FPD-Link III Serializers & Deserializers

Editor's Notes

• #2 Welcome to the training module on FPD-Link III Serializers & Deserializers.
• #3 This training module provides an overview of the FPD-Link III series of products by reviewing application challenges, explaining National’s approach to solving these challenges through continuous backchannel technology, and comparing it to other solutions.
• #4 FPD-Link III represents the third generation of National’s Flat Panel Display technology. The first FPD-Link devices were designed to meet the challenges of connecting displays to graphics processors in laptops by introducing reduced cabling using differential pairs. This technology is still used today in many display applications. National’s first automotive-specific video transport components were introduced in the FPD-Link III family of chipsets. These devices reduced wiring to a single differential pair to allow for the greater distance needed in automobiles and included improvements to reduce the amount of EMI emissions, simplifying automotive module design. These parts are also widely used in infotainment and driver assistance systems at major OEMs worldwide.
• #5 The FPD-Link Serializer & Deserializer chipsets are used to provide data links between video sources and video sinks. One big advantage of the chipsets is their ability to transfer uncompressed video data at very high data rates without the need of an additional controller overhead. Typical application examples include interfaces to LCD displays from head units, instrument cluster and heads-up display control boxes for driver information and passenger entertainment purposes. For rear seat entertainment displays, the display resolutions for future infotainment generations are going past high-definition standards like 720p. Therefore, the data throughput is increasing beyond 3 Gbps. On the driver assistance side, there is a strong trend to digital video interfaces from camera image sensors, which is different from the current National Television System Committee analog solutions. This development is driven by the increasing resolutions of CMOS imagers, going from VGA to megapixel. With the higher quality of pictures being captured, the forward-looking camera systems can fulfill multiple tasks with just one image sensor, like intelligent headlight dimming, collision avoidance/mitigation, traffic sign recognition or lane departure warning. For multi-camera systems providing park-assistance functions, the higher number of pixels available facilitates a seamless combination and “image stitching” of image frames from different sensors to provide panoramic or 360 degree, bird view, perspectives.
• #6 The FDP-Link III solutions are great for automotive applications, specifically multi-camera systems and infotainment displays. The DS90UB901/02 is targeted toward the camera input and driver assist system, as seen on the left. Some of the application challenges in this space are reducing wiring and detecting error. Since cars are becoming equipped with more and more cameras, reduced wiring is needed to keep costs and weight down. These cameras also provide important safety information, so error detection is vital. The DS90UB903/04 is targeted for infotainment displays, either in the center consol, navigation system, or rear seat entertainment system. These solutions offer 18 bits of color plus synchronization signals sent from the serializer to the deserializer. One application challenge in this space is dealing with touchscreen solutions. The FPD-Link III products provide continual backchannel control, allowing touchscreen information to be fed back with very low latency.
• #7 FPD-Link III serializers and deserializers are used to connect video components of driver assist and infotainment display solutions. The DS90UB901 is used to serialize the RGB inputs from a camera imager in a driver assist system to be sent over long distances on an EMI-friendly single differential pair to the DS90UB902 deserializer. The deserializer then converts the serialized signal back into a parallel RGB signal to be delivered to a display or as a video input to an infotainment system. The DS90UB903 serializer is used in a similar fashion with a video source in an infotainment system to allow long distance transfer of video information. The DS90UB904 deserializer is the matching component that returns the video signal to a parallel RGB video source for use with infotainment displays. The key differences between the two sets of products is that the pair that targets camera systems is limited to a 14-bit color display and has special support to check the validity of data and real time general purpose inputs and outputs (GPIOs) to facilitate camera synchronization, while the pair targeting touchscreen displays has support for an 18-bit color display. The diagram on the bottom shows a typical driver assist system and shows where various serializers and deserializers can be used.
• #8 Before we cover the application challenges, we will briefly explain what exactly is FPD-Link III. These products are 2 pairs of chipsets, the DS90UB901/02 and the DS90UB903/04, that provide sophisticated interface solutions with many technical benefits. These include the high-speed forward channel on serialization and the low speed bidirectional control for inter-integrated circuit (I 2 C) and GPIO signals. The information is transmitted continuously on just one pair. This replaces the multiple interfaces of wires with just a single pair in the system and allows customers to do more with two. The diagram shows a simple explanation of what is going on. Information is coming in at 16 or 21 bits with video data being transmitted in the forward direction. The deserializer then takes the data and sends it to a controller or a display device. At the same time, control data is being sent backward and forward between the serializer and deserializer.
