Ready for the IoT Era
Responding to demands for high-performance and integrated solutions, sensor manufacturers continue to up their game. And as IoT and intelligent edge applications proliferate, sensors are moving to smaller, low-power designs to meet the new requirements of those systems.
Often the unsung heroes of embedded system designs, sensors do the critical work of interfacing with the real analog world. As the Internet-of-Things (IoT) phenomenon kicks into high gear, sensor innovations have had to keep pace. As result, manufacturers of sensors and sensor interface devices have been hard at work developing highly integrated, high-performance devices.
Because they’re used to working closely with the analog world, microcontroller (MCU) and analog IC vendors are among the leaders of many of the sensor technology and product developments over the past 12 months. While sensors comprise a topic too wide for one article, a snapshot of the latest new sensor products spans a variety of types, including healthcare sensors, temperature sensors, MEMS accelerometer sensors, current sensors, mmWave sensors and more.
SMARTPHONE DESIGN WIN
In March, Maxim Integrated announced that its MAX30101 heart-rate sensor had been integrated into the Raku Raku Smartphone F-01L (Figure 1) from Fujitsu Connected Technologies. The smartphone, which measures heart rate and sleep patterns, can be used for applications such as pedometers. With the MAX30101, the smartphone can also measure stress levels and arterial aging. A popular series for seniors, the Raku Raku Smartphone F-01L was designed so that even those who are using a smartphone for the first time can use it comfortably.
The MAX30101 enables accurate measurements of vital signs using sophisticated algorithms produced by Fujitsu Connected Technologies. By integrating various functions, the module provides a complete system solution to ease the design-in process for mobile and wearable devices. The sensor operates on a single 1.8 V power supply and a separate 5 V power supply for the internal LEDs. The module can be shut down through software with near-zero standby current, allowing the power rails to remain powered at all times. Communication is through a standard I2C-compatible interface, and it operates over the -40°C to +85°C temperature range.
Available in a tiny (5.6 mm × 3.3 mm × 1.55 mm) 14-pin optical module, the device offers very low power consumption of less than 1 mW and ultra-low shutdown current (0.7 μA, typical). The device is easy to implement thanks to the integration of internal LEDs, photodetectors, optical elements and low-noise electronics with ambient light rejection.
TEMP SENSOR FOR IOT
The IoT is driving sensor makers to rethink many of their approaches. For example, temperature measurement is central to the functionality of many IoT implementations, making it imperative that developers integrate temperature sensors that reduce power consumption and lower system voltage in applications. To meet these needs, last October Microchip Technology announced five new 1.8 V temperature sensors, including what it claimed as the industry’s smallest five-channel temperature sensor with standard lead spacing. The EMC181x temperature sensor family also introduces system temperature rate-of-change reporting—a feature that provides advanced warning on how the temperature of a system is fluctuating (Figure 2).
Monitoring temperature at multiple locations with a single, integrated temperature sensor reduces board complexity and simplifies design. The EMC181x temperature sensor family offers a variety of remote channels at 1.8 V operation to fit different design needs, ranging from two to five channels. The family is well suited for applications migrating from 3.3 V systems to lower voltage rails, such as battery operated IoT applications, personal computing devices, FPGAs and GPUs.
The EMC181x family is register and voltage compatible with Microchip’s 3.3 V EMC14xx temperature sensors, making migration to 1.8 V testable and achievable. With the three-channel sensor available in an 8-pin 2 × 2 mm footprint and the five-channel in a 10-pin 2 mm × 2.5 mm footprint, the sensors can also reduce the number of devices needed for remote temperature monitoring.
With the ability to measure the system temperature rate of change, the EMC181x devices offer two-dimensional temperature sensing. In addition to reporting on the regular temperature, the feature notifies customers of the rate of temperature change in a system and shares data that can help better regulate applications. Ideal for closed control loop systems and other applications that prioritize lower voltage rails, the system provides an early notification of rising or falling temperatures, protecting against potential system failure.
COMBINED SENSOR FUNCTIONS
Today’s level of chip integration enables many functions to be combined on a single device, and sensors are riding that wave. In an example along those lines, in April STMicroelectronics (ST) announced its LIS2DTW12 device that combines a MEMS 3-axis accelerometer and a temperature sensor on a single die for use in space-constrained and battery-sensitive detectors such as shipping trackers, wearables and IoT endpoints (Figure 3). The sensing accuracy of 0.8°C offers precision comparable with stand-alone standard temperature sensors.
In addition to enhanced temperature compensation, leveraging the sensor’s high accuracy, the accelerometer benefits from flexibility with 65 different user modes that enable developers to optimize power consumption and noise to meet application-specific requirements. It has user-selectable, full-scale range up to ±16 g and measures acceleration with output data rates from 1.6 Hz to 1,600 Hz.
