Integrated Radar Sensors Steer the Way for ADAS

Texas InstrumentsBy Jack Browne, Technology Editor
[Sponsored by Texas Instruments]

Various electronic sensor technologies are making automobiles safer, with and without help from a driver. A number of different technologies are currently used within Advanced Driver Assistance System (ADAS) automotive safety systems, including those using radar, laser, light detection and ranging (LiDAR), infrared (IR), and ultrasonic devices. Radar technology has been widely adopted by automobile manufacturers for its high resolution at 24 and 77 GHz and its dependability under many different driving conditions, including fog, rain, and snow. As ADAS systems become part of virtually every car on the road, automotive system designers look to follow the same trends that drive many other areas of electronics: achieving smaller solutions at lower costs and with less power consumption through higher levels of integration. For automotive radar systems, increased integration entails transforming a handful of electronic devices down to one, with analog, RF, and digital circuitry included on a single packaged integrated circuit (IC) to perform the following functions:

1. Sensing

Electronic devices such as millimeter-wave automotive radar systems are helping to evolve the automobile into a fully autonomous, self-driving vehicle. The Society of Automotive Engineers (SAE) International has actually defined six levels of driving automation, from level 0, with no automation, to level 5, with full automation and self-driving functionality. Different types of sensors within a car, including millimeter-wave radar transceivers, transmit beams of energy off different objects within their field of view, such as pedestrians or other cars, and detect the reflected returns from the illuminated objects. Sensor outputs are sent to one or more microprocessors to provide information about the driving environment for assistance with driving functions such as steering and braking to prevent collisions and accidents.

Auto Micro example

Radar and other forms of EM sensors are used in an ADAS vehicle to detect fixed and moving objects at different distances around the perimeter of the vehicle.

Multiple sensors are needed for 360-deg. detection around an ADAS automobile. Often, this involves sensors based on different forms of electromagnetic (EM) energy. Automotive radar sensors typically incorporate multiple transmitters and receivers to measure the range, angle, and velocity of objects in their field of view. Different types of radar systems, even different operating frequencies, have been used in ADAS systems, categorized as ultra-short-range-radar (USRR), short-range-radar (SRR), medium-range-radar (MRR), and long-range-radar (LRR) sensors or systems.

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The different types of radar serve different purposes, such as USRR and SRR sensors for blind-spot-detection (BSD) and lane-change-assist (LCA) functions and longer range radars for autonomous emergency braking (AEB) and adaptive-cruise-control (ACC) systems. USRR and SRR sensors once typically operated within the 24-GHz frequency band, with MRR and LRR sensors in the 77-GHz millimeter-wave frequency range. Now, however, the frequency band from 76 to 81 GHz is typically used, due to the high resolution at those higher frequencies—even for shorter distance detection.

2. Signal Generation/Conversion

Whether for automotive or military applications, radars are complex systems which require a number of different electronic subsystems. Signals for transmission must be generated with the aid of a stable local oscillator (LO) or frequency synthesizer and amplification, while returning reflected signals must be downconverted by means of mixers and low-noise amplifiers (LNAs) to a lower intermediate frequency (IF) that can be sampled and digitized by an analog-to-digital converter for analysis of radar returns within a microprocessor. At one time, a millimeter-wave radar system would have been implemented entirely with separate components for each function. But for both military and automotive applications, decreased size, weight, and power (SWaP) are key factors driving the increased integration of millimeter-wave radar solutions.

Automotive radar systems for ADAS applications typically employ multiple transmitters and receivers to illuminate and detect multiple targets. The need to save power consumption and size in automotive applications favors the use of low-power integrated circuits (ICs) to provide the different radar system function blocks, such as RF/IF circuits, digital signal processing (DSP), and microprocessors. Traditional ADAS radar system implementations have employed multiple packaged ICs on a common motherboard. While it is possible to achieve low-power operation with such a design approach, demands for increased ADAS functionality in smaller-sized, lower-power solutions are driving the development of automotive radar systems contained within few numbers of packaged ICs or even, when possible, complete radar systems within a single IC. This includes all the functions required to support multiple radar transmitters and receivers, including 77-GHz power amplifiers (PAs), frequency mixers, LOs, and LNAs.

3. Processing

Due to the advanced modulation formats used with automotive radar sensors, including frequency-modulated continuous-wave (FMCW) modulation, a great deal of DSP and microprocessor power is required to implement the different detection ranges and functions of a fully equipped ADAS vehicle. While highly integrated ADAS millimeter-wave radar systems can save on size, power consumption, and complexity in total number of electronic system components, one of the tradeoffs in applying such a high level of integration can be the lack of flexibility that is possible through the use of an external DSP and/or microprocessor. Some ADAS functionality, in particular for longer detection distances, such as automated highway driving and adaptive cruise control, can benefit from the additional processing power available with an external DSP or microprocessor.

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Bringing It All Together

With the growing number of electronic devices and systems in new car models, semiconductor suppliers designing the different types of sensors, including millimeter-wave radar systems, are pursuing higher levels of integration to save on size and power consumption. In addition, rather than using different ICs for USRR, SRR, MRR, and LRR ADAS functions, ICs capable of multimode operation can simplify the parts counts (and costs) of newer ADAS electronic systems.

In addition to the flexibility provided by multimode radar modules or ICs, further integration can add to the usefulness of an automotive radar solution. For example, a radar system with on-board DSP will also require memory for storage of DSP algorithms as well as acquired data for processing. Integration of functionality such as DSP and/or memory to the same IC containing the millimeter-wave sensors eliminates the need for interconnections between modules or the addition of separate packaged components, which can add significantly to the total power consumption for an ADAS system.

Block Diagram from Texas Instruments

This block diagram shows a high level of integration for a 77-GHz ADAS millimeter-wave sensor system, in which RF/microwave and digital circuit functions are supplied on the same IC. (Courtesy of Texas Instruments)

Automotive radar systems require a great deal of signal processing to minimize the effects of interference, such as clutter from ground reflections. In addition, as the number of ADAS-equipped vehicles increases, the number of radar signals in the operating environment will increase, with greater potential for interference. Different applications and operating environments will require more or less signal processing power, there will still be a need for the flexibility provided by external DSPs and microprocessors in ADAS system in the unforeseeable future.

The growing popularity of vehicles with ADAS electronic systems is obvious, since these smart-sensor technologies provide safer rides. As the amount of electronic systems within automobiles increases, including the different types of sensors and the communications network and microprocessors needed to coordinate them with automotive mechanical systems, the trend points to further integration of electronic devices, including component technologies such as millimeter-wave circuits, DSPs, and microprocessors that previously had only been available as separate components.

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