We get technical
Sensors | Volume 19
Advancing magnetic sensing
ADI's data acquisition solution shines in advanced lithography chip manufacturing Arduino sample code for SPI absolute encoders
Accelerate your electronics projects
we get technical
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Precision in a flash with direct time of flight sensing
How low-power overmolded reed switches solve vexing position sensing challenges
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How A2L sensors make sure refrigerants don't blow(up)
Advancing magnetic sensing with Allegro MicroSystems’ Tunnel Magnetoresistance (TMR) technology
Special feature: retroelectro Experiments on the effect of a current of electricity on the magnetic needle ADI's data acquisition solution shines in advanced lithography chip manufacturing Take advantage of I3C for faster, simpler, and more flexible IC-to-IC communication
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Arduino sample code for SPI absolute encoders
Learn the fundamentals of signal integrity
Accelerate your electronics projects with Scheme-it and DigiKey’s extensive component catalog
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Editor’s note Welcome to the DigiKey eMagazine Volume 19 – Sensors.
This edition will deep dive into the latest advancements in sensor technologies, data acquisition systems, and communication protocols, all of which are shaping the future of the electronics and semiconductor industries. As the pace of innovation accelerates, understanding these emerging technologies is crucial for both engineers and technologists looking to stay ahead. In this issue, we explore the intricacies of Time-of-Flight Sensing, and Proximity and Limit Sensing, two essential technologies that enable precision in a wide array of applications from automotive to consumer electronics. We also take a closer look at A2L Sensors, exploring their capabilities and real-world applications, and uncover the potential of Tunnel Magnetoresistance (TMR) Technology, a breakthrough in sensor efficiency. For those involved in chip manufacturing, our feature on Data Acquisition Solutions in Advanced Lithography provides insights into cutting-edge techniques driving semiconductor fabrication forward. Meanwhile, the I3C Communication Protocol article offers an in-depth look at how this technology is revolutionizing IC-to-IC communication, enabling faster and more flexible solutions. We’re also thrilled to include practical resources, such as Arduino Sample Code for SPI Absolute Encoders, making it easier than ever for hobbyists and professionals alike to integrate these technologies into their projects. And for those looking to expand their knowledge, our article on Signal Integrity Fundamentals will help sharpen your understanding of this vital aspect of modern electronics design. Whether you are a seasoned engineer or a curious learner, this issue is packed with valuable insights and practical knowledge to enhance your understanding and keep you at the forefront of these dynamic fields. Thank you for reading, and we hope you find inspiration and innovation on every page.
Precision in a flash with direct time of flight sensing
By Jeff Shepard Contributed by DigiKey’s North American Editors
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A smartphone user frames a shot of their cat crouched in the hallway shadows. Pulses of light travel from the device, bounce off the cat, and return — allowing the phone’s direct time-of-flight (dToF) sensor to precisely measure distance. The phone automatically sharpens its focus, producing a crisp, clear image. This seamless experience, taken for granted by millions of users, is the result of finely tuned optical sensing technology working behind the scenes.
extremely short, we’re talking a few hundred picoseconds.) When this light hits an object and reflects back, the sensor detects it using an array of single photon avalanche diodes (SPADs), which are highly sensitive to even the faintest returning photons. The sensor’s time-to-digital converter (TDC) acts as a stopwatch, measuring the time taken from pulse emission to the received signal. Since the speed of light is a known constant, the distance to the object can be calculated using the formula:
A single pulse isn’t enough to ensure accuracy, so the sensor fires off hundreds of thousands of pulses per measurement cycle. The results are compiled into a histogram and processed by an embedded microcontroller, which determines the distance along with a confidence score based on the signal-to-noise ratio (SNR). This data is transmitted via a simple I²C interface.
But dToF isn’t just advancing smartphone photography. This same technology is making its
Photo Travel Time
Measured Distance =
x Speed of Light
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way into industrial automation and consumer electronics, where devices are increasingly relying on spatial awareness to trigger functions or adapt intelligently to user behavior. Whether it’s a robot vacuum effortlessly dodging furniture and curious pets, or a facial recognition system that wakes up when someone approaches — dToF sensors are enabling intuitive interactions within a broad spectrum of environments. In this article, we will explore the fundamentals of dToF sensing, and how the TMF8806 sensor from ams OSRAM is enhancing ranging solutions.
How dToF sensors work
A dToF sensor operates by emitting an extremely short pulse of infrared light using a vertical cavity surface emitting laser (VCSEL). (By
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Precision in a flash with direct time of flight sensing
Let’s talk about the TMF8806’s power efficiency in a little more detail. The sensor can operate in ultra-low power modes, consuming as little as 14 µA at a 0.5 Hz measurement rate. Even at 30 Hz, power consumption remains at just 27 mA. Because the TMF8806 features extremely fast startup — less than 5 ms — it allows users to switch the device off between measurements. Users can control the duty cycle from their host microcontrollers, which currently operate in sub-microamp modes. In other words, by using the microcontroller to wake up the sensor, take a measurement and go back to sleep, users can achieve highly efficient duty cycles and overall power consumption. The TMF8806 also offers greater design flexibility. It supports multiple optical configurations, including a default mode optimized for minimal cover glass, a large air gap mode allowing up to 20 mm between the sensor and the outer surface, and a thick cover glass mode that supports protective layers up to 3.2 mm thick. This adaptability makes the sensor ideal for industrial applications, where thicker glass and greater mechanical tolerances are common. It is generally recommended to include an optical barrier or isolator between the cover glass and the sensor, as this helps to reduce production tolerances and improve performance.
