DISPLAYS & UIs


Bridge ICs: A translator for images and videos on any device


Zibo Su, product manager digital at Rutronik discusses how bridge ICs are advancing the user interface in next generation devices


in smartwatches and in automobiles. Users expect crystal-clear playback with zero judder – on any medium. Bridge ICs are used to make this possible, even with different standards. The most well known differential method for


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fast transfers of large amounts of data at rates of up to several Gbit/s – and thus for image and video content – is LVDS (low- voltage differential signaling technology). Developed by National Semiconductor, LVDS was standardised as EIA-644 by the EIA (Electronic Industries Association). It is a free and open standard that is used by many IC suppliers. LVDS is a unidirectional connection that


works very energy-efficiently. This technology uses the voltage differential between two copper cables to transfer information. The LVDS transmitter encodes up to 24-bit data based on an input clock over four serial differential pairs (see Figure 1). A terminating resistor prevents reflection back to the signal source. Because LVDS works with low voltages of


under 3.3V, the technology requires little current and generates only minor


isplays are being found in more and more devices – even in the refrigerator,


electromagnetic interference. Common- mode voltages generating an electromagnetic wave are eliminated by the differential. LVDS only describes the physical level;


several other communication standards are based on it, including FPD-Link (Flat Panel Display), FPD-Link II & III, MIPI (Mobile Industry Processor Interface) and DVP (Digital Video Port).


LVDS with FPD-Link When we talk about LVDS, we usually mean the FPD structure. FPD-Link was developed alongside LVDS by National Instruments and remains the standard today for the transmission of graphical and video data between notebooks, tablet PCs or LCD televisions and their display. FPD-Link chipsets consist of transmitters


(TTL to LVDS) and receivers (LVDS to TTL) that support 18 and 24-bit colour displays. At the TTL level, the RGB data and control data from the graphics controller is transmitted to the inputs of the FPD-Link transmitter. It acts as a multiplexer (mux) for the parallel TTL data and converts it to the serial LVDS standard. The LVDS data is sent to the outputs of the transmitter via the cable


connecting the mainboard to the display. At the FPD-Link receiver on the display, they are deserialized (demuxed), which means that they are converted back into TTL signals and sent to the inputs of the timing controller. Multiplexing the parallel TTL signals allows higher-speed data to be transmitted over a narrow-band interface. Even so, the requirements of high-bandwidth communications are met. Figure 2 shows the structure of an FPD-Link


with four LVDS wire pairs. Three of the four cables transmit the graphics and video signal, while the fourth conveys the LVDS clock signal. The mux circuit serialises the parallel graphics and video signal and transmits it over the differential pair. Thus, only three cables are needed as opposed to the 22 otherwise needed, and there is also an improvement in electromagnetic compatibility. FPD-Link chipsets are available with falling


and rising edges and programmable data import to provide a convenient interface with a variety of graphics and LCD panel controllers. The 5V or 3.3V chipsets support a frequency range of 20 to 65MHz.


Figure 1: An Embedded Clock Serializer with a Single LVDS Channel 28 OCTOBER 2021 | ELECTRONICS TODAY


MIPI The MIPI Alliance has specified six types of interfaces in mobile, networked devices: for the physical level, multimedia, chip-to-chip or interprocess communication, device control and data management, system debugging and software integration. Each specification satisfies the most important requirements of these devices: low energy consumption, high bandwidth and low electromagnetic interference. DSI (Display Serial Interface) and DSI-2 are the MIPI interfaces between one or several


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