, cable lengths can easily exceed 7 m (23 ft), which requires advanced signal conditioning for data integrity. In addition, the solution must scale from luxury to mid-range vehicles as well as to higher resolution and deeper color displays that will start appearing in luxury models soon.

FPD types going into automotive applications are typically 6 in and larger, with many not of standard video sizes. For example, a 1280 x 480 FPD having an unconventional “dual VGA” resolution can serve as a central information display. The data rates required to drive FPDs depend on the resolution and blanking period, frame rate, and color depth.

To determine the necessary pixel clock to drive the desired resolution, a designer multiplies the total horizontal pixels (including blanking) by the total vertical lines (including blanking) by the frame rate. Assuming the rate is 60 frames per second, the pixel clock on a 1280 x 720 display is 73 MHz. The total data rate then depends on the color depth, which for current automotive displays is typically 18 bits per pixel (bpp)—6 bits each for red, green, and blue.

To video-up this display, the interconnect needs to deliver over 1.3 Gigabits per second (Gbps) for an HD visual experience. The data rate for automotive FPDs can range from a hundred Megabits per second (Mbps) to nearly 3 Gbps.

Transferring this wide range of data between head units and display modules requires cables and connecters that carry multi-Gbps data and are economical, lightweight, and flexible. The solution is a single differential pair for the multimedia data stream that is rugged enough for automotive applications. Therefore, using serialized data streams that scale from a few hundred Mbps to multi-Gbps are the best solution for infotainment displays.

Other challenges are protecting the serial data stream against electromagnetic interference (EMI) and preventing the data stream from interfering with its surroundings.

Features in National Semiconductor’s FPD-Link II chipset mitigate the EMI concerns. The Serializer takes in spread-spectrum data and clock and then uses it to spread the noise spectrum of the serial data streamed over the cable. In addition, the Serializer uses reduced differential voltage levels and a de-emphasis feature that reduces the signal level but maintains the signal integrity. Furthermore, the integrated terminations with accessible center tap point minimize the noise on the serial link. The designer uses the center tap access to build a common-mode filter via a capacitive connection to ground.

The interconnect solution carries these EMI control features all the way through to the display module. The FPD-Link II Deserializer uses an integrated spread spectrum clock generator (SSCG) and very low drive strength to minimize the interference generated by these signals inside the display module.

The automotive display future continues to improve as evidenced by HD touch screens, dual view, and deeper color. New high-resolution capacitive touch panels are optimal for infotainment control, but ideally, they communicate back to the head unit over the same cable carrying the multimedia data. Dual-view display panels, which enable two separate displays on a single panel, allow the driver to see safety information through one view perspective while the second view entertains the passenger.

As these visual advancements continue to scale-up the streaming data rate, National’s FPD-Link II and next-generation video transport solutions will continue to supply infotainment architects and designers with the tools necessary to meet their customer’s demands.

Stephen Kempainen, Strategic Marketing Director, National Semiconductor Corp., wrote this article for Automotive Engineering.

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