A sample histogram demonstrating multiple pulses of light. (Image: ams OSRAM.)
While the sensor won’t be fazed by a little dust or smudge on the cover glass, excessive buildup can degrade performance over time. Furthermore, the number of measurements taken per second varies by application. For instance, a video camera autofocus system may require 30 measurements per second, while presence detection in a smart appliance may need only a few per second. Higher measurement rates increase power consumption due to the higher number of VCSEL pulses. Single-zone dToF sensors focus on detecting the closest object within a fixed field of view. Due to their compact nature, single-zone dToF sensors are generally well-suited to systems where space and power is limited.
Introducing the TMF8806 sensor
The TMF8806 from ams OSRAM is a single-zone dToF sensor designed to detect objects from as close as 1 cm to as far as 10 m. Within its tiny footprint of just 2.2 × 3.6 × 1 mm, the device includes a VCSEL emitter, SPAD array, TDC and on-chip histogram processing in one fully integrated module, making it easy to implement in various settings. One of the key improvements in the TMF8806 is its expanded distance sensing capability. The sensor operates in standard 2.5-meter and 5-meter modes without requiring a firmware download, leading to faster startup and more power-efficient operation. A firmware update enables the extended 10-meter range for applications requiring longer-distance sensing.
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result, the sensor achieves excellent resolution and maintains accurate distance measurements within ±5% in both dark and bright conditions.
Conclusion
The TMF8806 represents a step forward in dToF sensing. With built-in 2.5-meter and 5-meter modes that don’t require a firmware download, it streamlines development for engineers looking to add precise ranging to their designs — whether for wake-on-approach interfaces, robotic navigation, or touchless interaction. But the real beauty of the TMF8806 is how it is built to fit into the real world. Its ultra-low power operation makes it a natural choice for low-power systems, while its flexible optical configurations support varying cover glass thicknesses and air gaps. Plus, with support for lower interface voltages, it’s ready to connect with the next generation of high-integration processors. As industries push for smarter, more responsive systems, dToF sensors help bridge the gap between simple detection and intelligent interaction. Whether facilitating precision sensing in an automated warehouse or improving gesture control in consumer electronics, they continue to refine the way machines interact with their environment.
How the histogram distinguishes between detected objects and noise. (Image: ams OSRAM.)
The sensor further has the ability to support a lower interface voltage of 1.2-V I²C, in addition to the higher voltages that other ams OSRAM devices offer. This enables it to connect with a wide range of host processors, such as higher-integration processors that are becoming more widely used. The TMF8806’s parts are rated for operation across a broad temperature range (-40 to 85°C), and support a voltage supply range of up to 3.5 V. The TMF8806 also features improvements in electromagnetic compatibility (EMC), with the ability to enable spread spectrum modes for reducing electrical noise interference. Users can additionally set thresholds for lower and upper limits, where the sensor will only trigger an interrupt or report an object within a preset distance.
The TMF8806 operates with a 940-nm VCSEL, which includes built-in Class 1 eye safety circuitry. This system actively monitors the VCSEL and shuts down the driver if a fault is detected. The device also incorporates sunlight rejection filters to enhance outdoor performance. For applications requiring even stronger sunlight rejection, users can apply additional external filtering on the cover glass to further improve accuracy in bright environments. At the core of the TMF8806 is a high-sensitivity SPAD detection system and a fast TDC architecture,
capable of processing sub- nanosecond light pulses, as
mentioned earlier. It has a high SNR and wide dynamic range. Its built-in crosstalk compensation minimizes false readings from cover glass reflections, and it can reject multipath interference. As a
To learn more, visit TMF8806.
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How low-power overmolded reed switches solve vexing position sensing challenges
By Jeff Shepard Contributed by DigiKey’s North American Editors
Whether you’re designing solutions for automotive, consumer or industrial systems, the space available continues to get smaller. But the challenges, including the needs for low power consumption and high-speed switching of control and position sensing signals, continue to grow. You also need devices that are robust and easy to integrate. Now, you can turn to the new 59177 Series ultra-miniature overmolded reed switches from Littelfuse that deliver solid performance with low power consumption in a space-saving configuration and solve vexing design challenges for level monitoring, position sensing, tamper detection, and similar functions. They are suited for diverse applications like security systems, consumer appliances, metering, process monitoring, and battery-powered devices.
