Analysis of representative automotive ultrasonic and millimeter wave radar products

Radar systems are often associated with military projects such as aircraft, but they are now rapidly making their way into civilian applications, including commercial vehicles. Millimeter wave (mmWave) radar systems are being integrated into new vehicles as part of advanced driver assistance system (ADAS) electronics to provide a safer driving experience. While fully autonomous “self-driving” cars may still be years away, ADAS features such as blind spot detection and collision avoidance can protect drivers now. Low power, high frequency radar detection is essential to enable all object detection, ultimately creating a safer driving experience.

Millimeter wave radar technology, LiDAR technology, and cameras are three important sensor technologies that improve ADAS functions. The frequency of automotive radar is still mainly concentrated at 24 GHz, but 77 GHz is the technology that major manufacturers are focusing on today. Frequency modulated continuous wave (FMCW) radar integrated circuits (ICs) based on millimeter wave frequencies are being launched. Radar can distinguish between stationary and moving targets, detect multiple targets at the same time, and even calculate the relative speed of the detected vehicle through its Doppler frequency shift.

The radar operates with stable accuracy in a variety of lighting and weather conditions, day and night, and over a wide temperature range. Sensor fusion performed by the ADAS processor can use data from three types of sensors to create a 3D image of detected targets. Advances in sensor fusion technology, especially utilizing radar in two frequency ranges, are clearing the way for the generation of 4D radar-based data that can be used for target range, angle, speed and elevation required for future autonomous driving control.

Radar receivers, transmitters, and transceivers for ADAS are typically implemented as highly integrated monolithic microwave integrated circuits (MMICs) using high-frequency/high-speed semiconductor technologies such as silicon germanium (SiGe) or silicon (Si) BiCMOS. MMICs typically support modular functionality, with separate MMICs for transmit and receive functions, or as transceivers with single or multiple transmit and receive channels per chip.

Whether operating at 24 GHz or 77 GHz, ADAS radar circuit and system designers can package major system functional blocks (such as microprocessors, digital signal processing (DSP), and power supplies) into the same IC to save space. The central ADAS processor performs sensor fusion by combining radar data with LiDAR and camera imaging data to create a 360-degree image.

1. ADAS-equipped vehicles rely on sensor data fusion from radar, LiDAR, and camera-based systems to create a 360-degree field of view of object detection. (Courtesy of Xilinx)

MMICs for ADAS mmWave radars are available for 24 GHz and 77 GHz short-range radars (SRRs) that can detect about 20 m, medium-range radars (MRRs) about 60 m, and long-range radars (LRRs) about 200 m or more. Current 24 GHz radar MMICs operate in the industrial, scientific, and medical (ISM) band of 24.00 to 24.25 GHz and have been used in non-automotive industrial and medical applications, including intruder detection in warehouses and heart rate detectors.

Now, government spectrum regulators, including the U.S. Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI), plan to free up more bandwidth around 24 GHz for ultra-wideband (UWB) radars, which can target objects with improved resolution than is currently possible.

As most drivers expect new cars to provide ADAS electronic solutions for improved safety, the demand for automotive mmWave radar solutions is increasing. More semiconductor suppliers, including some that are already producing 24 GHz ADAS radar ICs, are developing radar ICs for 77 GHz (76 to 81 GHz), 5 GHz bandwidth for SRR, MRR, and LRR ADAS applications.

Scanning radar solutions

Highly integrated ICs for automotive radars targeting 24 GHz ISM band systems, such as Infineon’s BGT24A family of ADAS radar transceiver and receiver ICs.

Members of the BGT24A family include the BGT24ATR11, a 24 GHz radar transceiver with one transmit channel and one receive channel. The BGT24ATR12 has one transmit channel and two receive channels; the BGT24AR2 and BGT24AR4 have two and four receive channels, respectively; and the BGT24AT2 has two transmit channels that can be added to either transceiver to enhance situational awareness. These ICs are available in VQFN packages (Figure 2) for easy mounting on a PCB.

2. The 24 GHz radar sensors of the BGT24A series are MMIC transceivers with different transmitter and receiver combinations. (Courtesy of Infineon Technologies)

The BGT24ATR11 is an MMIC transceiver with a single receive and transmit channel designed for frequencies from 24.00 to 24.25 GHz. It is AEC-Q100 qualified and has been used in many industrial and medical applications. The MMIC is based on a 0.18μm bipolar SiG process with an upper frequency limit of 200 GHz, centered around a low-noise, 24 GHz voltage-controlled oscillator (VCO). The phase noise of the VCO is -85 dBc/Hz at 100 kHz offset from the carrier.

The MMIC transceiver contains a switchable prescaler with 1.5 GHz and 23 kHz outputs. It also provides a 24 GHz local oscillator (LO) output signal, typically 0 dBm, to drive other functions. The transmit section of the MMIC produces a typical power of +9 dBm to the antenna; the output power can be controlled between 3 and 9 dB.

