Wireless device makes magnetism appear in non-magnetic materials

Researchers have succeeded in bringing wireless technology to the fundamental level of magnetic devices. The emergence and control of magnetic properties in cobalt nitride layers (initially non-magnetic) by voltage, without connecting the sample to electrical wiring, represents a paradigm shift that can facilitate the creation of magnetic nanorobots for biomedicine and computing systems where basic information management processes do not require wiring.

New research finds stress and strain changes metal electronic structure

New research shows that the electronic structure of metals can strongly affect their mechanical properties.

Controlling waves in magnets with superconductors for the first time

Quantum physicists have shown that it's possible to control and manipulate spin waves on a chip using superconductors for the first time. These tiny waves in magnets may offer an alternative to electronics in the future, interesting for energy-efficient information technology or connecting pieces in a quantum computer, for example. The breakthrough primarily gives physicists new insight into the interaction between magnets and superconductors.

A superatomic semiconductor sets a speed record

The search is on for better semiconductors. A team of chemists describes the fastest and most efficient semiconductor yet: a superatomic material called Re6Se8Cl2. 

Using sound to test devices, control qubits

Researchers have developed a system that uses atomic vacancies in silicon carbide to measure the stability and quality of acoustic resonators. What's more, these vacancies could also be used for acoustically-controlled quantum information processing, providing a new way to manipulate quantum states embedded in this commonly-used material. 

Cathode active materials for lithium-ion batteries could be produced at low temperatures

Layered lithium cobalt oxide, a key component of lithium-ion batteries, has been synthesized at temperatures as low as 300°C and durations as short as 30 minutes.

Researchers demonstrate a high-speed electrical readout method for graphene nanodevices

Graphene is often referred to as a wonder material for its advantageous qualities. But its application in quantum computers, while promising, is stymied by the challenge of getting accurate measurements of quantum bit states with existing techniques. Now, researchers have developed design guidelines that enable radio-frequency reflectometry to achieve high-speed electrical readouts of graphene nanodevices. 

From square to cube: Hardware processing for AI goes 3D, boosting processing power

A breakthrough development in photonic-electronic hardware could significantly boost processing power for AI and machine learning applications. The approach uses multiple radio frequencies to encode data, enabling multiple calculations to be carried out in parallel. The method shows promise for outperforming state-of-the-art electronic processors, with further enhancements possible.

Electrical control of quantum phenomenon could improve future electronic devices

A new electrical method to conveniently change the direction of electron flow in some quantum materials could have implications for the development of next-generation electronic devices and quantum computers. A team of researchers has developed and demonstrated the method in materials that exhibit the quantum anomalous Hall (QAH) effect -- a phenomenon in which the flow of electrons along the edge of a material does not lose energy.

From a five-layer graphene sandwich, a rare electronic state emerges

When stacked in five layers in a rhombohedral pattern, graphene takes on a rare 'multiferroic' state, exhibiting both unconventional magnetism and an exotic electronic behavior known as ferro-valleytricity.

Revolutionizing energy storage: Metal nanoclusters for stable lithium--sulfur batteries

Lithium–sulfur batteries (LSBs) offer a higher energy storage potential. However, issues like formation of lithium polysulfides and lithium dendrites lead to capacity loss and raise safety concerns. Now, researchers have developed a graphene separator embedded with platinum-doped gold nanoclusters, which enhance lithium-ion transport and facilitate redox reactions. This breakthrough addresses the long-standing issues associated with LSBs, setting the stage for their commercialization.

Magnetoelectric material can reconnect severed nerves

Neuroengineers designed the first self-rectifying magnetoelectric material and showed it can not only precisely stimulate neurons remotely but also reconnect a broken sciatic nerve in a rat model.

Wireless, battery-free electronic 'stickers' gauge forces between touching objects

Engineers developed electronic 'stickers' that measure the force exerted by one object upon another. The force stickers are wireless, run without batteries and fit in tight spaces, making them versatile for a wide range of applications, from surgical robots to smart implants and inventory tracking.

Bipolar Junction Transistor – A Getting Started Guide for Beginners

The Bipolar Junction Transistor (BJT) is one of the two most used types of transistors. You can use it to create audio amplifiers, switch on/off DC lamps, motors, and much more.

In this tutorial aimed at beginners, you’ll learn the basics you need to start having fun and design your own transistor circuits.

Introduction to Bipolar Junction Transistors

The Bipolar Junction Transistor (BJT) is a device made of three layers of semiconductor material; these layers can be either P-type or N-type. The pins of a BJT are named base, collector, and emitter. Each pin is connected to one of these layers.

There are two different types of BJTs known as PNP and NPN. They are named after the arrangement of the semiconductor layers. You can see the construction and symbols of PNP and NPN transistors below.

