Enhancing Automotive Display Systems with ROHM’s ML86797 Interface Bridge IC

Abstract

Leading automakers always seek to differentiate their products by designing connected, intelligent, and more visually appealing vehicles. For example, including sophisticated display interfaces improves the user experience and drivability. However, as automobiles integrate more high-resolution displays, designers must establish compatibility between multiple interfaces. This paper addresses the challenge of automotive display interfacing and introduces ROHM’s ML86797 Interface Bridge IC for flexible, high-performance video interface conversion. 

Automotive Display System Trends and Challenges

LVDS, MIPI DSI, and MIPI CSI are some of the most common interfaces used in automotive systems. LVDS offers a high-speed, low-power interface for automobile displays that transmits serialized video over a differential pair of wires with support for a wide range of resolutions and color depths. On the other hand, MIPI DSI and MIPI CSI were developed specifically for mobile and embedded systems, which include automotive systems. MIPI DSI is typically used for connecting displays to host processors, while MIPI CSI is used for connecting cameras to host processors. The coexistence of multiple interfaces adds complexity to the system design because designers must establish compatibility and integration between them. Moreover, automotive displays are getting higher resolutions in instrument clusters and infotainment, and these high-resolution displays require advanced processing, data transmission, and integration. 

Mismatches Between SoC, Camera, and Display Interfaces

A major pain point in automotive display system design is the mismatch among the interface formats of system-on-chip (SoC) processors, camera modules, and display panels. In many cases, the native interface of an SoC or camera module does not align with the interface requirements of the target display. For example, an SoC may have a MIPI DSI output, while the display panel uses an LVDS input. Similarly, a camera module may provide a MIPI CSI output, which must be converted to match the input interface of the SoC or display. Because the interface mismatches prevent proper connectivity and data flow between components, a failure to address them can lead to compatibility issues or performance degradation.

SoC manufacturers typically implement interfaces based on their specific requirements and target applications. For example, display panel manufacturers may select an interface optimized for a specific panel technology and resolution. Conversely, camera module producers may choose interfaces that suit sensor characteristics and data output formats. This lack of a universal interface standard across all components leads to the need for interface conversion and bridging solutions.

Resolving interface mismatches often involves changing  SoC or display. However, these approaches mainly increase developing time and cost. A far more efficient and streamlined solution is incorporating a dedicated interface bridge IC to handle the conversion and bridging of various interfaces in a single chip. These ICs provide a centralized and optimized approach to conversion, reducing the system complexity while ensuring high-quality video transmission.

Video Processing Considerations

MIPI-CSI and MIPI-DSI interfaces in automotive applications operate at speeds between  1Gbps and 2.5Gbps per lane. While this high-bandwidth transmission enables the delivery of detailed and smoother visuals, they require advanced video processing solutions capable of handling high frequencies. The challenge is that higher input frequencies affect signal integrity, timing accuracy, and power consumption because as data rates increase, signals become more susceptible to noise, jitter, and other impairments. Video processing at higher frequencies requires data handling and synchronization capabilities for video data feeds to be received, deserialized, and processed in real-time to avoid visual artifacts or latency. 

Another trend among leading automakers is using advanced color formats and higher bit depths to enhance the visual experience – newer displays are now providing deep color support and HDR capabilities. However, to accommodate the advanced color formats and higher bit depths, video processing solutions must have the necessary color depth-handling capabilities (e.g., support for various color spaces, such as RGB or YCbCr, color gamut mapping, and tone-mapping algorithms). This implies that the video-processing pipeline must be able to preserve color information throughout the entire signal path, from input to display. 

Automotive Environmental Requirements

Vehicles are subjected to a broad range of operating conditions, from extreme temperatures to vibrations and mechanical shock. In fact, operating temperatures for automotive electronics can range from –40°C to 105°C. These extreme temperatures degrade the electrical characteristics of automotive electronics, causing signal propagation delays, impedance, and noise margins. Moreover, exposure to high temperatures can lead to more leakage currents, reduced signal integrity, and accelerated component aging. Thus, electronics like display interfaces must withstand harsh environments and maintain reliable operation during the vehicle’s lifetime. 

Vibration and shock resistance are also important considerations in automotive display systems, because automobiles are subject to constant vibrations from road conditions, engine operation, and other mechanical sources. Display interface components must be mechanically robust and able to withstand vibrations without experiencing signal degradation or physical damage. Automotive displays must also be designed with thermal management in mind, given the compact nature of automotive electronics and limited space for heat dissipation. 

ML86797 Interface Bridge IC for Automotive Applications

The ML86797 Interface Bridge IC from ROHM addresses many of the complex requirements of automotive display systems. This product offers several features and specifications for interface conversion and supports high-resolution displays in demanding automotive environments.

