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Completely Autonomous Radar Sensor for Smart Motion Sensing

By Bernd Kohler and Arushi Jain, Infineon Technologies AG   02.23.2021 0

Security systems, automatic doors, smart-lighting control, and other features of a smart building would not be possible without reliable motion sensors. Passive infrared (PIR) sensors are commonly used despite their significant disadvantages. Infineon has developed a compelling and cost-effective replacement to make motion sensing smarter: A one-package radar-sensing solution that enables radar technology for everyone.

Widely used PIR sensors detect the infrared radiation of a person, an animal, or an object at mid-infrared wavelengths. However, with rising temperatures, their reliability decreases dramatically. It is therefore recommended not to install them near heat sources or use them in high ambient temperatures. For more demanding environments, radar sensors are a better solution, as they are less temperature-dependent.

Another advantage of radar sensors is their superior sensitivity. PIR sensors can mainly detect larger movements along the tangential direction with a minimum speed of about 1 m/s. As a consequence, PIR sensors are ineffective for stationary and radial movement detection. In contrast, radar sensors detect the slightest movement of the human body, be it typing, speaking, or even breathing. Furthermore, you can get the direction of motion, velocity, or even exact position of a target, depending on the radar chip configuration.

Beyond that, radar sensing protects privacy, because it does not create any optical image of the sensed environment as time-of-flight or camera sensors do. Hence, radar sensing can be completely anonymous.

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By Shingo Kojima, Sr Principal Engineer of Embedded Processing, Renesas Electronics  03.26.2024

Given its unique features and benefits, radar has been used for decades in defense, security, and aerospace, as well as applications like weather monitoring or traffic control. In the industrial area, radar was limited to level/ground probing, maritime navigation, and motion sensors for automatic doors. Yet in the past few years, the technology has advanced significantly and will now create opportunities in factory automation, autonomous navigation, cobots, and commercial drones for industrial inspection. According to Yole,1 the market for industrial radar applications is expected to exceed 10 million devices within the next five years, with basic motion/presence detection as the predominant use case (Figure 1).

Figure 1: Industrial radar device forecast (Source: Yole Développement)

However, radar technology still requires a considerably high level of know-how in radio-frequency engineering, antenna design, and signal processing — all areas where Infineon Technologies has achieved a high level of expertise over the last decade. As the market leader in radar chips, Infineon has developed a product that combines all advantages in a fully integrated microwave motion sensor, thus creating the most user-friendly radar solution so far.

First completely autonomous and easy-to-use motion sensor

The BGT60LTR11AIP (Figure 2) is Infineon’s most integrated and smallest 60-GHz radar sensor. With a size of only about one-tenth of a penny, and because it operates through non-conductive materials, the autonomous motion sensor can be easily integrated inside the end product. Therefore, the sensor enables seamless integration of radar technology in our day-to-day lives.

Infineon’s radar sensor is a fully integrated microwave motion sensor with built-in motion and direction-of-motion detectors as well as antennas-in-package (AIP). A state machine enables operation of the device without an external microcontroller. Two integrated detectors provide two digital output signals — one indicating motion and the other indicating the direction of motion (approaching or departing) of a target. Instead of the usual processing of the radar raw signal, these two signals can be used directly. In this autonomous mode, the sensor detects a person up to 5 meters away with an 80° field of view. The power consumption remains below 5 mW because of duty-cycling implementation, and it can even be lower than 2 mW in certain settings.

Figure 2: Infineon’s completely autonomous BGT60LTR11AIP

Compared with common radar sensors, the BGT60LTR11AIP specifically addresses smart-building and smart-home applications. Without great effort, the sensor adds “smartness” to traditional motion-sensing applications like lighting systems, automated door opening, or security systems, including intruder alarms and cameras (Figure 3).

In addition, the sensor can be integrated into systems such as laptops, tablets, TVs, speakers, and thermostats to “wake” them up based on motion or direction-of-motion detection. It can also put devices to sleep or into auto-lock when no motion is detected for a defined amount of time to save energy, increase lifetime, protect privacy, and enhance the user experience overall.

