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Basics of automotive instrument cluster architectures (Part 2)

28 Sep 2015  | Deepak Mahajan, Vikas Agarwal, Arjun Pal Chowdhury

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Real time data, for example, a reverse camera stream will get buffered into the video input unit for scaling, brightness adjustment, etc. and then put into Graphics RAM/DRAM. It can then be further processed by the graphics application processor and stored back into DRAM/Graphics RAM. Finally, it can be routed to the LCD display by the display controller.

Low power mode requirements in a cluster device
The key challenge of a cluster device is to minimise the average power consumption when the car is idle, improving the battery lifetime of the car. When the car is in an idle state, i.e. the ignition key is disengaged, the cluster ECU must perform basic housekeeping functionality, which is activated periodically, such as the monitoring of the onboard power supply, performing basic computational tasks on the monitored inputs such as filtering of results, making a comparison against historic results, and more. Keeping the time clock on and calibrating the clock used for RTC are also common housekeeping functions performed.

An intelligent device must ensure bare minimum power consumption of the device during the idle phase. Standby mode or deep sleep mode are generally used to support this requirement. It is incumbent on the designer to keep bare minimum functionality ON in standby mode to minimise the leakage power of the device and at the same time ensure the seamless execution of housekeeping functionality.

Most cluster functionalities such as display, motor control, and graphics core or real-time processors are not required to operate while the car is idle. Hence a power supply can be permanently switched off. In order to enable housekeeping functionality some basic modules like ADC, SPI, timers, and a small processor must be periodically enabled. Hence, the device can have a provision to switch ON and OFF the functionality required for housekeeping. There are few modules that always need to be enabled. For example, the Real Time Clock (RTC) module and some memory array which keep some important data and parameters for housekeeping functionality needs to be always ON.

The above is a conceptual diagram of a cluster device where the partition is based on low power mode requirement. When the ignition key is engaged, i.e. the device is in full power mode, all the switches (S1 and S2) are closed. In car idle state, S1 will remain open permanently and S2 will be open and closed periodically during housekeeping functions. This architecture will help to improve the average power consumption of the device significantly in a car idle state.

Today, 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, and 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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