• #9 The top diagram shows a typical application setup for a driver assistance camera system. The image data captured by the camera image sensor is serialized on the left hand side and transferred over to the deserializer in the Electronic Control Unit (ECU) on the right hand side. The microcontroller/processor, DSP or FPGA in the ECU, then processes the image data. In order to enable small form factor image sensors for implementation in for instance, outside mirrors, all the “intelligence” of such systems typically resides in the ECU so the image sensor needs to be configured from the ECU upon system startup. Therefore, the deserializer is taking the control data from the microcontroller and sends it to the serializer over the same two wires of interconnection. The serializer recovers the backchannel control data and passes it to the image sensor for register configuration and dynamic reconfiguration, such as adoptions of exposure time, etc…. Data from the image sensor can also flow in the “forward” direction, i.e. using the same I 2 C interface from the sensor to the serializer. The data is then embedded within the serial video stream and reconstructed on the deserializer I 2 C controller interface again. Thus, National has a true, continuous bidirectional control channel implemented in addition to the conventional video serializer/deserializer function.
• #10 A quick review of the infotainment application is shown on the bottom image. The graphics processor on the right of the image provides data into the interface that supports 18 bits of color. Synchronization signals are also being sent from the serializer to the deserializer over the FPD-Link interface and then going on to the LCD display. At the same time, the graphics controller is able to read touchscreen information from the display side and that's where the I 2 C bidirectional control come into play. This control is being sent over the same set of wires that the video data is being sent in. Therefore, there is no need for a separate control channel between the host side and the display.
• #11 The driver assist application highlights the challenge of having multiple cameras. Here we will discuss how the DS90UB901/02 addresses these challenges. First of all, this pair of products supports 14 bits of color as well as the sync signals. This is ideal for cameras which are typically 10 to 12 bits, while still providing room to expand to 14 bits of resolution for future needs. The 4-bit cyclic redundancy check, or CRC, provides error detection for both the video and control channels. It monitors the information being sent and flags the user if there is any data corruption going in both directions – the video data being sent from the camera to the processor or to any control information. In the driver assist application, these processors are often making very critical-safety decisions based on the data they are receiving, so it is important to have error detection. Programmable GPIOs are available, allowing the camera and host controller to talk to one another. Synchronization signals can be sent from the host to multiple cameras. These GPIOs can also switch at 58 kHz maximum frequency, which allows for a lot of flexibility with transmitting this data. An important feature for camera systems is the I 2 C slave address re-mapping. Some applications require multiple camera devices with the same fixed address to be accessed on the same I 2 C bus. The DS90UB901/02 provides slave ID matching to generate different target slave addresses when connecting more than two identical devices together on the same bus. This allows the slave devices to be independently addressed. Finally, the serializer provides a small footprint. It is in a 32-pin LLP package and is 5 mm x 5 mm, which fits very well inside small camera modules.
• #12 For touchscreen displays, information needs to be from the screen back to the system. The DS90UB903/04 are ideal for touchcsreen applications because of continuous backchannel bidirectional control and 18-bit color support. This is very typical for display applications and this chipset has dedicated inputs for the synchronization signals, each of which is Horizontal Sync, Vertical Sync and Data Enabled. There are dedicated GPIOs and a channel back from the deserializer to the serializer on this chipset. In touchscreen applications, this may be used to interrupt and let the host device know that there is touchscreen information that the host can read over I 2 C. Finally, error checking with CRC over the backchannel is available.
• #13 This slide shows how bidirectional control channel works. The high-speed data is indicated in blue and the low-speed control, backchannel data is shown in orange. What is seen here is that the forward channel driver sends the high-speed data and the forward channel receiver, which is in the deserializer, receives that data at the same time. Then the backchannel driver sends the low-speed data from the deserializer across the same differential pair to the backchannel receiver. The key thing to note here is the continuous transmission of data in both directions over a single pair of wires. That means that both the forward channel driver and receiver are active at the same time that the backchannel driver and receiver are active.
