Fostering an ecosystem of interface specifications for connected devices
Our smartphones have become indispensable and the value we attach to these devices will continue to grow along with steadily advancing device capabilities. New designs coming to market showcase increasingly sophisticated components: ever-faster 4G/LTE and Wi-Fi modems, higher resolution cameras, 4K ultra-HD displays, high-definition audio, and a plethora of sensors enabling mobile health, smart home, and other compelling applications.
The components share a common feature: they are integrated into a device as peripherals that interface to the application processor. The interfaces themselves, designed and crafted as carefully as the parts they interconnect, are provided in large part by the MIPI® Alliance, an international organization that specializes in this intricate work.
MIPI Alliance exists to develop interface specifications that enable components to interconnect and interoperate within the complex, demanding mobile device operating environment. The organization addresses interface needs for the entire mobile device, including the modems, antenna, various other peripherals, and application processor. It is the only organization focusing on these needs.
Formed in 2003, MIPI Alliance has released more than 45 interface specifications, bringing interoperability to device components to yield design and cost efficiencies that standardization provides. Most smartphones on the market today employ many MIPI Alliance interfaces.
MIPI Alliance is independent but works closely with other groups to enable other industries to use its specifications. As mobile connectivity increasingly finds its way into other markets, from PC to automobile products and to the burgeoning Internet of Things (IoT), MIPI specifications are gaining additional influence and helping drive growth in these ecosystems. In the PC industry, for example, the JEDEC Solid State Technology Association, USB Implementers Forum, and PCI SIG® have all leveraged MIPI technologies to deploy their protocols in mobile devices.
State-of-the-art interfaces meet emerging market needs
MIPI Alliance’s new sensor specification, MIPI I3C℠, addresses the needs of sensors in smartphones by advancing traditional I2C and SPI interfaces for use in the mobile context. Designers can use the interface to streamline and scale sensor integration for all types of mobile products and help drive the IoT.
Evolving technology is yielding higher resolution cameras and displays and MIPI Alliance specifications are helping facilitate these exciting features for end users. The MIPI Display Serial Interface (DSI℠), for example, can support 4K resolution to enable brilliant, realistic color rendering for the most demanding high-definition imagery.
Global roaming on 4G/LTE devices is a fundamental need that the organization is helping address with its MIPI RF Front-End interface (MIPI RFFE℠). This interface, pervasive in the market, offers a common method for controlling power amplifiers, antennas, and other front-end devices. The latest release, the MIPI RFFE v2.0 specification, improves interface characteristics for smartphones that use complex, multiradio systems and will help 3G/4G-based products operate in multiple frequency bands.
A holistic and comprehensive interface framework
MIPI Alliance interfaces are offered within a framework of specifications that serve four device interface categories: multimedia, chip-to-chip, control/data, and debug (see Figure 1). MIPI specifications offered across these categories enable engineers to interconnect a complete inventory of mobile device components (see Figure 2).
Multimedia interfaces are the most popular; these support cameras, displays, audio codecs, microphones, speakers, and storage as well as FM radio, NFC, Bluetooth and GPS.
Chip-to-chip interfaces are also widely used. These high-speed interfaces provide interprocess communications (IPC) between a 4G/LTE or Wi-Fi modem and the application processor.
Control/data interfaces are used for lower-speed components including batteries, sensors, and RFFE devices.
Debug/trace interfaces are used for debugging increasingly complex embedded systems at gigabit speeds. For example, MIPI specifications can facilitate debugging via USB 3.0 and can be used to debug devices already in the field.
Interface options serve component and architectural needs
MIPI Alliance makes its specifications available as individual interfaces. Companies can adopt whichever ones they prefer to differentiate their designs or support particular technology requirements or architectures.
For example, MIPI Alliance offers three physical layer (PHY) interfaces (MIPI C-PHY℠, MIPI D-PHY℠, and MIPI M-PHY™) to support a variety of device protocols and configurations. A classic smartphone could use MIPI D-PHY for camera and display applications, for example, while a manufacturer may choose MIPI C-PHY because it lowers the interface signaling rate relative to MIPI D-PHY. Google has adopted MIPI M-PHY, combined with the MIPI UniPro℠ transport layer in the MIPI UniPort-M interface, to serve the modular needs of its Project Ara smartphone platform. MIPI M-PHY also enables PC protocols, mentioned earlier, to operate in mobile terminals.
3 fundamentals: High performance, low power, low EMI
MIPI Alliance specifications address the mobile industry’s very special needs for high performance, low power, and low electromagnetic interference (EMI) interfaces.
High performance interfaces are needed to support a full range of performance demands in a device. These include the high data throughput that 4K displays and high-resolution cameras require and the high data speeds that 4G/LTE and 802.11ac Wi-Fi technologies must deliver.
Low-power operation is always required. MIPI Alliance interfaces use low-power signaling in both active and idle states. This minimizes interface power consumption and helps preserve battery life, enabling users to enjoy extended hours of feature-rich operation.
Low EMI helps minimize interference created by the many interfaces on the many radios present in a device. MIPI specifications deliver low EMI by employing slew rate control and low voltage swings. The techniques enable multiple radios to coexist in devices and also prevent interference from impacting displays and other features.
Looking to the future
MIPI Alliance has a heritage of providing device interfaces the mobile industry needs and will continue this support as technologies continue to evolve. While anticipating new smartphone trends, it is also focused on the broader device market. Today’s ultra-low-tier mobile devices are likely to take on more sophisticated capabilities in the coming years and MIPI Alliance will support this evolution.
As increasingly more devices in the “mobile influenced” sphere incorporate smartphone capabilities, components in these devices will need the attributes MIPI Alliance specifications can facilitate. Alliance interfaces are already used for multimedia display and camera applications in cars, for example. The organization also expects its technologies will have important roles to play in wearables, augmented reality, healthcare and the IoT.