The low profile gives you a new option for solving design challenges in applications that need to switch up to 170 Vdc and up to 0.25 A at 10W, maximum, or 120 Vac and up to 0.18 A, at 10 volt-amperes (VA), maximum. When closed the maximum contact resistance is only 220 mΩ. Quick reaction times are often needed, and the 59177 series delivers. These switches close in a maximum of 0.5 ms (including bounce) and have a release (opening) time of 0.2 ms, maximum, both according to EIA/ NARM RS-421-A. Even though they can quickly switch high power levels, standby and operating power consumption is zero, so is leakage current when the switch is off, you can’t get lower. The 59177 series reed switches can help you maximize the operating time of battery-powered Internet of Things (IoT) designs and meet the most demanding standby power requirements for ac-line operated devices. Robust and reliable These switches are rated for operation from -40 to 125°C. The thermoset over mold material enhances the overall robustness and durability, and the inward formed J-shaped leads contribute to improved mechanical resilience and minimize concerns
Low profile, big performance
The new low-profile design is key. The 59177 series is only 9 mm high, over 20% thinner than the 11.43 mm height of previous reed switches. Overall dimensions of these Form A single-pole single-through normally-open (SPST-NO) switches are 9.0 mm x 2.5 mm x 2.4 mm (0.354”x 0.098‘’x 0.094‘’) with inward formed J-shaped leads that support compact solutions (Figure 1).
Figure 1: From the compact package outline to the lead structure, 59177 series reed switches are designed to solve difficult position sensing challenges. (Image source: Littelfuse)
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How low-power overmolded reed switches solve vexing position sensing challenges
sensing and switching to take place at a relatively large distance and need a higher sensitivity device. Reed switches with lower sensitivities are best suited if the application requires a short activation distance. If the switch is too sensitive, it can experience false triggering from stray magnetic fields or vibrations. If the switch is not sensitive enough, it might not activate when needed. In either case, system reliability suffers. The basic parameter related to sensitivity is ampere-turns (AT) that measure how close a magnet needs to be to trigger a switch. A low AT indicates a higher sensitivity, and the switch will activate with a weaker magnet of over a greater distance. A high AT switch needs a stronger magnet or closer proximity for operation. Littelfuse specifies three parameters related to sensitivity. The pull-in AT range measured before molding and modification of the AT. The activate distance range in mm. The deactivate distance range in mm. The 59177 series offers three sensitivity options denoted by "S", "T", and "U", that correspond with models, 59177-1-S-00-D, 59177-1-T-00-D, and 59177-1-U-00-D, respectively (Table 1).
with thermal expansion.
know that security devices aimed for use in homes can experience high levels of shock and vibration. The 59177 series excel in those applications as well. The compact size and no leakage current when open in standby, plus zero operating power consumption
The overmolded design provides excellent mechanical shock and vibration resistance, making it suitable for applications where the switch may experience mechanical stress. You can design these switches into applications with up to 100 G of shock and 30 G of vibration, as specified in EIA/NARM RS-421-A and MIL-STD-202. The hermetically sealed, magnetically operated contacts ensure reliable operation and protection from the environment. Hermetic sealing also improves switch operation by protecting the contacts from dust and other pollutants that can interfere with the operation of unsealed mechanical or optical switches. Finally, the hermetic sealing makes them suitable for use in explosive atmospheres where even tiny sparks from conventional switches constitute a hazard. The 59177 series is certified to European standard ATEX (ATmosphères EXplosibles) II 3 G Ex nC IIC Gc. The ability to operate in harsh environments makes the 59177 series suitable for a wide range of applications. Of course, the ATEX rating can be needed in industrial settings, but if you’ve ever experienced a door or window slammed shut in a residence, you
of these switches bring huge benefits to battery-powered applications that may never
experience harsh shock or vibration, like tamper protection for meters, proximity and limit sensing in small consumer appliances, and some types of process control equipment. While the general specifications make these reed switches suited for a wide range of applications, the ability to select from several sensitivity levels makes it simple for you to optimize performance
for specific design and packaging requirements.
Sensitivity selection Being able to select the
sensitivity of reed switches is a crucial specification since it determines the activation distance and reliability of the switching action, important considerations to ensure optimal performance based on your specific application demands.
Some applications require
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Table 1: The three sensitivity levels of the 59177 series support AT ratings from 6 to 20 making them suitable for a wide range of application requirements. (Table source: Littelfuse)
addressing vexing position and motion sensing challenges. They can switch up to 10 W, are hermetically sealed against harsh environments, and are mechanically robust. Their zero standby and operating power consumption is perfect for both battery-powered IoT and ac-powered applications. Finally, they’re designed to simplify system integration and support automated assembly.
Alnico-5 magnets are suitable in a wide range of applications and offer a balance of strength and temperature stability. They maintain their magnetic properties even at high temperatures, model 57045- 000 is rated for operation at ambient temperatures up to 105°C, and they are corrosion resistant, making them ideal for use in harsh environments. Conclusion Everything about the Littelfuse 59177 series reed switches simplifies your tasks when
Simple integration Littelfuse 59177 series ultra- miniature reed switches are designed to simplify system integration. They are available in cut tape, tape and reel (complies with EIA-RS-481-1) and Digi- Reel formats to fit your specific assembly needs. They are compatible with pick and place assembly and their ability to operate through non-ferrous materials like wood, plastic, or aluminum, expands application packaging possibilities. They are solder reflow compliant to the IPC-A-610 standard, further ensuring ease of manufacturing and assembly. The companion model 57045- 000 Alnico-5 magnet is in a rectangular 0.700" L x 0.130" W x 0.170" H (17.8 mm x 3.30 mm x 4.32 mm) package with mounting clips to ease installation onto printed circuit boards (Figure 2). The model sensitivities detailed in Table 1 are based on using the 57045-000 magnet.
