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Basics of automotive instrument cluster architectures (Part 1)

08 Dec 2014  | Deepak Mahajan, Vikas Agarwal, Arjun Pal Chowdhury

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There can be a number of extensions to the display controller interfaces and capabilities to support wide range of flat panel or curvature displays available in market based on product requirement. A few of them include:
It can also interface with on-chip TCON (Timing Controller) to generate the timing signals and to directly drive the row and column drivers of display panels via RSDS (Reduced Swing Differential Signaling) pads. RSDS is having a voltage swing of 200mv and is similar to the Low Voltage Differential Signal (LVDS). RSDS interface signals instead of TTL based signals leads to the reduction of EMI in between the Panel Timing Controller and the Column drivers. The reduced signal swing level of RSDS also results in low power consumption and EMI levels as compared to TTL based interface.

It can also support the Open LVDS(Low Voltage Differential Signaling) Display Interface (OpenLDI) specification through an on-chip converter which converts the digital RGB into OpenLDI-compatible format of 4-data-pair and 1 clock pair LVDS interface output. It minimises the number of wires that must be used to connect the display source and display device while also minimising radiated emissions and susceptibility to electromagnetic interference. This enables the display controller to support a wide range of display formats, refresh rates, and pixel depths.

One of the recent and latest features that have come up is of the head-up display (HUD). A head-up display is a display technology projecting the content directly on the windscreen of the car. As the windscreen is not a flat projection area, the image gets distorted. So to compensate this effect, in-line, real-time warping is being performed on the content to be displayed using the graphic accelerator or dedicated hardware. The fundamental advantage of such display is that the information is presented in the normal field of view of the driver looking onto the street. It will enhance safety while delivering navigational and other critical information to drivers such as speed, fuel level, etc. Head-up displays are usually used in combination with a TFT display in the instrument cluster.

Video input unit
The Digital Video Input module is mainly used to take a compatible video stream or other supported formats as input from an external interface like reverse camera, driver monitor camera, etc. and then enabling a set of processing on the captured digital video to finally get it displayed through the Display Controller to TFT/LCD Display for the user/driver. Different kinds of processing on video include brightness adjustment, contrast adjustment, up-scaling or down-scaling of the picture, input data format conversion from one colour space to other, horizontal mirroring for reverse camera adjustment, etc.

In case of analogue camera input, the picture information is transmitted to some off-chip Video ADC which converts the signal to Digital and feed to this module. Usually RCA composite cables are used to connect the analogue camera to the converter.

RLE decoder
This module is used to decode data that has been compressed using a Run Length Encoding (RLE) scheme. Run length encoding is a simple scheme that compresses data based on repetition of consecutive entries. Each block of data is preceded by a command byte that indicates whether compression is active and if so how many copies of the next data are required.

The RLE decoder performs extraction of run length encoded data and is optimised for extraction/decompression of graphic images and put it back in local memory for Display Controller to display. Data are fed to RLE typically using DMA and decompressed data are fetched typically by DMA. Any portion of a graphic can be decoded based on given start-pixel location and given end-pixel location. Apart from lossless decompression, it also supports the partial image decoding feature.

Segmented LCD controller
This controller is equipped with multiple Front and Back plane drivers with the backplane drivers remapping feature to drive the external segmented LCD to display clock, odometer, trip meter, etc. or other related information. It is configurable to support multiple varieties of segmented displays. This module is also responsible for On-chip generation of all output voltage levels that are required to drive the display segments. It also supports programmable frame clock generator, programmable bias voltage level selector, programmable output current and an optional output current boost during transitions for displays along with the contrast adjustment feature. In a low cost solution, segmented LCD display can be an alternate option to graphical TFT display.

In our modern age with a highly featured digital solution, all existing luxury is transforming into necessity and creating scope for new innovation. Hence the immediate challenge is to provide integrated solutions that are cost effective and technically advanced to fulfil market requirements. The automotive cluster has transformed from analogue gauges to digital displays to integrated cluster infotainment solutions. The future trend will be to move towards a highly integrated solution where basic cluster, infotainment, advanced driver assistance will all be integrated in a single device. Hence it is very important to understand the basic architecture to know how they can be used to create an integrated cost-effective solution for the future.

About the authors
Deepak Mahajan, Vikas Agarwal, Arjun Pal Chowdhury contributed this article.

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