How the Bipolar Junction Transistor Works

The BJT has two operation modes. It can be used as:

• an amplifier, which means that it can magnify an input signal (for example audio)
• a switch that can turn things (motors, lights, etc) on or off

But, how can you select between one behavior and the other? It all depends on the current that flows through the base. So to be able to design transistor circuits, you need to start by learning how currents flow in a bipolar transistor.

A BJT is controlled by current. For an NPN transistor, a small current flowing into the base turns the transistor ON so that a bigger current can flow from collector to emitter.

β is the gain of your transistor that tells you how much bigger than the base current the collector current is.

This value is given by the manufacturer, and it’s also known as h_FE. You’ll find it in the datasheet of the transistor.

The path from base to emitter works like a diode with a forward voltage of about 0.7V.

The emitter current (I_E) equals the sum of the base current (I_B) and the collector current (I_C). This makes sense since the base and collector currents flow into the transistor, and there is nowhere else for the currents to flow than out from the emitter.

So you have:

The PNP transistor works the same way, just that the currents flow the opposite way.

Basic BJT Configurations

There are essentially three ways to connect a BJT in a circuit, and they are named based on which terminal serves as a common connection point for the input and the output. The three configurations are:

• Common-Emitter Configuration (The most common)
• Common-Collector Configuration (Mostly used for creating a buffer)
• Common-Base Configuration (Not that common)

Common Emitter

The common-emitter configuration is the most common way to connect a transistor circuit. It’s used both to connect the transistor as a switch and to use it as an amplifier. This setup is great for amplifying a tiny voltage or current into a much higher voltage on the output.

In the circuit below an NPN transistor is set up as a common emitter. Its base is connected to the input voltage via a resistor R_B.

To simplify, the input voltage V_BB is represented as a battery. But this is normally a signal such as an audio signal or a microcontroller output pin.

The collector is connected to the DC power source V_CC through a resistor R_L. R_L can either be something you want to control (like a motor or a speaker), or it can be a resistor set to get a specific output voltage range from the collector terminal.

The emitter is connected to the negative terminals of both power supplies, hence the name common emitter.

Common Emitter Calculations

When you design a transistor circuit, you usually want to design it so that you have a specific current flowing through the load R_L. For example, if R_L is a motor, you want to make sure the motor gets enough current to turn on.

The current that flows through R_L is the same as the collector current (I_C) and you can find it from the value of I_B with the following formula as discussed above:

To find the base current (I_B), you need to find the current that flows through R_B. You can find it from the input voltage (V_BB) using the following formula:

V_BE is always around 0.7V (given that the input voltage is high enough). So by adjusting the value of R_B, you can set the base current, and thereby the collector current, to the value that you need.

Common Collector

The common-collector configuration is often used to create a voltage follower or buffer. The output voltage is the same as the input voltage minus 0.7V.

A buffer is useful if you have a signal source that can’t provide enough current for your load. With this circuit, it’s the transistor you choose that determines the maximum current, not the signal source.

Common Collector

When the transistor is turned on, the voltage drop from the base to the emitter is ~0.7V. So when you connect a bipolar-junction transistor in the common-collector configuration, you know that the output is always 0.7V lower than the input. So the output voltage follows the input voltage.

Common Base

The common-base configuration isn’t very common when building circuits with discrete components. However, it’s popular in integrated circuits and RF amplifiers for high frequency. You can learn more about the common-base configuration and how to set it up from this page.

Note: The operating principle for both PNP and NPN transistor types is identical; the only distinction lies in their biasing and the polarity of the power supply for each type.

Operating Regions of a Bipolar Junction Transistor

A transistor can be fully on, fully off, or somewhere in between. These are the operating regions of the bipolar junction transistor.

• Saturation Region (Transistor is turned fully ON)
• Cut-off Region (Transistor is turned OFF)
• Active Region (Transistor is somewhere between fully ON and OFF)

You can set your transistor into each of these regions by controlling the base current (I_B):

If there is no base current, the transistor is off, so it’s in the cut-off region. As you start to increase the base current, the transistor goes into the active region, where it’s partially on. At some point, when the base current is high enough, the transistor goes into the saturation region where it turns fully on.

If you want to use the transistor as a switch, you want to have the transistor in the Cut-off region (open switch) or the Saturation region (closed switch).

If you want to use the transistor as an amplifier, it is the Active region you want to be in. In the active region, the collector current can be found from the base current and the gain (β):

The BJT Transistor as a Switch

To use a bipolar junction transistor as a switch, use the common emitter configuration:

• Emitter: Connected to the ground (0V reference).
• Collector: Connected to the load (e.g., a lamp).
• Base: Connected to the control signal (e.g., push button, microcontroller).
• Load: Connected between the collector and the supply voltage.