Figure 2: This 57045-000 Alnico-5 magnet is optimized for use with 59177 series reed switches and clips directly into the circuit board for quick and easy assembly. (Image source: Littelfuse)
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Article Name
How A2L sensors make sure refrigerants don't blow(up)
What HVAC engineers need to know about A2L The HVAC industry is no stranger to design trade-offs. In fact, it is staring down an industry-wide redesign thanks to the adoption — and trade-offs — of A2L refrigerants. Historically, refrigerants have been harsh on the environment. This led to the phaseout of formulations with high ozone depletion potential (ODP). Since the phaseout started in the early 2000s, the UNEP estimates that the ozone layer will fully recover by mid-century. Unfortunately, these replacement refrigerants came with a price — global warming potential (GWP). Even newer refrigerants are now destined to replace those with high GWP, but they also come with a price — flammability. But don’t be alarmed; engineers are designing modifications to HVAC systems, standards, and procedures to ensure everyone’s safe, and the only things that blow are the fans.
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According to newer regulations, the maximum allowable GWP for a refrigerant will be 700. This has led to ASHRAE redefining its refrigerant safety classifications to enable the adoption of A2L refrigerants. This classification previously categorized refrigerants into six buckets defined by: ■ A letter: where A denotes low toxicity and B means highly toxic. ■ A number: where 1 means not flammable, 2 is flammable and 3 denotes highly flammable.
Thus, refrigerants were easily identified to be flammable and/or toxic based on their classifications: A1, A2, A3, B1, B2, or B3. The redefined classification adds a second letter and two more buckets: A2L and B2L. Here, the L denotes that the refrigerant is flammable but with a low burning velocity. A few A2L refrigerants are vying to become the new standard refrigerants in the industry — based on their GWP. The current top contenders are R-32 with a GWP of 675 and R-454B with a GWP of
The history of HVAC refrigerants and their effects on the environment A substance’s impact on global warming is calculated relative to the greenhouse effect of carbon dioxide (CO2). Thus, the GWP of one ton of CO2 is one ton of CO2-equivalent, often shortened to just: 1. The global warming potential of R-410, a popular refrigerant scheduled to be phased down, is 2,088. In other words, the impact of one ton of R-410 released into the atmosphere would be equal to releasing 2,088 tons of CO2.
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How A2L sensors make sure refrigerants don't blow(up)
60335 2-89 standards. For instance, they will need to integrate sensors and control boards that can detect and appropriately respond to a refrigerant leak. Specifically, they will need to add sensors that can sniff out A2L gas and message HVAC control boards so the system can: 1. Shut off the circulation of the refrigerant to stop it from pooling. 2. Shut off all potential ignition sources around the leak. 3. Blow air into where the leak is detected to reduce the chance of ignition. Engineers and technicians working around A2L refrigerants will also need to pay better attention to the tools they use. For instance, any power supply, drill or light source must be labeled A2L compatible if they are to be used in proximity to these refrigerants. Again, all these precautions have remained best practices within the HVAC industry. For instance, any refrigerant leak should be avoided, or quickly detected, to: ■ Maintain maximum efficiency of the HVAC system. ■ Meet OSHA exposure limit regulations. ■ Maintain proper charge, performance, and operations.
467. And though the risks of these refrigerants igniting are minor, engineers must maximize safety by ensuring HVAC systems are equipped with the tools to detect and react to refrigeration leaks. How flammable are we talking? And how engineers must respond. For a refrigerant to be classified as A2L or B2L, it must have a burning velocity lower than 10 cm/s (3.9 in/s). Though these materials will ignite, many tests have shown they tend to self-extinguish. Additionally, the gases must be highly concentrated to ignite as they have a lower flammability level of 300g/ m3 (10.8 lb/in3). Though it’s best to avoid sparks and flames, many A2L refrigerants have been assessed to be safe around some — but not all — common ignition sources. So, A2L refrigerants can and will ignite under various conditions. As a result, many of the ‘best practices’ used around A1 or B1 refrigerants — like purging and evacuating lines — become mandatory when working with A2L or B2L refrigerants. HVAC Engineers working with A2L refrigerants will also need to implement safety equipment into their systems designs as per UL
So, many engineers and technicians will hardly notice a change to their workflows, whereas anyone who took advantage of the ‘timesavers’ available when working with A1 refrigerants must change those habits.
