Enhancing Automotive Head-Up Display Systems with ROHM’s ML86178 Controller IC

Head-up displays (HUDs) allow drivers to maintain their focus on the road while still accessing important data such as speed, navigation instructions, and vehicle status by projecting information directly onto the windshield. As HUDs have become more advanced, they can even provide augmented reality (AR) features by superimposing virtual elements for a more immersive and intuitive driving experience.

However, integrating high-resolution HUDs can be challenging for automakers and Tier-1 suppliers, with key challenges including interfacing various video sources and displays, as well as the need to correct the projected images to ensure they are easily visible to drivers on the windshield. Parallel interfaces, including LVDS and LVTTL, as well as newer interfaces like MIPI DSI make compatibility and integration between systems more complex. Additionally, image correction tasks such as distortion correction increase the processing load on the system, further complicating the implementation of HUDs.

Automotive HUD Systems: Trends and Challenges

Full HD (1920 x 1080) and higher resolutions have become more common in automobiles, due to the need for more detailed visual information within vehicles. High-resolution displays are not just enhancing the clarity of HUD elements (e.g., speed and navigation), but also providing AR features and improved graphics. For example, AR-HUDs can overlay virtual objects, identifying potential hazards, points of interest, and traffic information in real-time. There is also a trend in integrating landscape-oriented displays in HUD systems since such displays offer a wide field of view for expansive and immersive AR experiences.

However, introducing higher-resolution and/or landscape displays creates challenges with video interfacing. The main reason for this is that automotive systems utilize a mix of display interface standards, each with its own benefits and limitations. For example, parallel interfaces like LVDS and LVTTL have been favored for their simplicity and robustness, but struggle to accommodate the higher bandwidths required by high-resolution displays. On the other hand, new interfaces, such as MIPI DSI offer higher data rates and design flexibility, but require careful signal integrity management and protocol compliance.

As highlighted previously, HUDs also require powerful video processing capabilities to maintain legibility and accuracy of projected information. High frame rates and low latency are critical for smoother and more responsive visual feedback, e.g., in AR applications where virtual content must align precisely with real-world elements. Similarly, geometrical transformations, such as warping, are essential to compensate for the curvature of the windshield and correct any optical distortions introduced by the HUD’s optics. These transformations usually involve complex math operations and require powerful image processing hardware to maintain visual performance.

Lastly, HUDs and associated components must also withstand harsh operating conditions and meet the reliability requirements of automotive environments–extreme temperatures, vibration, and noise can impair the performance and longevity of components over the life of the vehicle. Functional safety considerations, like ISO 26262, also mandate extensive design and validation to ensure the reliability of safety-critical systems, like HUDs. Consequently, manufacturers must select and integrate HUD components that can withstand such challenging conditions and meet the industry safety standards.

ROHM’s Automotive-Grade ML86178 HUD Controller

ROHM’s ML86178 is a purpose-built controller IC that is suited to address the challenges of automotive HUDs by offering flexible video input and output interfaces, advanced processing capabilities, and automotive-grade reliability.

One benefit of the ML86178 HUD controller is its versatility in video interfacing, supporting both single and dual LVDS inputs at resolutions up to full HD. This enables smooth integration with a broad range of automotive SoCs and image sources that utilize LVDS interfaces. For legacy systems relying on parallel interfaces, the ML86178 can accept LVTTL input up to 1280 x 720 resolution, ensuring backward compatibility and smooth transitioning.

Block diagram of the ML86178 HUD controller

On the output side, the ML86178 IC offers single and dual LVDS outputs, supporting resolutions up to 1920 x 1080. This allows designers to establish direct connection to high-resolution HUD display panels, eliminating the need for additional interface conversion stages. Moreover, the IC offers a MIPI DSI output option for integration with newer display technologies that leverage this high-speed interface. Overall, the ML86178’s flexibility in output interfaces simplifies HUD system architecture and reduces the component count.

