Monthly Archives: March 2024

What are Olfactory Sensors?

We depend on our five senses to help us understand the world around us. Each of the five senses—touch, sight, smell, hearing, and taste—contributes individual information to our brains, which then combines them to create a better understanding of our environment.

Today, with the help of technology like ML, or machine learning, and AI, or Artificial Intelligence, we can make complex decisions with ease. ML and AI also empower machines to better understand their surroundings. Equipping them with sensors only augments their information-gathering capabilities.

So far, most sensory devices, like proximity and light-based ones, remain limited as they need clear physical contact or line of sight to function correctly. However, with today’s technology trending towards higher complexity, it is difficult to rely solely on simple sensing technology.

Olfaction, or the sense of smell, functions by chemically analyzing low concentrations of molecules suspended in the air. The biological nose has receptors for this activity, which, on encountering these molecules, transmit signals to the parts of the brain that are responsible for the detection of smell. A higher concentration of receptors means higher olfaction sensitivity, and this varies between species. For instance, compared to the human nose, a dog’s nose is far more sensitive, allowing a dog to identify chemical compounds that humans cannot notice.

Humans have recognized this superior olfactory ability in dogs and put it to various tasks. One advantage of olfaction over that of sight is the former does not rely on line-of-sight for detection. It is possible to detect odors from unseen objects, which may be obscured, hidden from sight, or simply not visible. That means the olfactory sensor technology can work without requiring invasive procedures. That makes olfactory sensors ideally suited for a range of applications.

With advanced technology, scientists have developed artificial smell sensors to mimic this extraordinary natural ability. The sensors can analyze chemical signatures in the air, and thereby unlock newer levels of safety, efficiency, and early detection in places like the doctor’s office, factory floors, and airports.

The healthcare industry holds the most exciting applications for olfactory sensors. This is because medical technology depends on early diagnosis to provide the most effective clinical outcomes to patients. Conditions like diabetes and cancer cause detectable olfactory changes in the body’s chemistry. Using olfactory sensors to detect the changes in body odor, with their non-invasive nature, provides a critical early diagnosis that can significantly improve the chances of effective treatment and recovery.

The industry is also adopting olfactory sensors. Industrial processes often produce hazardous byproducts. With olfactory sensors around, it is easy to monitor chemical conditions in the air and highlight the buildup of harmful gases that can be dangerous beyond a certain level.

As the sense of smell does not require physical contact, it is ideal for detection in large spaces. For instance, olfactory sensors are ideal for airport security, where they can collect information about passengers and their belongings as they pass by. All they need is a database of chemical signatures along with processing power to analyze many samples in real-time.

High-Voltage TVS Diodes as IGBT Active Clamp

Most high-voltage applications like power inverters, modern electric vehicles, and industrial control systems use IGBTs or Insulated Gate Bipolar Transistors, as they offer high-efficiency switching. However, as power densities are constantly on the rise in today’s electronics, the systems are subjected to greater demands. This necessitates newer methods of control. Littelfuse has developed new TVS diodes as an excellent choice to protect circuits against overvoltages when IGBTs turn off.

Most electronic modules and converter circuits contain parasitic inductances that are practically impossible to eliminate. Moreover, it is not possible to ignore their influence on the system’s behavior. While commuting, the current changes as the IGBT turns off. This produces a high voltage overshoot at its collector terminal.

The turn-off gate resistance of the IGBT, in principle, affects the speed of commutation and the turn-off voltage. Engineers typically use this technique for lower power level handling. However, they must match the turn-off gate resistance for overload conditions, short circuits, and for a temporary increase in the link circuit voltage. In regular operation, the generation of the overshoot voltage typically increases the switching losses and turn-off delays in the IGBTs, reducing the usability and or efficiency of the module. Therefore, high-power modules cannot use this simple technique.

The above problem has led to the development of a two-stage turn-off, with slow turn-off and soft-switch-off driver circuits, which operate with a gate resistance that can be reversed. In regular operations, the IGBT is turned off with the help of a gate resistor of low ohmic value, as this minimizes the switching losses. For handing surge currents or short circuits, this is changed to a high ohmic gate resistor. However, this also means that normal and fault conditions must be detected reliably.

Traditionally, the practice is to use an active clamp diode to protect the semiconductor during the event of a transient overload. The high voltage causes a current flow through the diode until the voltage transient dissipates. This also means the clamping diode is never subjected to recurrent pulses during operation. The IGBT and its driver power limit the problem of repetitive operation, both absorbing the excess energy. The use of an active clamp means the collector potential is directly fed back to the gate of the IGBT vial an element with an avalanche characteristic.

The clamping element forms the feedback branch. Typically, this is made up of a series of TVS or Transient Voltage Suppression diodes. When the collector-emitter voltage of the IGBT exceeds the approximate breakdown voltage of the clamping diode, it causes a current flow via the feedback to the gate of the IGBT. This raises the potential of the IGBT, reducing the rate of change of current at the collector, and stabilizing the condition. The design of the clamping diode then determines the voltage across the IGBT.

As the IGBT operates in the active range of its output characteristics, the energy stored in the stray inductance of the IGBT is converted to heat. The clamping process goes on until the stray inductance is demagnetized. Therefore, several low-voltage TVS diodes in series or a single TVS diode rated for high voltage are capable of providing the active clamping solution.

E-Fuse Future Power Protection

High-voltage eMobility applications are on the rise. Traditionally, fuses are non-re-settable, and sometimes mechanical relays or contactors are used. However, that is now changing. Semiconductor-based re-settable fuses or eFuses are now replacing traditional fuses.