A2L gas sensors and control systems
Engineers need sensors that are capable of detecting A2L refrigerant leaks to ensure the safe transition of the HVAC industry towards these more environmental materials. Fortunately, the HVAC industry is not the first to make this transition; most automotive vehicles already utilize A2L refrigerants. Therefore, HVAC engineers have access to tested equipment and procedures to ensure their future success. For instance, consider Sensirion thermal conductivity CMOSens MEMS chip series ¬— which contains the SGD43S-M3-S5 and SGD43S- M3-S7. They have already been used around the world for automotive and medical sensor applications. The sensor detects A2L gases using thermal conductivity. As a result, it is protected from common sensor issues like contamination, poisoning, drift, and the degradation of mechanical
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components. Sensirion sensors are reported to have a 15-year lifecycle. During that time, the sensor will not need to be recalibrated or rezoned. The SGD43S-M3-S5 and SGD43S-M3-S7 sensors are capable of producing dual contact relay output so they can trigger a signal to a control board. The board can then start a blower, switch off heat sources, and stop the flow of refrigerant within the system. Technicians can also use the LED on the sensor to quickly detect its status. Finally, the sensors meet current industry standards like UL 60355-2-40 and UL 60335-2- 89, so they are ready to use. The main difference between the SGD43S-M3-S5 and SGD43S-M3-S7 is the refrigerants they are calibrated
The Sensirion thermal conductivity CMOSens MEMS chip series, containing the SGD43S-M3-S5 and SGD43S-M3-S7, can detect A2L leaks and ensure the safety of HVAC systems. (Image: Sensirion AG, DigiKey.)
to detect. The S5 model is calibrated for R-454B and R-32, so it is already primed to work with the two leading A2L refrigerants in the HVAC industry. The S7 model, however, is calibrated to detect R-454A, R-454C, and R-455A and is thus more useful in refrigeration applications.
For more information on the SGD43S-M3-S5 and SGD43S- M3-S7 and how they can be integrated into HVAC and refrigeration systems, read this product page on DigiKey.com.
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Advancing magnetic sensing with Allegro MicroSystems’ Tunnel Magnetoresistance (TMR) technology
By Allegro MicroSystems
From the automobiles we drive and the factories that power our economy to the smartphones in our pockets and the medical devices that save lives, magnetic sensors are crucial components used to sense position, speed, and current. However, with the increasing demands of emerging applications, standard magnetic sensors have reached their limits. To achieve greater accuracy, lower power consumption, and improved reliability, an improved type of sensor is required. This article explores the principles of tunnel magnetoresistance, sensors that use this phenomenon, as well as performance benefits over previous magnetic sensing technologies. The evolution of magnetic sensing Hall effect sensors, which have been widely used for decades, operate on the effect discovered by Edwin Hall in 1879, which states that whenever a current-carrying conductor is placed in a magnetic field, it produces a voltage difference that is perpendicular to the current and magnetic field. While hall effect sensors are cost-effective components, their sensitivity is typically limited, making them unsuited for applications that demand high precision and the ability to detect weak magnetic signals.
Anisotropic magnetoresistance (AMR) sensors, another common technology, exploits the anisotropic magnetoresistance effect to achieve higher sensitivity compared to Hall effect types. In AMR sensors, the electrical resistance of a ferromagnetic material varies, based on the angle between the current flow and magnetization direction. While AMR sensors have higher sensitivity compared to Hall effect types, they typically have a lower signal-to-noise ratio (SNR). These sensors can also consume more power than Hall effect sensors, which can limit their suitability for low-power applications. Giant magnetoresistance (GMR) sensors, a more recent development, comprise multiple layers of ferromagnetic materials separated by thin non-magnetic layers. The resistance of this sensor changes significantly when exposed to an external magnetic field, allowing for higher sensitivity and improving the signal-to-noise ratio compared to hall effect and AMR sensors. GMR sensors have been applied in various products, including hard disk drives, automobiles, and biosensors. On the downside, however, depending on the application GMR sensors consume more power and are susceptible to external interfering magnetic fields.
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Advancing magnetic sensing with Allegro MicroSystems’ Tunnel Magnetoresistance (TMR) technology
To overcome the performance limitations of these magnetic sensor solutions, engineers can opt for advanced magnetic technologies like tunnel magnetoresistance (TMR) sensors, which offer higher sensitivities, improved power efficiency, thermal stability, and robustness. How tunnel magnetoresistance (TMR) technology works Tunnel Magnetoresistance technology harnesses principles of quantum mechanics for accurate magnetic sensing. TMR sensors have a magnetic tunnel junction (MTJ) – a nanoscale structure that is composed of dual ferromagnetic layers separated by an ultra-thin insulating barrier. This insulating barrier, typically made of crystalline magnesium oxide (MgO) and a few atomic layers thick, allows electrons to tunnel through it quantum-mechanically. In classical physics, an electron cannot pass through an insulating barrier. However, in quantum mechanics, there is a slight probability that an electron can tunnel through the barrier, even if its energy is lower than the barrier height. This tunneling depends on the relative orientation of the magnetization in the two ferromagnetic layers of the MTJ.
