Wired Interfaces: Paving the Way for ADAS and Automotive Connectivity

We talk with Rick Wietfeldt, MIPI Alliance board member and senior director at Qualcomm Incorporated, who will be presenting virtually at AutoSens Detroit on October 28th. Rick discusses how wired interfaces are helping to make advanced driver-assistance systems (ADAS) and eventually autonomous driving possible. He also discusses a new long-reach SerDes physical layer interface that MIPI has developed as part of an end-to-end automotive wired connectivity solution.

For those who are not familiar with the MIPI Alliance, can you summarize the aims of the organization and who is involved?

MIPI Alliance develops interface specifications for mobile and mobile-influenced industries. Since its founding in 2003, it has developed specifications that are used in every smartphone made today and can be found in all sorts of devices and markets, such as IoT, medical, industrial, avionics and automotive. MIPI specifications already have been in cars, for instance, for at least the last 10 years. All MIPI specifications are designed to fulfill four major attributes: high performance, low power consumption, low electromagnetic interference (EMI) and low conductor count.

MIPI has more than 325 member companies in the mobile industry and other fields, including handset makers, semiconductor companies and software providers. One of the fastest-growing segments of our membership are companies in the automotive sector. Forty-five percent of MIPI member organizations work on automotive electronic systems and ADAS applications.

Last year MIPI released a white paper called “MIPI Alliance: Driving the Wires of Automotive.” How do you see MIPI continuing to evolve in the field of autonomous/semi-autonomous driving?

 The automotive industry today is in many ways similar to the mobile industry in the early 2000s. The rapid growth of automation, in both driver assistance systems and early self-driving cars, has turned vehicles into increasingly complex systems that need fast, standardized data interfaces.

New cars are on the verge of shipping with up to 12 cameras, along with radar, lidar and other sensors to monitor their surroundings. As automation and onboard infotainment grow more sophisticated, vehicles also need more and better displays. Some vehicles now have four or more screens of different sizes and resolutions filling the dashboard. Both of these exciting areas of development, coupled with the underlying need for functional safety and security, significantly increase connectivity and bandwidth requirements. MIPI is advancing its wired interface specifications to meet the requirements of next-generation vehicles.

For example, MIPI Camera Serial Interface (MIPI CSI-2) and Display Serial Interface (MIPI DSI-2) are used throughout the auto industry to link cameras and displays to onboard ECU processors.

CSI-2, implemented with the MIPI C-PHY or D-PHY physical interfaces, has the capacity to support cameras with resolutions of more than 40 megapixels and video capture rates of more than 4K/120 frames per second or 8K/30fps, while DSI can provide more than two gigapixels per second of uncompressed image content. Its transport layer also incorporates the VESA Display Compression-M (VDC-M) and VESA Display Stream Compression (DSC) standards for up to six times compression of display payloads.

Both of these specifications will get an update within months, with additional service extensions to support functional safety and security to make them even better equipped for highly automated vehicles.

CSI-2 v4.0, for instance, will support advanced AI-powered visions applications such as drowsy-driver detection, while the Camera Service Extensions will include provisions to help it meet the needs of the Automotive Safety Integrity Level (ASIL-B and ASIL-D) specifications in the widely used ISO-26262 standard. Similarly, DSI-2 v2.0 will add display service extensions to support functional safety, security and HDCP for content protection.

These specifications will be supported with a new physical layer specification, MIPI A-PHY that can span an entire vehicle, linking components such as cameras and displays to ECUs. I look forward to sharing more details on this during my 28 October presentation, but I will provide a preview in the response below.

What can you tell us about the upcoming MIPI A-PHY specification?

MIPI A-PHY is a new serializer-deserializer (SerDes) physical layer interface for automotive applications. It offers OEMs and Tier 1 suppliers another way to reduce complexity while meeting demands for high performance. Most long-reach interconnects in today’s vehicles are proprietary, so manufacturers are forced to prepare components for use with several possible specifications. As a standardized interface, A-PHY removes the need for these proprietary links while offering flexibility for a variety of designs.

A-PHY is being developed as an asymmetric data link in a point-to-point topology, with high-speed unidirectional data, embedded bidirectional control data and optional power delivery, all over a single cable. It will run on coaxial cables up to 15 meters long or on shielded differential pair (SDP) cables, while offering ultra-high immunity to EMC effects and an ultra-low packet error rate (PER) of 10-19. Version 1.0 supports 5 speed gears (2, 4, 8, 12 and 16 Gbps), with a roadmap to 48 Gbps and beyond.

At first, A-PHY can be inserted between subsystems that internally use MIPI short-range protocols such as D-PHY and C-PHY. Bridge chips will still be needed to connect with long-range interfaces, but the makers of these chips will be able to reduce the number of protocols they have to support. Later, we expect vendors to implement A-PHY all the way from sensor modules to ECUs anywhere in the vehicle, eliminating bridges and further cutting costs. Because the protocols such as CSI-2 and DSI-2 are tightly hardware-coupled with A-PHY in both scenarios, the need for a separate software stack is eliminated. There will also be a generic link layer and adaptation layers that will enable multiple data streams on the same wire, as well as support the use of other MIPI-approved third-party protocols, such as VESA’s Embedded DisplayPort and DisplayPort standards.

Tell us about your updated sensor-to-processor bus specification. How could it benefit the automotive market?

MIPI I3C was introduced in 2018 as a general-purpose, low-speed control bus or messaging interface between sensors and processors, offering a way to simplify the integration of sensors. Last December, it was updated to MIPI I3C v1.1, gaining multilane capability and other improvements.

I3C was developed as a backward-compatible advancement over I²C and a replacement for SPI and UART interfaces. In automotive, it is used to link ECUs with a variety of sensors, including engine speed, pressure, temperature, and window and seat controls. For vehicle applications that require higher data rates, such as imaging, it can be used in conjunction with interfaces such as MIPI CSI-2 for control and management of the sensor.

An important addition with I3C v1.1 is HDR-BT mode, an improved transport capability that allows for the use of multiple lanes. This can increase the effective throughput of an I3C interface from about 25 Mbps to nearly 100 Mbps, allowing designers to double the speed by going from one to four data lanes. Version 1.1 also adds enhanced error detection and recovery, power management and other features.

What’s the biggest challenge MIPI aims to solve for its member companies in automotive beyond 2020? 

The new possibilities in vehicle automation come with challenges that designers and developers constantly face. Adding sensors, displays and onboard ECUs may increase weight, cost, complexity and energy use in vehicles that are already under tight constraints. The biggest challenge MIPI is tackling for automotive companies is how to keep improving automation while minimizing these challenges.

MIPI has been evolving and optimizing interface specifications for performance, space, weight, efficiency and simplicity since its inception. That strategy is as vital as ever in automotive: MIPI interfaces used in cars, such as CSI-2, DSI-2 and I3C, all offer high performance with low power, low conductor counts and low EMI. All these features help automotive developers pack the necessary performance into parts and vehicles that meet stringent requirements. MIPI A-PHY, as part of an end-to-end automotive wired connectivity solution, will extend those same qualities across the vehicle.

We’re looking forward to hearing from you at AutoSens in October. What are you looking forward to about being involved?

Representing MIPI Alliance at a major automotive tech conference is a great opportunity to spread the word about MIPI’s continued evolution to support automotive ecosystems. I also look forward to hearing firsthand about the latest research and technical implementations.

This is an exciting moment in the automotive industry. The innovations we introduce and bring to market have the potential to shape the driving experience and transportation ecosystem for years to come. It’s great to see OEMs, suppliers and standards organizations like MIPI Alliance collaborating to make that future possible.