A key advantage of the ML86797 is its flexible video input support – this IC accepts video signals from a range of interfaces, including MIPI-DSI, MIPI-CSI, and LVDS. This flexibility lets designers interface with various SoCs and camera modules regardless of their native output interfaces. By supporting multiple input standards, the ML86797 simplifies system integration and reduces the need for additional conversion components. The ML86797 IC supports MIPI-DSI input with as many as four lanes at speeds up to 2.5Gbps. This higher bandwidth allows high-resolution video (up to 4K and 6K) to be transmitted from the host to the processor to displays. 

For camera connectivity, the ML86797 offers MIPI-CSI input support with up to four lanes capable of operating at speeds up to 2.5Gbps. This allows direct connection of high-resolution cameras to the IC, eliminating the need for external conversion circuitry. 

Video Interface Conversion

The ML86797 supports both single and dual LVDS output configurations for compatibility with multiple display panels. This configurability allows designers the freedom to choose the most suitable display for their specific application, whether it’s a high-resolution instrument cluster, an infotainment system

The ML86797 is designed to handle video-processing requirements with support for resolutions up to 6K for ultrahigh-definition visuals. The IC uses a high-performance video processing engine to handle large amounts of video data, and a video-processing pipeline uses scaling, color space conversion, and frame rate conversion techniques to optimize video quality and to ensure smooth playback. ROHM’s ML86797 also supports a range of color formats, including RGB888, RGB666.

Compact Package and Low Power Consumption

The ML86797 is built with robust and reliable components to meet the stringent automotive environmental requirements. It is qualified to operate across a broad temperature range, from –40°C to +85°C, ensuring stable performance in extreme conditions. The ML86797 IC’s compact 64-pin 0.5 pitch WQFN package (very thin) is designed with advanced thermal management techniques, such as “exposed pad” and optimized pin assignment, to improve heat dissipation and minimize thermal resistance in space-constrained automotive ECUs and display modules.

Addressing Display System Challenges with ROHM’s ML86797 IC

The primary functionality of the ML86797 is converting between MIPI DSI, MIPI CSI, and LVDS, allowing designers to integrate components with various native interfaces into a single cohesive display system. This IC achieves video interface conversion through hardware. On the hardware side, it uses dedicated conversion circuitry for each supported interface that is responsible for the signal conditioning, synchronization, and protocol adaptation. For example, when converting MIPI DSI or MIPI CSI to LVDS, the ML86797 will first deserialize the incoming MIPI stream and extract the video payload. It then reformats the video data into LVDS, and a LVDS transmitter serializes the video data and transmits it over the LVDS interface to the display panel. 

The ML86797’s capability for handling multiple input and output interfaces provides flexibility in system design. Designers can choose the most suitable interface for each component based on bandwidth requirements, power consumption, and signal integrity. For instance, LVDS can be used for longer cable runs or in EMI-sensitive environments, while MIPI interfaces are better applied in high-bandwidth and low-power applications. The ML86797’s IC also provides a range of configuration options, such as lane count, data rate, and protocol settings, to establish compatibility among SoCs, cameras, and displays. This programmability “future-proofs” the IC, allowing it to accommodate newer interface developments and system requirements.

Key Applications

Image credit: ROHM

The ML86797 Interface Bridge IC can be incorporated into various automotive display applications. Below are a few examples that showcase the IC’s capabilities:

High-resolution instrument clusters

Instrument clusters offer drivers with a wealth of information, from vehicle speed and navigation directions to advanced driver assistance features. However, the interface between the SoC and the display panel is often mismatched. The ML86797 IC bridges this gap by converting between the SoC’s output (e.g., MIPI DSI) and the display panel’s input (e.g., LVDS). The ML86797’s high bandwidth ensures smoothness, even at the higher frame rates typical of instrument clusters.

Infotainment systems

Infotainment systems that provide navigation, multimedia playback, connectivity and more will typically include high-resolution displays to provide an immersive and interactive user experience. However, the integration of multiple video formats can be a challenge for system designers. The ML86797 supports multiple video interfaces, such as LVDS, MIPI DSI, and MIPI CSI, enabling conversion between sources, such as cameras, multimedia playback devices, and navigation systems.

The ML86797 serves as the central video hub in an infotainment system, handling the interface conversion and video switching. The IC can accept input from the rear-view camera, multimedia module, and navigation system and convert these video streams to the format required by the display panel with low latency. 

Conclusion

As centralized interface conversion solutions, bridge interface ICs help to streamline the design process and reduce the effort required for system integration. This allows designers to focus on developing core functionalities of their automotive display systems rather than deal with the complexities of interface mismatches. With support for multiple input and output interfaces like MIPI-DSI, MIPI-CSI, and LVDS, ROHM’s ML86797 Interface Bridge IC allows designers to mix and match various components with native interfaces. This flexibility can accelerate the development process, minimize system complexity, and improve overall system reliability. 

For more information on ROHM’s ML86797 Interface Bridge IC or to discuss your automotive display system requirements, please contact ROHM or visit our website at www.rohm.com.