• #14 This page offers more information about the performance of bidirectional control for automotive systems. As mentioned before, this type of control is continuous and EMI friendly. A closer look will help explain this form of control. Again, blue represents the forward-speed, high-speed video data and the orange represents the low-speed, backchannel data. Note the blanking period in the forward channel. Traditionally, video has a blanking interval that occurs with every horizontal line and with every vertical frame. At the end of the line there is a time period when no data is sent and at the end of the frame there is also a time period when no lines of data are sent. This illustrates how CRTs were previously driven, when there was an actual beam drawing the image on the display. At the end of a line, the beam would have to retrace back to the beginning and this becomes the horizontal blanking time. At the end of a frame, the beam would also have to retrace from the lower right hand corner of the display screen to the upper left hand corner to start over and this becomes vertical blanking. This has persisted for legacy reasons into LCD displays where the blanking intervals are not needed or can be very small. This page also shows the forward-channel data illustrating a blanking interval and then showing that the low-speed data is being transmitted continuously. This solution is EMI friendly because one can see that the backchannel data is switching equally and opposite on both the positive and negative ends of the differential pair. This means that no changes are being done to the common mode signal of the differential. Low common mode change means no additional emissions. Finally, this is a low latency solution. The fact that customers can send control data at the same time as forward data means that there is a low waiting period. In addition, there is no waiting for blanking. The I 2 C data and any of the critical GPIO signals are being sent in real time, making this ideal for situations where customers want to synchronize multiple cameras. If customers want to send a synchronization pulse from the host controller to three cameras, this can all happen without being dependent on video timing.
• #15 What is shown here is other bidirectional control systems and some of the restrictions that they may have on their capabilities. These are things that National has chosen not to do, but are being implemented in some other solutions. This page highlights video blanking restriction – sending bidirectional control data only during vertical blanking. At the end of a data frame, the forward high-speed data and the vertical blanking interval is being sent at 60 frames, or sometimes at 30 frames a second for the camera. This means information can only be sent back 30 times a second. The data is also sent back only when no video data is going forward. This then means that one has to use systems that support video blanking. In multi-camera systems, there is also some loss of flexibility for synchronization.
• #16 Here is another solution that National has chosen to avoid. It is using common mode modulation to transmit the backchannel. In this example, backchannel data is transmitted continuously. The common mode signal of the video data is being modulated by the backchannel and this creates common mode modulation (shown in orange). Common mode modulation translates directly into increased emissions. Although one can get continuous backchannel, the limitation here is EMI mitigation and this can be very costly because of the additional board components needed and the scheduling of production release.
• #17 To summarize, the advantages of National’s FPD Link III products – DS90UB901/02/03/04 were highlighted in this presentation. The key takeaway to learn is how bidirectional control works. The idea is that both the video and the I 2 C bidirectional controller are on the same link. Also important is the approach that’s unique to National, the continuous communication in both directions. What this brings is low latency for both the bidirectional control and for GPIO transmissions. This solution meets the EMI requirements that are crucial in automotive applications. The advantage of being able to put all of these capabilities into one wire pair is that it reduces the cost and weight of the cable harness, which is an important part of the system. This technology is also not dependent on blanking periods. This is important because both GPIO signals and control signals are continuously sent from the system host controller to the remote device, and allows a continuous quick stream of I 2 C control data to happen. If video blanking was needed, it would slow down the transactions and would limit the timing of the control signals that could be set to the remote devices. This is especially critical in camera systems where multiple cameras need to be synchronized. Lastly, FPD-Link III is based on a broad family of automotive-grade chipsets with support for multiple resolutions, color depths and applications. Driver assistance application-specific chipsets are available that validate data for high reliability in safety critical applications. The entire family of FPD-Link II and FPD-Link III parts are based on proven automotive EMI solutions and do not require any software drivers, thereby reducing the complexity of designing automotive systems.
• #18 Thank you for taking the time to view this presentation on “ FPD-Link III Serializers & Deserializers” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link right beside the play button on the TechCast portal, or simply call our sales hotline. For more technical information you may either visit the National Semiconductor site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit element14 e-community to post your questions.