Switch Off (Cut-off Region)

To turn the switch off, you need to set the base current to zero which puts the transistor into its cut-off region. So you have:

• No Base current (I_B = 0)
• Base-Emitter voltage V_BE < 0.7v
• No Collector current ( I_C = 0 )
• V_CE = V_CC
• The transistor operates as an open switch

Switch On (Saturation Region)

To turn the switch on, you need to have enough base current to place the transistor into the saturation region. So you have:

• Enough base current to place the transistor into saturation
• Base-Emitter voltage V_BE > 0.7v
• V_CE = 0 (ideally)
• Maximum collector current (I_C = V_CC/R_LOAD)
• The transistor operates as a closed switch

Bipolar Junction Transistor as an Amplifier

If you want to use the BJT as an amplifier, the most common configuration is the common emitter.

Below is a simple amplifier circuit that drives a speaker. The voltage on the input decides the base current. So the higher the voltage, the higher the current.

A very simple audio amplifier

The collector current (which is the same current that goes through the speaker) is limited to the gain of the transistor multiplied by the base current. The base current will vary with the input voltage, which means the collector current will also vary with the input voltage.

So a varying input voltage makes the current in the speaker vary, which creates sound.

To start having current flowing through the speaker in the above example, the input voltage must be around 0.7V as a minimum, since that’s the point where the transistor turns on. If the input voltage is below this, the transistor will be off.

And you can’t increase the current through the speaker more than what is dictated by V_CC and the speaker resistance (I_C(MAX) = V_CC/R_LOAD). So there is a certain voltage on the input that will be the max, and increasing it more won’t make a difference.

So you have a minimum and a maximum input voltage.

But what if the signal you want to amplify does not match that range?

This is where biasing comes in.

BJT Amplifier Biasing

By adding resistors, you can make sure your amplifier accepts a different range of input signals to match whatever you want to amplify. In technical terms, you are biasing the transistor to work in the active region.

Example BJT Amplifier Circuit with Biasing

R1 and R2 divide the V_CC voltage and set the bias voltage for the base so that the transistor is in the active region. C1 and C3 are coupling capacitors whose role is to block the DC components and only allow the AC signal through.

When the transistor is in the active region, it means its collector current is controlled by the base current. The base current is controlled by the input signal, so this means the output signal becomes an amplified version of the input signal.

The resistor R_E and capacitor C2 are there to help bias the circuit properly together with R1 and R2.

Want to learn more about transistor biasing and how to choose the different values? Check out Single Transistor Amplifier Stages by Analog Devices. Or the book Transistor Circuit Techniques, Discrete and Integrated by G.J.Ritchie.

Questions?

Do you have any questions or any feedback you want to share? Let me know in the comment field below!

Copyright Build Electronic Circuits

Twisted science: New quantum ruler to explore exotic matter

Researchers have developed a 'quantum ruler' to measure and explore the strange properties of multilayered sheets of graphene, a form of carbon. The work may also lead to a new, miniaturized standard for electrical resistance that could calibrate electronic devices directly on the factory floor, eliminating the need to send them to an off-site standards laboratory.   

Successful morphing of inorganic perovskites without damaging their functional properties

A research team has successfully morphed all-inorganic perovskites at room temperature without compromising their functional properties. Their findings demonstrate the potential of this class of semiconductors for manufacturing next-generation deformable electronics and energy systems in the future.

Electronic sensor the size of a single molecule a potential game-changer

Researchers have developed a molecular-sized, more efficient version of a widely used electronic sensor, in a breakthrough that could bring widespread benefits.

Could future AI crave a favorite food?

Can artificial intelligence (AI) get hungry? Develop a taste for certain foods? Not yet, but a team of researchers is developing a novel electronic tongue that mimics how taste influences what we eat based on both needs and wants, providing a possible blueprint for AI that processes information more like a human being.

Separating molecules requires lots of energy. This new, heat-resistant membrane could change that

A research team has created a new, heat-resistant membrane that can withstand harsh environments -- high temperatures, high pressure and complex chemical solvents -- associated with industrial separation processes. It could eventually be used as a less energy intensive alternative to distillation and other industrial processes that separate molecules that ultimately serve as ingredients in medicine, chemicals and other products.

Next-generation printing: Precise and direct, using optical vortices

Researchers have succeeded in printing uniformly sized droplets with a diameter of approximately 100 µm using a liquid film of fluorescent ink. This ink, with a viscosity roughly 100 times that of water, was irradiated with an optical vortex, resulting in prints of exceptional positional accuracy at the micrometer scale.

Novel battery technology with negligible voltage decay

A pivotal breakthrough in battery technology that has profound implications for our energy future has been achieved.

Accelerating sustainable semiconductors with 'multielement ink'

Scientists have demonstrated 'multielement ink' -- the first 'high-entropy' semiconductor that can be processed at low-temperature or room temperature. The new material could enable cost-effective and energy-efficient semiconductor manufacturing.