These innovative eFuses represent a significant trend in safeguarding hardware and users in high-voltage and high-power scenarios. Vishay has announced a reference design for an eFuse that can handle high power loads. They have equipped the new eFuse with SIC MOSFETs and a VOA300 optocoupler. The combination can handle up to 40 kW of continuous power load. The design is capable of operating at full power with minimal losses of lower than 30 W without active cooling. The eFuse incorporates important essential features like continuous current monitoring, a preload function, and rapid overcurrent protection.

Vishay has designed the eFuse to manage the safe connection and disconnection of a high-voltage power source. For instance, the eFuse can safely connect or disconnect various vehicle loads safely to and from a high-energy battery pack. The eFuse uses SIC MOSFETS as its primary switches, and these are capable of continuous operation up to 100 Amperes. The user can predefine a current limit. When the current exceeds this limit, the eFuse disconnects the load rapidly from the power source, safeguarding the user and the power source or battery pack. In addition, the presence of a short circuit or an excessive load capacitance during power-up causes the eFuse to initiate an immediate shutdown.

The basic design of the eFuse is in the form of a four-layer, double-sided PCB or printed circuit board of 150 mm x 90 mm. Each layer has thick copper of 70 µm thickness, as against 35 µm for regular PCBs. The board has some connectors extending beyond its edges. The top side of the PCB has all the high-voltage circuitry, control buttons, status LEDs, multiple test points, and connectors. The PCB’s bottom side has the low-voltage control circuitry. It is also possible to control the eFuse remotely via a web browser.

To ensure safety, the user must enable the low-voltage power supply in the first place. They can follow this up by enabling the high-voltage power supply on the input. For input voltages exceeding 50 V, an LED indicator lights up on the board. Vishay has added two sets of six SIC MOSFETS with three connected in parallel in a back-to-back configuration. This ensures the eFuse can handle current flow in both directions. A current-sensing shunt resistor, Vishay WSLP3921, monitors the current flowing to the load. Vishay has positioned the current sensing shunt resistor strategically between the two parallel sets of MOSFETs.

Vishay has incorporated convenient control options in the eFuse. Users can operate the control options via the push buttons on the PCB, or by using the external controller, Vishay MessWeb. Either way unlocks access to an expanded array of features. Alternately, the user can integrate the eFuse seamlessly into a CAN bus-based system. They can do this by using an additional chipset in conjunction with the MessWEB controller. Vishay claims to have successfully tested its reference eFuse design.

IoT Sensor Design

Individuals are progressively integrating electrical components into nearly every system possible, thereby imbibing these systems with a degree of intelligence. Nevertheless, to meet the intelligence requirements posed by diverse business applications, especially in healthcare, consumer settings, industrial sectors, and within building environments, there is a growing necessity to incorporate a multitude of sensors.

These sensors now have a common name—IoT or Internet of Things sensors. Typically, these must be of a diverse variety, especially if they are to minimize errors and enhance insights. As sensors gather data through sensor fusion, users build ML or Machine Learning algorithms and AI or Artificial Intelligence around sensor fusion concepts. They do this for many modern applications, which include advanced driver safety and autonomous driving, industrial and worker safety, security, and audience insights.

Other capabilities are also emerging. These include TSN or time-sensitive networking, with high-reliability, low-latency, and network determinism features. These are evident in the latest wireless communication devices conforming to modern standards for Wi-Fi and 5G. To implement these capabilities, it is necessary that sensor modules have ultra-low latency at high Throughput. Without reliable sensor data, it is practically impossible to implement these features.

Turning any sensor into an IoT sensor requires effectively digitizing its output while deploying the sensor alongside communication hardware and placing the combination in a location suitable for gathering useful data. This is the typical use case for sensors in an industrial location, suitable for radar, proximity sensors, and load sensors. In fact, sensors are now tracking assets like autonomous mobile robots working in facilities.

IoT system developers and sensor integrators are under increasing pressure to reduce integration errors through additional processing circuits. Another growing concern is sensor latency. Users are demanding high-resolution data accurate to 100s of nanoseconds, especially in proximity sensor technologies following the high growth of autonomous vehicles and automated robotics.

Such new factors are leading to additional considerations in IoT sensor design. Two key trends in the design of sensors are footprint reduction and enhancing their fusion capabilities. As a result, designers are integrating multiple sensors within a single chip. This is a shift towards a new technology known as SoC or system-on-chip.

Manufacturers are also using MEMS technology for fabricating sensors for position and inertial measurements such as those that gyroscopes and accelerometers use. Although the MEMS technology has the advantage of fabrication in a semiconductor process alongside digital circuits, there are sensors where this technology is not viable.

Magnetic sensors, high-frequency sensors, and others need to use ferromagnetic materials, metastructures, or other exotic semiconductors. Manufacturers are investing substantially towards the development of these sensor technologies using SiP or system-in-package modules with 2D or 2.5D structures, to optimize them for use in constrained spaces and to integrate them to reduce delays.

Considerations for modern sensor design also include efforts to reduce intrinsic errors that affect many sensor types like piezoelectric sensors. Such sensors are often prone to RF interference, magnetic interference, electrical interference, oscillations, vibration, and shock. Designers mitigate the effect of intrinsic errors through additional processing like averaging and windowing.

The above trends are only the tip of the iceberg. There are many other factors influencing the growing sensor design complexity and the need to accommodate better features.