Completely Autonomous Radar Sensor for Smart Motion Sensing

By: Bernd Kohler, Infineon Technologies

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Autonomous Radar Sensor

Security systems, automatic doors, smart lighting control and other features of a smart building would not be possible without reliable motion sensors. PIR (passive infrared) 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 which 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. A better solution for more demanding environments would be radar sensors 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 often around 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 since it does not create any optical image of the sensed environment like time of flight (ToF) or camera sensors do. Hence, radar sensing can be completely anonymous.

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. But 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 new opportunities in factory automation, autonomous navigation, cobots or 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 (Fig. 1.)

Industrial radar device forecast
Figure 1: Industrial radar device forecast

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 (Fig. 2) is Infineon’s most integrated and smallest 60 GHz radar sensor. With a size of only about a tenth of a 1 cent coin, the autonomous motion sensor can be easily integrated inside the end product, also because it operates through non-conductive materials. Therefore, the sensor enables seamless integration of radar technology in our day-to-day lives.

Infineon's completely autonomous BGT60LTR11AIP
Figure 2: Infineon’s completely autonomous BGT60LTR11AIP

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 external microcontrollers. 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 m with an 80° field of view. The power consumption remains below 5 mW due to duty-cycling implementation and it can even be lower than 2 mW in certain settings.

Compared to 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. In addition, the sensor can be integrated into systems like laptops, tablets, TVs, speakers, thermostats, etc. 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.

User-friendly and low-power chip

Figure 3 shows the block diagram of the BGT60LTR11AIP MMIC. The integrated voltage-controlled oscillator (VCO) generates the high-frequency signal, which is stabilized by a phase-locked loop (PLL). Moreover, the transmitter section consists of a medium power amplifier (MPA) with configurable output power. It can be controlled via the serial peripheral interface (SPI), while integrated power detectors monitor the transmitted power.

BGT60LTR11AIP MMIC block diagram
Figure 3: BGT60LTR11AIP MMIC block diagram

The chip features a low-noise quadrature receiver stage, where the receiver uses a low-noise amplifier (LNA) 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 (PPF) generates quadrature local oscillator signals for the quadrature mixer.

The integrated analog base band (ABB) units consist of a sample-and-hold (S&H) circuit for low-power duty-cycle operation followed by an externally configurable high-pass filter, a variable gain amplifier (VGA) stage and a low-pass filter. The integrated detectors are comparators generating 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 2-layer laminate package, the small 3.3 x 6.7 x 0.56 mm³-sized MMIC includes integrated antennas, which eliminates 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 4 shows a PCB with the BGT60LTR11AIP MMIC. The supporting circuitry on it includes a low-noise voltage regulator (LDO), 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, the red LED turns on when a target is moving away from the sensor and turns off when it is moving towards the sensor.

Shield with supporting circuitry to the BGT60LTR11AIP MMIC
Figure 4: Shield with supporting circuitry to the BGT60LTR11AIP MMIC

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 as well as initial product feature evaluations.

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. The following table displays the QS parameter settings:

Experienced radar users can utilize the semi-autonomous and SPI mode by changing the operation mode with a QS1 pin. For example, in 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 (radar GUI) to display and analyze acquired data in time and frequency domain.

Summary

The smart and cost-effective 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 or put them to sleep based on motion/no-motion detection.

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

About the author:

Bernd Kohler

Bernd Kohler
has a background in physics (M.Sc.) and completed an MBA before he joined Infineon’s Radar team in 2020. As product marketer & manager, he is responsible for a wide range of Infineon’s 24 GHz radar sensors as well as the new 60 GHz smart motion sensor BGT60LTR11AIP. Bernd is mainly driving all industrial radar applications including camera and security systems, lighting systems as well as smart home & smart building applications.