ST says the device provides about 30% lower package height than other combination sensors, at just 0.7 mm. The LIS2DTW12 allows extra battery capacity for longer runtimes. Power-saving features let devices go even further between charges. These include a 50 nA power-down mode, multiple operating modes down to less than 1 µA, a dedicated internal engine for processing accelerometer signal and a large 32-level FIFO to reduce intervention from the main controller.
The LIS2DTW12 provides 16-bit accelerometer data and 12-bit temperature data through a high-speed I2C/SPI port, and allows single data conversion on demand. The motion engine performs free-fall and wakeup detection, single/double-tap recognition, activity/inactivity, stationary/motion detection, portrait/landscape detection and 6D/4D orientation. ST’s self-test capability is also built-in to verify the sensor is functioning correctly. The LIS2DTW12 is specified from -40°C to +85°C and available in the ultra-thin 2.0 mm × 2.0 mm × 0.7 mm LGA-12 plastic land grid array package.
One area of sensor technology innovation has been in current sensing—an important technology in industrial control systems. For its part, in February, ACEINNA announced its MCx1101 family of ±5 A, ±20 A and ±50 A current sensors for industrial and power supply applications (Figure 4). The company calls the family the first high accuracy wide bandwidth AMR-based current sensors on the market. While there are other AMR-based current sensing solutions on the market, they require a great deal of integration to make them work, says ACEINNA. The MCx1101 devices are plug and play.
The MCx1101 are fully integrated, bi-directional current sensors that offer high DC accuracy and dynamic range. For example, the ±20 A version has a typical accuracy of ±0.6% and are guaranteed to achieve an accuracy of ±2.0% (max) at 85°C. These current sensors also guarantee an offset of ±60 mA, or ±0.3% of FSR (max) over temperature, which means that high accuracy can be achieved over a roughly 10:1 range of currents. This is a roughly 10x improvement in dynamic range vs. leading Hall-sensor-based devices.
These devices deliver a combination of high accuracy, 1.5 MHz signal bandwidth with industry benchmark phase shift vs. frequency and 4.8 kV isolation making them well suited for high- and low-side sensing in fast current control loops for high performance power supplies, inverters and motor control applications. The fast response and high bandwidth of the MCx1101 is also suited for fast switching SiC and GaN based power stages enabling power system designers to make use of the higher speeds and smaller components enabled by wide band-gap switches. Output step response time is 0.3 µs.
The MCx1101 also provides an integrated over current detection flag to help implement OCP (over-current protection)—required in modern power systems. Over current detection response time is a fast 0.2 µs. The family includes ±50 A, ±20 A and ±5 A ranges, and is offered in both fixed gain (MCA1101) and ratiometric gain (MCR1101) versions. It is packaged in an industry standard SOIC-16 package with a low impedance (0.9 mΩ) current path, and is certified by UL/IEC/EN for isolated applications.
CORELESS CURRENT SENSOR
Also rolling out current sensors aimed at industrial applications, Infineon Technologies last month (May) launched a new family of current sensors comprised of precise and stable coreless Hall sensors. They offer flexibility because system developers can individually program product parameters such as the current range, the overcurrent threshold and the output mode. The first product, XENSIV TLI4971, covers measurement ranges from ±25 A to ±120 A (Figure 5). It addresses industrial applications such as electric drives up to 50 kW or photovoltaic inverters. The company says further members of the product family to be released in 2020 will be qualified for automotive applications.
The coreless open loop current sensor offers an accurate and stable current measurement—provided as an analog output voltage. Based on Infineon’s temperature and stress compensation technology, the sensitivity error is as low as 2% at room temperature. It can be reduced below 2% with a single point in-system calibration. Furthermore, differential measurement with two Hall cells ensures high accuracy even in a noisy environment with cross-talk from adjacent current lines or magnetic stray fields.
The TLI4971 has two output pins for fast overcurrent signals. System developers can program the threshold levels of the overcurrent signals and thus adopt them to system requirements without the need of further external components. The signals can be used for pre-warning and system shut-down. In addition, the device also provides a signal in case of an over- or under-voltage condition for the supply voltage.
Because of the coreless concept, the TLI4971 fits into an 8 mm x8 mm x 1 mm leadless QFN type package (TISON-8). The layout of the current rail provides best in class thermal performance for currents up to 120 A, at no extra cost. The device is intended for use in high voltage applications and incorporates galvanic isolation up to 1.1 kV.