Image credit: Allegro MicroSystems blog
When the magnetizations of the ferromagnetic layers are parallel, the electrons in the majority spin state of one layer can easily tunnel into the majority spin state of the other layer, resulting in a low-resistance state. Conversely, when the magnetizations are anti- parallel, electrons in the majority spin state of one layer must tunnel into the minority spin state of the other, leading to a high resistance. This change in resistance, called the “TMR effect,” is larger than the resistance change in other magnetic sensors, allowing TMR sensors to detect even the weakest magnetic fields precisely. The Magnetoresistance Ratio (MR) quantifies the performance of a TMR sensor by calculating the
percentage change in resistance between the parallel and antiparallel magnetization states. TMR sensors achieve MR ratios of over 200%, significantly higher than those of AMR and GMR sensors, with MR ratios of less than 10% and 20%, respectively. This high MR ratio translates to improved sensitivity, which allows TMR sensors to detect very weak magnetic fields.
Another advantage of TMR and GMR sensors are their compatibility with standard
semiconductor manufacturing processes. The sensors can be fabricated with advanced thin-film deposition techniques, such as sputtering and molecular beam epitaxy, and incorporated with other components on a single
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chip. This compatibility enables manufacturers to design compact, low-power, and cost-effective TMR sensors that are suitable for a broad range of applications. Advantages of TMR over other magnetic sensing technologies TMR sensors exhibit remarkably high sensitivity, with the ability to detect magnetic fields as low as a few microTesla. This high sensitivity is a result of the larger MR ratio achievable in TMR sensors, which can
exceed 200%. In comparison, AMR sensors typically have MR ratios of less than 5%, while giant magnetoresistance (GMR) sensors have MR ratios of around 10-20%. TMR sensors also operate at extremely low power levels, consuming less power compared to AMR and GMR sensors. This low power consumption is due to the high resistance of the MTJ and the low current required for sensing. For example, TMR sensors can utilize supply voltages as low as 1V and consume a small amount of current, making them highly energy efficient. This makes
these sensors useful in battery- powered applications such as wearables and IoT nodes, where extended battery life and low energy footprint are critical. TMR sensors exhibit excellent linearity, meaning that the sensor output is directly proportional to the applied magnetic field over a wide range. This linearity is a result of the well-defined, stable magnetic response of the MTJ, which is governed by the quantum mechanical tunneling process itself. The linear responses of TMR sensors simplify the calibration process and ensure
Image credit: Allegro MicroSystems
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Advancing magnetic sensing with Allegro MicroSystems’ Tunnel Magnetoresistance (TMR) technology
that measurements are accurate, without the need for complex compensation algorithms. In terms of thermal stability, TMR sensors offer a stable performance over a broad temperature range, typically from -40°C to 150°C. The stable performance of these sensors ensures reliable operation
measurements. These sensors leverage the inherent benefits of TMR technology, such as higher sensitivity, low power consumption, wide dynamic range, and industry-leading performance over a temperature range from -40°C to 150°C. XtremeSense Crocus Technology TMR sensors incorporate sophisticated signal conditioning and digital processing (DSP) capabilities to improve sensor performance and ease of use. Signal conditioning circuits, such as low-noise amplifiers and filters, amplify and process the sensor output to reduce SNR and minimize the effect of external noise. These circuits have been carefully designed to match the characteristics of the TMR sensor, ensuring optimal performance and signal integrity. Allegro TMR technology uses differential sensing to reject stray fields, this ensures stable and reliable sensor performance in a broad range of operating conditions. This technology is crucial in applications where sensors are exposed to strong magnetic fields or where multiple sensors will be placed in close proximity, as it prevents crosstalk and interference. In addition to EMI shielding, Allegro’s unique packaging allows for multiple sensors and
signal conditioning circuitry to be built into a single package. This integration simplifies system design, reduces the overall footprint, and improves signal integrity. By combining the TMR sensor with advanced signal conditioning and processing circuitry, XtremeSense sensors minimize the need for external components and reduce the design complexity for engineers. TMR also includes digital interfaces, such as I2C and SPI, which allows them to be integrated with microcontrollers, digital signal processors, and other digital systems for easy configuration, control and data readout from sensors. These interfaces have advanced features like programmable gain settings, filtering options, and self-calibration, offering designers greater flexibility and control over sensor performance. Key applications In the automotive sector, TMR sensors are instrumental in enabling advanced driver assistance systems (ADAS) to enhance vehicle safety and performance. For example, these sensors can be used for position sensing in electric power steering systems, providing accurate feedback on steering
in harsh environments, such as automotive and industrial
applications, where sensors can be exposed to extreme temperatures and temperature fluctuations.
Product highlight: Allegro MicroSystems’
XtremeSense TMR sensors Lastly, TMR sensors are inherently robust and reliable, with a solid- state design that eliminates moving parts and reduces the risk of mechanical failure. For example, the MTJ structure itself is resistant to mechanical stress, vibration, and shock. TMR sensors also demonstrate resistance to radio frequency interference, making them suitable for noisy electrical environments. Allegro MicroSystems’ XtremeSense TMR portfolio includes a wide range of sensors optimized for various applications ranging from position sensing to high-bandwidth current
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Image credit: Allegro MicroSystems
angle and enabling smooth and responsive steering control. Other applications include pedal position detection for accurate throttle and brake control and transmission gear selection. This technology can also be used in motor control and battery management to provide current measurements to optimize the performance of motors and ensure efficient charging and discharging of vehicle batteries. In industrial applications, TMR sensors can provide accurate position feedback in servo motors and linear actuators for motion control and positioning in manufacturing systems, pick- and-place machines, and other
automated equipment. Current sensing is also essential for industrial applications for motor protection, power monitoring, and energy management. Here, TMR sensors can provide precise current measurements for real-time monitoring of motor health, detection of overload conditions, and optimizing energy consumption. TMR sensors can also be integrated into consumer products like gaming devices and smartphones to provide new features and enhanced user experiences. For example, these sensors can provide gesture recognition allowing users to interact with devices
through intuitive motion controls. Other applications include motion tracking and orientation detection for more immersive
gaming experiences and advanced user interfaces.