The ML86178 IC offers advanced image processing with a multi-region warping engine that can independently configure up to four distinct areas of the display. This allows precise geometrical transformations to be applied to specific regions for more accurate projection and alignment of HUD content. This warping engine supports high-precision coordinate transformation with a grid resolution ranging from 5×5 to 32×32 to minimize image distortion. This IC also incorporates an image processing pipeline that provides scaling, rotation, color space conversion, and gamma correction. The scaling and rotation engine achieves smooth and high-quality resizing of video content to match the resolution/aspect ratio of HUD displays, while color space conversion and gamma correction features enhance visual performance, color accuracy and contrast.

HUD content distortion correction with the ML86178 HUD controller

To further enhance the HUD user experience, ROHM’s ML86178 IC offers an on-screen display (OSD) functionality to overlay up to 10 OSD windows with 2 layers, enabling flexible placement of telltales, icons, and other textual information on top of the main video content. OSD windows can be configured as 16-color or 256-color bitmaps, with support for transparency effects.

To meet the strict safety requirements of automotive systems, ROHM designed its ML86178 IC with a range of safety features. It continuously monitors input and output signals for anomalies, including frozen frames or signal loss, and also detects brightness abnormalities and occlusions in the display area. When an error condition is detected, it triggers error reporting and fail-safe mechanisms to ensure a safe and controlled system response.

Occlusion detection with the ML86178 HUD controller

The ML86178 is housed in a 128-pin TQFP package, making it suitable for space-constrained electronic control units (ECUs). This IC prioritizes low power consumption and optimal thermal performance, contributing to overall efficiency and reliability of HUD systems. ROHM plans to achieve AEC-Q100 qualification for the IC via rigorous testing to withstand extreme temperature ranges, electrostatic discharge, and other environmental stresses.

How ROHM’s ML86178 Addresses HUD System Challenges

To address HUD system challenges, ROHM has developed a highly integrated controller IC designed for automotive applications. This solution supports a wide range of video input and output interfaces, making it compatible with various automotive ecosystems. It offers advanced image processing capabilities, such as multi-region warping and distortion correction for precise alignment and clarity of HUD content.

By integrating multiple functions into one single chip, the ML86178 simplifies the overall system architecture and reduces the number of external components. This integration not only saves valuable board space but minimizes bill of materials cost. For automakers and Tier-1 suppliers, the ML86178 can provide a scalable and future-proof platform for HUD development. Its flexible architecture accommodates a wide range of resolutions and aspect ratios, allowing designers to choose the best display configuration for their application.

Key Applications

The ML86178 HUD controller features and high level of integration make it suitable for use in a broad range of applications. Automakers can benefit from the ML86178’s configurable features and high performance to create entry-level HUD solutions for mass-market vehicles or high-end systems for both premium and luxury segments.

By identifying potential hazards like pedestrians walking across the road or vehicles in a driver’s blind spot, Augmented Reality HUDs (AR-HUDs) enhance situational awareness and minimize distraction. These systems can use the ML86178’s warping and image processing capabilities to overlay navigation guidance, speed limits, and other important driver assistance information.

Another key application for the ML86178 is in instrument cluster displays with integrated HUD functionality. By augmenting standard instrument cluster information with HUD-style projections, automakers can create a more immersive and informative driving environment. The ML86178’s OSD feature can be used to customize the display layout, prioritizing critical information based on road/driving conditions. For example, a HUD can display speed and navigation data while on the highways, or battery status and range information in EVs.

The ML86178 can also be applied in driver monitoring systems (DMS) that utilize cameras and sensors to track a driver’s attention level, gaze direction, and head position. By displaying DMS information on a HUD, the ML86178 IC can provide visual feedback and safety alerts to drivers. For instance, when the system detects signs of drowsiness or distraction, it can send a warning message or suggest taking a break.

Conclusion

HUDs are essential for maintaining vehicle safety while enhancing the overall user experience. Challenges for automakers designing HUD systems include interfacing multiple video sources, performing complex image processing tasks and reliable operation in automotive environments. ROHM’s ML86178 HUD Controller addresses these limitations with its flexible video input and output architecture, support for multiple interfaces, and automotive-grade robustness, providing a foundation for designing high-performance HUD systems.

To discuss specific HUD system requirements and explore how the ML86178 can benefit your designs, please contact your local ROHM sales rep or visit the website for more information.