Like current sensors, another important technology serving the needs of industrial applications is mmWave sensing. Feeding such needs, in November last year, Texas Instruments (TI) announced its 60-GHz sensor portfolio, touting it as the highest resolution single-chip, CMOS solution for industrial systems. The TI IWR6x mmWave sensors enable industrial automation through on-chip processing capabilities, providing real-time decision-making and signal processing (Figure 6). According to TI, the newest 60- GHz mmWave sensors will be the first to include antenna-on-package offerings, which remove traditional challenges associated with radio-frequency (RF) design while shrinking size up to 75% and reducing overall cost.
With 60-GHz mmWave sensors, engineers can integrate mmWave technology into a wide range of robotics, factory automation and building automation designs while leveraging the ISM band for broad deployment. Built for industrial performance, the high resolution IWR6x sensors provide up to 4 GHz of ultra-wide bandwidth to detect objects and motion up to 16 times more accurately than 24-GHz narrowband solutions.
The IWR6x sensors have integrated processing capabilities that enable the sensor to reduce false positives and make real-time decisions, eliminating the need for an MCU or processor in many systems. These ultra-wideband mmWave sensors detect objects, people, and motion as fine as breathing and typing, with up to 16 times greater resolution than 24-GHz sensors.
Optimized for industrial automation, mmWave technology expands building and factory automation capabilities, enabling smarter people counting, motion detection, robotics, safety guards, vital sign monitoring and more. 60-GHz mmWave sensors improve the accuracy of existing systems by operating in crowded spaces, in various lighting and environmental conditions and through materials such as glass, plastic and drywall.
SENSOR INTERFACE IC
Many sensors interface to the digital world via MCUs. MCU vendors have begun to tailor their solutions for specific sensor needs. An example is the ADuCM355 from Analog Devices, sensor interface IC that enables intelligent electrochemical sensors (Figure 7). According to the company, it is the only solution available to incorporate potentiostat and Electrochemical Impedance Spectroscopy (EIS) functionality on a single chip. The ADuCM355 precision analog MCU with bio-sensor and chemical sensor interface is well suited for applications such as industrial gas sensing, instrumentation, vital signs monitoring and disease management.
The ADuCM355 is an ultra-low power precision analog MCU based on the Arm Cortex M3 processor especially designed to control and measure chemical and biosensors. According to Analog Devices, it is the only solution available that supports dual potentiostat and more than 3 sensor electrodes.
A recent trend in sensor connectivity is the migration of some sensor functions to MCU-based ICs, in some cases eliminating the need for discrete sensor devices. Along just such lines, in April Renesas Electronics introduced its Material Detection Solution (Figure 8), which can detect materials or liquids easily and cost effectively without sensors by connecting electrodes using Renesas’ RX130 capacitive touch-key MCUs. Replacing the sensors with this electrode approach contributes to lower bill of materials (BOM) costs while enabling detection at multiple points using a single chip. This allows industrial equipment, office automation (OA) equipment and home appliance manufacturers to explore detection systems for cost-constrained applications.
Renesas’ touch-key MCUs feature a capacitive touch sensor unit specialized for capacitance measurement with extremely high sensitivity and high noise resistance. This enables the Material Detection Solution to easily detect the presence or absence of a powder such as vacuum cleaner dust, a liquid such as refrigerator and coffee maker, or material such as paper by measuring the capacitance between electrodes to the MCU. The increase or decrease of the powder, liquid, or material will change the capacitance value between the electrodes.
As sensor-based technology proliferates in industrial equipment, OA equipment and home appliances, the demand for different types of sensor solutions is rapidly increasing to address diverse sensing needs, says Renesas. Applications require fine-grained sensing for predictive maintenance capabilities. Although these applications can be implemented by using various types of sensors, such as pressure sensors for detecting physical objects, photosensors, IR sensors and CMOS sensors, the use of multiple sensors creates additional cost and heavy development burdens.
To achieve sensor-less physical object detection easily and cost-effectively, the system connects two thin-film electrodes and measures the capacitance between those electrodes using one of its touch-key MCUs. Changes in the measured materials are determined by detecting the change in capacitance between the electrodes. In addition to eliminating the need for sensor evaluation and operating condition determination, the initialization and sensitivity adjustments can be easily performed using the development support GUI tool available for capacitive touch sensor systems.
Analog Devices | www.analog.com
ACEINNA | www.aceinna.com
Infineon Technologies | www.infineon.com
Maxim Integrated | www.maximintegrated.com
Microchip Technology | www.microchip.com
Renesas Electronics | www.renesas.com
STMicroelectronics | www.st.com
Texas Instruments | www.ti.com
PUBLISHED IN CIRCUIT CELLAR MAGAZINE • JUNE 2019 #347 – Get a PDF of the Issue