Conclusion TMR technology is a breakthrough in magnetic sensing that offers better performance, energy efficiency, and reliability compared to standard magnetic sensors. With their high sensitivity, low power consumption, temperature stability, and wide dynamic range, these sensors are able to meet the current and future needs of various industrial, automotive, and consumer applications.
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retroelectro
This is a map of Europe as it was when the galvanometer was invented.
An illustration the test tool that Ampere devised when investigating electromagnetism.
Experiments on the effect of a current of electricity on the magnetic needle
By David Ray Cyber City Circuits
Galvani's experiments ignited a sensation across Europe, capturing public imagination and fueling intense scientific curiosity. His work prompted Alessandro Volta to create the first ‘reliable’ electric battery (the voltaic pile), which in turn enabled Hans Christian Ørsted, André-Marie Ampère, and Georg Simon Ohm to perform groundbreaking experiments that fundamentally reshaped human understanding of electricity. The story that led to the galvanometer is part of a much larger story that shows how connected Europe was. From 1820 through the end of the nineteenth century, the rapid pace of discovery and invention rivaled the semiconductor boom in the latter half of the twentieth century.
This chain reaction of discoveries led directly to the development of the galvanometer, an instrument initially intended simply to detect and measure small electrical currents but soon found indispensable applications in fields as diverse as medicine, telegraphy, and physics. The birth of the Modern Age The late 1700s was a significant turning point for society. Even the ancient Greeks knew about electricity, but nobody knew what it was or where it came from. By then, people were able to generate electricity by using giant spinning contraptions that would rub small leather cushions onto large glass globes. The faster the ‘electrical machine’ spun, the more electricity
The Galvanometer At the turn of the nineteenth century, electricity was still a mysterious force—poorly understood, difficult to measure, and often viewed with wonder or suspicion. Scientists exploring electricity needed precise instruments capable of detecting even the faintest currents, laying the groundwork for the invention of a device that would revolutionize both scientific study and industrial development: the galvanometer. The name 'galvanometer' is rooted in the intriguing experiments of Luigi Galvani, an Italian physician and physicist who, in the late 18th century, famously observed the twitching of frog legs when subjected to electrical current— what he termed "animal electricity."
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it produced. Sometimes, these machines produced so much high- voltage current that they fatally electrocuted onlookers. In 1745, the elegant invention of the Leyden jar was introduced, giving the world a way to actually store electricity. Before, any charge from the machines would quickly dissipate. Now that a charge could be stored, it could be studied. The field would stagnate until Benjamin Franklin’s 1752 kite experiment turned many doctors, mechanics, and natural philosophers into hobbyist electrical engineers. Newspapers around the world published detailed instructions on how to construct a kite from two cedar sticks and a silk handkerchief. There are accounts of hundreds of people successfully recreating the experiment within months of Franklin publishing it.
‘Using complex machines that spin glass and can generate thousands of volts of electricity was the best method for studying electricity.’
Franklin’s experiments resulted in the practical use of the lightning rod, which not only made people safer but also allowed both amateurs and professionals to study electricity easier when combined with large Leyden jars.
In 1800, Alessandro Volta invented the voltaic pile. This device was simple: alternating discs of two different metals, typically copper and zinc, separated by layers of cloth or paper soaked in saltwater or acid, which acted as an
Retro Electro Fun Fact: The Leyden Jar was independently invented by Pieter van Musschenbroek in Leiden, Netherlands. It could store an electrical charge in a way similar to a capacitor, with dual conductors, and a dielectric in the form of a glass jar. The jar was filled with water or brine and sometimes beer. Not at all understanding what he had made, Musschenbroek thought the electrical fluid (effluvia) was being injected and stored within the water which was later omitted altogether. Learn more about electrical effluvia in the Retro Electro article ‘Electricity or Ethereal Fire.’ (Link: https://emedia.digikey.com/view/785457150/28-29/)
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Italian doctor Luigi Galvani found that you can connect a Leyden jar to dead animals and make them jump around. Traveling doctors were roaming rural New England, treating everything from asthma to dysentery with electric shock. Humphrey Davy was about to isolate several elements (calcium, magnesium, potassium, sodium) for the first time with electrolysis. …and in the Netherlands, Hans
electrolyte. Stacked in layers, this arrangement produced a stable, continuous electric current, unlike earlier electrostatic machines or Leyden jars, which could only deliver brief bursts of electricity and could never provide any consistency.
Christian Ørsted started his investigation of electricity.