The transmitter features the fast on/off switching required for radar use, typically 500 ns, and controls spurious outputs to -30 dBm or less in off mode. The homodyne receiver supports many different 24 GHz ADAS radar system configurations with a mid-frequency (dc) range from dc to 10 MHz. The 24 GHz radar transceiver is available in a compact, RoHS-compliant VQFN package and consumes only 500 mW of power from a +3.3 V dc supply.

The STMicroelectronics STRADA431 has one transmit channel and three single-ended receiver channels, each with its own variable gain amplifier (VGA), and is an AEC-Q100-compliant 24 GHz ADAS transceiver that is also built around a low-noise 24 GHz VCO. Typical phase noise is −75 dBc/Hz offset 100 kHz relative to the carrier. It is packaged in a 6×6mm QFN package, powered by a +3.3V DC supply, and controlled by a four-pin SPI interface. The MMIC has on-board power and temperature sensors, and its single-channel transceiver can provide +13 dBm differential output power at 24 GHz. It has a switchable/selectable IF filter and has a receiver conversion gain of up to 60dB.

Analog Devices, a longtime IC supplier, offers 24 GHz ICs for commercial and industrial safety systems that can also be used in ADAS radars. Like many semiconductor suppliers, the company also offers evaluation boards to simplify initial testing of radar chips.

The EV-TINYRAD24G radar evaluation module and EV-RADAR-MMIC2 evaluation board are populated with the ADF5901 24-GHz transmit IC and the ADF5904 24-GHz receive IC, along with the ADF4159 phase-locked loop (PLL) IC. The ICs can work together with different mmWave antennas. The evaluation module (Figure 3) is equipped with a phased array antenna with a multiple-input, multiple-output (MIMO) configuration, which allows the use of multiple small antenna elements in an array to form an antenna radiation pattern for both transmit and receive functions.

3. For ease of evaluation, separate 24 GHz transmit and receive ICs are mounted on a compact EV-TINYRAD24G PCB. (Courtesy of Analog Devices)

These highly integrated devices implement effective radar functions in a small 5 × 5 mm LFCSF package. For example, the ADF5901 provides dual 24 GHz radar transmit channels with onboard power amplifiers and 24 GHz VCOs. The VCOs also provide LO signals for other receiver functions. The IC contains various digital circuits, such as auxiliary analog-to-digital converters (ADCs), as well as temperature sensors and power control circuits for each transmit channel. A simple four-wire interface controls all on-chip registers.

Higher frequency

Since the available ISM bandwidth at 24 GHz is currently limited to 250 MHz, many circuit and system developers find the larger available bandwidth near 77 GHz (and the higher resolution at smaller wavelengths) attractive for ADAS radars. Many semiconductor processes used for 24 GHz ADAS radar chips support 77 GHz devices with similar transmitter, receiver, and transceiver architectures.

For example, STMicroelectronics manufactures its dual-band, 76 to 77 GHz and 77 to 81 GHz STRADA770M ADAS radar transceiver on SiGe BiCMOS. The tiny transceiver integrates four single-ended 50Ω receiver channels (each with a high-resolution ADC) and three single-ended 50Ω transmitter channels. The transmitter channels include a linear frequency modulation modulator and linear frequency modulation, and the integration of multiple functions is contained in a single wafer-level BGA package measuring only 9 × 9 mm.

The STRADA770M radar transceiver includes an integrated low phase noise oscillator designed to operate with a 40 or 50MHz crystal reference. Typical phase noise is −95 dBc/Hz at 1 MHz offset from the 77 GHz carrier. The transceiver typically provides +13 dBm transmit power in the 76 to 77 GHz range and +10 dBm in the 77 to 81 GHz range. It achieves up to 75dB of receiver conversion gain, adjustable in 3dB steps over a 30dB range. The densely packed IC features an onboard linear frequency chirp sequencer and FMCW linear frequency chirp modulator, as well as a digital slave interface that can be set for SPI or I2C operation. The MMIC operates from a single +3.3V DC supply.

NXP Semiconductors’ TEF8102 ADAS radar transceiver MMIC (Figure 4) is fabricated on the company’s 20-nm RF CMOS process. The MMIC contains three transmit channels with binary control and output level stabilization, and four receive channels. Each receive channel has a dedicated 12-bit ADC. An onboard waveform generator achieves a typical transmit power of +12 dBm in the 76 to 78 GHz range and +13 dBm in the 78 to 81 GHz range. The four receive channels of the FMCW transceiver provide serial output data, which benefits from the low noise of the waveform generator. Typical phase noise is −86 dBc/Hz or better when offset by 1 MHz from any frequency between 76 and 81 GHz.