Since MIPI and MDDI standards both target interfaces to cameras and displays on mobile devices, are two separate standards really needed?
By Ashraf Takla, Mixel and Timothy Saxe, QuickLogic
The accelerating use of smartphones and the emergence of an exciting class of mobile Internet devices (MIDs) and Netbooks are creating an explosion of data transfer across wireless networks. Such full-featured devices give the consumer a multimedia viewing and listening experience, higher-resolution photography, and a richer set of applications like Web browsing and Global Positioning System (GPS) navigation. Cell-phone manufacturers and the chip providers that supply them need to decide which interface bus to use to support the required low-power, high-speed data transfer between the components that make up these new devices. The Video Electronics Standards Association’s (VESA’s) Mobile Display Digital Interface (MDDI) and the Mobile Industry Processor Interface Alliance’s (MIPI’s) display and camera interfaces provide overlapping standards to meet these requirements. Each standard is a reflection of its origin and the industry participants driving it. This article will explore the different aspects of MDDI and MIPI to help designers determine whether they need to support both of them in their next chip or system design.
Figure 1: Here is an example of a serial versus parallel display interface. Fewer serial wires simplify routing.
Parallel interfaces are less attractive for mobile devices now because of pin count, electromagnetic-interference (EMI) radiation, signal-integrity concerns at higher bus speeds, and higher power-consumption profiles. Large parallel-bus harnesses aren’t suited for connecting across hinged products like slider, swivel, or clamshell-type devices (see Figure 1). In addition, parallel buses add complexity to routing on the small printed-circuit-board (PCB) footprints in mobile devices.
The need for serial interfaces began with the need to address the shortcomings of legacy parallel-bus connections. To solve these issues, companies jumped in to provide proprietary interfaces. For example, Texas Instruments introduced the FlatLink3G serializers and deserializers to provide a high-speed interface between liquid-crystal-displays (LCDs) and mobile application processors, such as its OMAP platform. These sub-low-voltage-differential-signaling (sub-LVDS) serializers work for red/green/blue (RGB) color data. They support screen resolutions from QVGA through XGA including VGA. QUALCOMM entered the fray as well with MDDI. A key aspect of these interfaces was that the transmitter side could be integrated into the baseband application processor and the receiver side in the display. A number of other companies also introduced proprietary solutions, bringing more choice and confusion.
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