Advanced Driver Assistance Systems (ADAS) Camera

Design Considerations

Automotive Vision Control systems process digital information from sources like digital cameras, lasers, radar and other sensors to perform tasks such as lane departure warning, drowsiness sensors, or parking assistance. The processed information can be displayed on screens or announced via acoustical warning signals.

Power Management: The power supply is connected to the 12V or 24V board net and regulates down/up to voltages for DSP, uC, memory and ICs and functions like stepper motors, communication interfaces, display biasing and back lighting. The need for many different power rails makes the design of the power supply a critical task when trying to design for size, cost and efficiency. Linear regulators with low quiescent current help reduce battery leakage current during standby operating modes (ignition off), are load dump voltage tolerant for directly battery connected devices, and need low drop out and tracking for low battery crank operation.

Beyond providing increased conversion efficiencies, switching power supplies provide EMI improvement with slew rate control of the switching FET, Frequency hopping, spread spectrum or triangulation method for attenuation of peak spectral energy, Low Iq, soft start for power sequencing and in rush current limitation, Phased switching for multiple SMPS's regulators to minimize input ripple current and lower input capacitance, higher switching frequency for smaller components (L and C's), and SVS functions for brown out indications.

Communication Interfaces: Allow data exchange between independent electronic modules in the car, the remote sub modules of the infotainment system as well as external devices like USB memory or video sources. High Speed CAN (up to 1Mbps, ISO 119898) is a two wire, fault tolerant differential bus. With a wide input common mode range and differential signal technology it serves as the main vehicle bus type for connecting the various electronic modules in the car with each other. LIN supports low speed (up to 20 kbps) single bus wire networks, primarily used to communicate with remote sub functions of the infotainment system. LVDS interfaces are used to transfer large amounts of data via a high speed serial connection to an external location like a video screen or from the video source (digital camera chip).
Display: Some automotive vision systems have displays supporting functions like parking assist. Depending on the display type, a power supply solution for the display biasing is required on top of the LED or CCVF drivers for backlighting. The video information is either sent directly from the uC or via a LVDS interface depending on the size of the display.

Microcontrollers: General purpose uC handle system control functions as well as communication with other modules in the car. The core digital function is the DSP, processing the data from the digital input source (e.g. CCD camera). Depending on the required performance simple driving of a screen to complex digital algorithms for e.g. pattern recognition can be needed. The MCU also needs to high enough performance speed to servicing the stepper motors in real time.

The Safety MCUs offer an ARM Cortex-R4F based solution and are certified suitable for use in systems that need to achieve IEC61508 SIL-3 safety levels. These MCUs also offer integrated floating point, 12 bit ADCs, motor-control-specific PWMs and encoder inputs via its flexible HET Timer co-processor. Hercules Safety MCUs can also be used to implement scalar and vector-control techniques and support a range of performance requirements.

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