Figure 3: The BGT60LTR11AIP adds a smart motion-detection feature to many
smart-home devices.

User-friendly and low-power chip

Figure 4 shows the block diagram of the BGT60LTR11AIP monolithic microwave integrated circuit (MMIC). The integrated voltage-controlled oscillator (VCO) generates the high-frequency signal, which is stabilized by a phase-locked loop. Moreover, the transmitter section consists of a medium-power amplifier with configurable output power. It can be controlled via the serial peripheral interface (SPI), while integrated power detectors monitor the transmitted power.

The chip features a low-noise quadrature receiver stage, wherein the receiver uses a low-noise amplifier in front of a quadrature homodyne down-conversion mixer, to provide excellent receiver sensitivity. Derived from the internal VCO signal, an RC poly-phase filter generates quadrature local oscillator signals for the quadrature mixer.

The integrated analog baseband units consist of a sample-and-hold circuit for low-power duty-cycle operation, followed by an externally configurable high-pass filter, a variable-gain amplifier stage, and a low-pass filter. The digital detectors generate pulses based on target movements in front of the radar. For maximum flexibility and robustness against false alarms, the detector circuitry offers a user-configurable hold time, a hit counter, and a detection threshold.

Within its two-layer laminate package, the small, 3.3 × 6.7 × 0.56-mm³ MMIC includes integrated antennas, eliminating the complex antenna design at the user end. PCB designs with this MMIC do not require special base materials, so customers can use standard FR4 materials. Figure 5 shows a PCB with the BGT60LTR11AIP MMIC. The supporting circuitry on it includes a low-noise voltage regulator, a crystal oscillator source of 38.4 MHz for the reference clock, and external capacitors. The output of the sensor is illustrated by two LEDs: A green LED lights up when a target is detected, while the red LED turns on when a target is moving away from the sensor and turns off when it is moving toward the sensor.

This shield demonstrates the features of the BGT60LTR11AIP MMIC and provides a complete turnkey radar solution. By connecting a power supply to VCC and GND castellated holes, it is possible to “plug” the MMIC motion sensor into an existing system. Hence, the all-in-one solution enables fast prototyping, simple system integration, and initial product feature evaluations.

Figure 4: BGT60LTR11AIP MMIC block diagram

Quad states allow easy switch between autonomous mode and SPI mode

Four quad-state (QS1–4) input pins allow flexible performance parameters even when the sensor is running in autonomous mode. For instance, the user can easily select between multiple threshold values at QS2 to increase or reduce the detector sensitivity and, therefore, the detection range. The following table displays the QS parameter settings:

Experienced radar users can utilize the semi-autonomous and SPI modes by changing the operation mode with a QS1 pin. For example, in the case of an already existing microcontroller, the chip parameters can be set precisely via SPI, but the detection can still be done via the integrated detectors. In the completely non-autonomous SPI mode, the interface can also be used for extracting the radar raw data for signal processing or for developing customized algorithms.

Therefore, the shield can also be attached to an Arduino MKR board or an Infineon MCU7 radar baseboard.

Infineon’s toolbox supports this platform with demonstration software and a radar graphical user interface to display and analyze acquired data in time and frequency domain.

Figure 5: Shield with supporting circuitry to the BGT60LTR11AIP MMIC

Summary

This radar-based motion sensor developed by Infineon is suitable for various motion-sensing applications such as lighting control, automated door opening, security systems, and other typical smart-home devices. The user-friendly radar solution can be applied directly to products to add radar functionality quickly and to add smartness to traditional applications to wake them up or put them to sleep based on motion/no-motion detection.

Integrated detectors and a state machine enable autonomous operation with digital output signals in addition to the semi-autonomous and SPI modes. Hardware preset pins, so-called quad states, allow users to easily set radar operation parameters even in the completely autonomous mode of the chip. With all of these features plus low power consumption, the BGT60LTR11AIP is a compelling, smart, and cost-effective replacement for conventional PIR sensors.

References

1Yole, “Status of the Radar Industry,” 2020.

 

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