Hans Christian Ørsted
Ørsted was a brilliant mind. He grew up on an island off the coast of Denmark called Langeland. There was no formal school, but community members would take time to teach children arithmetic, drawing, and languages like German and French from people like the town’s mayor. He attended the University of Copenhagen and received a PhD in 1799. Soon after the invention of the voltaic pile was published, he began conducting his own experiments as a young man. He spent a few years traveling Europe to study with other researchers. At the time, people suspected a connection between magnetism and electricity, but nobody could find it. It sounds simple today, but researchers
Hans Christian Ørsted
would put a compass needle near batteries, Leyden jars, and high- voltage wires, and the connection could not be made. While teaching a class and demonstrating that a wire will produce heat when connected to a battery, he noticed that a nearby compass fluttered when the battery was connected. After meticulous experimentation,
Benjamin Franklin’s kite experiment really gave the field of study a kick start in the 1750s
The period between the late 1700s and 1820 was ripe for discovery in electricity. Finally, an experimenter could have a constant and reliable source of electricity. For the most part, few among the many experimenters had any idea what they were doing. There are stories of people tying lightning rods to elephants and other large animals.
all he could come up with was that there was a clear
connection between electricity and magnetism when a very high current was run through a wire. He found that a compass needle will deflect perpendicular to the conductor, demonstrating that the
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magnetic field the coil generates travels around the wire and not through it, like everyone assumed. The problem now is that nobody knew how to describe this observation in practical mathematical terms. Ørsted
experimented for months and then published a short paper in Latin titled ‘Experiments on the Effect of a Current of Electricity on the Magnetic Needle.’ Papers like this took some time to travel and get translated through Europe.
Writer’s Note: While researching, the writer found numerous references to gossip and experiments concerning the connection between electricity and magnetism. It appears that the wire and compass experiment had been conducted
for decades before Ørsted’s discovery. The writer hasn’t found what made those experiments
unsuccessful. An Italian researcher named Gian Domenico Romagnosi published a study on the connection between static buildup and the movement of a compass needle in 1802, but it seems that his research didn’t disseminate widely across Europe.
In the spring of 1820, during a lecture, Ørsted discovered evidence linking magnetism to electricity.
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created by current in a wire could be ‘multiplied’ by coiling the wire. He coiled wire around a wooden rectangular frame and placed a compass needle in the center. By the fall of 1820 (just months after Ørsted’s paper appeared), Schweigger constructed his ‘Multiplier Galvanometer,’ also called ‘Schweigger’s Multiplier.’ In September of 1820, Schweigger presented his findings at the University of Halle (where he was also a teacher). Soon after, his paper was published in the German Literary Gazette, eventually showing up on the desk of every academic physics researcher in Europe.
This image illustrates the simple demonstration performed by Ørsted that initiated the modern age.
As the discovery traveled Europe…
In Bavaria…
In the Summer of 1820, Johann Schweigger was sitting at his desk when the Dutch journal that first published Ørsted’s discovery came in the post. Schweigger was the editor and publisher of the German scientific journal ‘ Journal für Chemie und Physik ’ (often known simply as ‘Schweigger's Journal’). He was uniquely positioned to be one of the first in the world to learn about new scientific discoveries. Recognizing the significance of Ørsted’s experiment, Schweigger immediately saw the potential to measure electric currents with precision. Schweigger first determined that the fields
Johann Salomo Christoph Schweigger
This is a depiction of the Schweigger Multiplier.
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In France…
chronic depression. While a genius, he could only ‘work at 100 MPH’ or not at all. When Ampère learned of Ørsted’s discovery, he immediately set out to investigate in hopes of mathematically explaining this new connection between electricity and magnetism. Remember, that the connection was suspected by many, but nobody had reproducible evidence of such a connection until now. Within a week, Ampère conducted a series of experiments and presented his initial report to the French Academy of Sciences just days after Arago published the discovery.
Ampère discovered that two parallel wires carrying electric currents either attract or repel each other, depending on the direction of the current. This critical finding demonstrated that electricity creates magnetic effects not only on compass needles but also directly between wires. Ampère introduced the first detailed mathematical proof of electromagnetism, now known as Ampère’s Law. It states that ‘the magnetic field created by an electric current is proportional to the size of that electric current with a constant of proportionality equal to the permeability of free space (air).’ For the first time that story and more in the Retro Electro article ‘Genius and Tragedy.’ (Link: https:// emedia.digikey.com/ view/687420822/38/) Retro Electro Sad Fact: Did you know that French revolutionaries beheaded Ampère’s father while Ampère was a teenager? Read
A French physicist named Francois Arago found a copy of Ørsted’s paper while visiting Geneva and brought it back to Paris to be published in the French scientific journal Annales de Chimie et de Physique . In September 1820, he demonstrated the experiments to an audience in Paris, including the mathematician and chemist André-Marie Ampère.
François Arago
Excited by the challenge of explaining the movement of the needle, Ampère dedicated his energy to solving it. Already a highly distinguished mathematician, chemist, and philosopher, he pursued problems that captivated him. He struggled with severe and
André-Marie Ampère’
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