Name: bjt current-voltage curves in common emitter
Uploaded: 2024-07-08T13:20:31.000Z
Duration: 1 min 17 s
Channel: JoVE

Consider the common-emitter configuration of the BJT.
The voltage and current dependencies are measured experimentally to understand the current-voltage characteristics.
For the input characteristics, the base-emitter voltage is varied while keeping the collector-emitter voltage constant.
The resulting graph shows the Shockley-type dependence of the collector current on the base-emitter voltage.
The output characteristics represent the collector current as a function of the collector-emitter voltage, keeping the base current constant.
The saturation region corresponds to a small collector-emitter voltage where the collector current drops towards zero. Here, the transistor&#39;s resistance between the collector and emitter terminals is small.
When the collector-emitter voltage increases, the transistor enters the active region. Here, the transistor&#39;s collector-emitter resistance becomes infinitely high while the collector current remains independent of the collector-emitter voltage.
However, in practice, a slight increase in the collector current is noticed, which is due to the widening of the depletion region and shortening of the base length.
This is known as the Early effect, leading to a finite output resistance of the transistor.

characteristics of bjt

Characteristics of BJT

The Bipolar Junction Transistor (BJT), specifically in a common-emitter configuration, exhibits distinct current-voltage characteristics crucial for understanding its behavior in electronic circuits. These characteristics are established through experimental measurements of voltage and current relationships.
For input characteristics, the base-emitter voltage is varied, maintaining a constant collector-emitter voltage. This setup reveals a Shockley-type dependence of the collector current on the base-emitter voltage. As the base-emitter voltage increases, so does the collector current, but under a controlled condition of constant collector-emitter voltage.
The output characteristics are then observed by plotting the collector current against the collector-emitter voltage while keeping the base current fixed. This relationship highlights several operational regions of the BJT. In the saturation region, the collector-emitter voltage is low, causing the collector current to approach zero, indicating minimal resistance between the collector and emitter terminals.
As the collector-emitter voltage rises, the transistor transitions into the active region, exhibiting an infinitely high collector-emitter resistance. The collector current remains relatively stable regardless of changes in the collector-emitter voltage. However, a slight increase in the collector current can be observed, which can be attributed to the early effect. This phenomenon involves a widening of the depletion region and a reduction in the base width, increasing the saturation current and thus introducing a finite output resistance.
These characteristics define the operating conditions and performance of BJTs in various applications, making them fundamental components in designing and analyzing electronic circuits.

Consider the common-emitter configuration of the BJT.
The voltage and current dependencies are measured experimentally to understand the current-voltage ...

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bjt current-voltage curves in common emitter

The Bipolar Junction Transistor (BJT) in a common-emitter setup is studied by measuring its current-voltage curves. These measurements show how the transistor responds when voltage and current are changed in a controlled way. They are key to understanding how a BJT works in electronic circuits.

The input characteristics are found by varying the base-emitter voltage while keeping the collector-emitter voltage constant. This test shows a Shockley-type relationship between the collector current and the base-emitter voltage. As the base-emitter voltage rises, the collector current also increases under the same collector-emitter voltage.

The output characteristics are found by plotting collector current against collector-emitter voltage while the base current is fixed. These curves show the main operating regions of the BJT. In saturation, the collector-emitter voltage is low, so the collector current approaches zero and the resistance between collector and emitter is minimal.

As the collector-emitter voltage increases, the transistor moves into the active region. Here, the collector-emitter resistance is very high, and the collector current stays nearly constant even when the collector-emitter voltage changes. A small rise in collector current can still appear because of the early effect.

The early effect happens when the depletion region widens and the base width becomes smaller. This raises the saturation current and gives the device a finite output resistance. Together, these input and output curves define the operating conditions and performance of BJTs in circuit design and analysis.

BJT Current-Voltage Curves in Common Emitter

bjt-current-voltage-curves-in-common-emitter

bipolar junction transistor

BJT Structure and Carrier Flow

Bipolar junction transistors are important parts of electronic circuits. They help make amplifiers, memories, and microprocessors work. A BJT can be built as either NPN or PNP, depending on its doping pattern, which means the type of impurities added to the material. A BJT has three layers: the emitter, base, and collector. It also has two p-n junctions, so the device has a sandwich-like structure. The emitter is heavily doped so it can inject charge carriers into the base. The base is very...

configurations of bjt

BJT Amplifier Modes and Uses

Bipolar Junction Transistor (BJT) configurations are defined by which terminal is shared by the input and output circuits. The shared terminal can be the base, emitter, or collector. Each setup has different electrical behavior and fits different circuit needs. In the common base configuration, the base is the common terminal. This setup has high voltage gain, so it can work well in single-stage amplifier circuits such as microphone pre-amplifiers. It also reduces the input current signal...

working principle of bjt

PNP BJT Current Flow in Active Mode

PNP bipolar junction transistors control current flow by moving charge carriers between the emitter, base, and collector. In a common-base setup, the transistor can amplify or switch electronic signals when it operates in active mode. In a PNP transistor, the emitter is heavily doped with holes, which are positive charge carriers. The base is lightly doped with electrons, which are negative carriers. A forward bias across the emitter-base junction lowers the potential barrier and lets holes...

The Bipolar Junction Transistor (BJT) in a common-emitter setup is studied by measuring its current-voltage curves. These measurements show how the transistor responds when voltage and current are changed in a controlled way. They are key to understanding how a BJT works in electronic circuits. The input characteristics are found by varying the base-emitter voltage while keeping the collector-emitter voltage constant. This test shows a Shockley-type relationship between the collector current...

modes of operations of bjt

BJT Biasing: Active to Inverted Mode

A bipolar junction transistor (BJT) works in four modes that depend on how its two junctions are biased. Those modes are active, saturation, cut-off, and inverted. The biasing pattern controls whether the transistor amplifies current or acts like a switch. Active mode is the most common mode for amplification. In this mode, the emitter-base junction is forward-biased and the base-collector junction is reverse-biased. Electrons move from the emitter into the base, while the collector blocks...

frequency response of bjt

BJT Amplifier Response at Low and High Freq

A BJT amplifier’s response changes with frequency in a common-emitter circuit. Its behavior at low frequencies and high frequencies depends on the circuit’s equivalent model. These models help explain how the transistor handles AC signals. At low frequencies, the DC bias point sets the transistor’s operation. The emitter-base voltage, base current, and collector current define this bias point. The load line also shapes how the amplifier works, using the applied voltage and load resistance. <br...

cut-off frequency of bjt

BJT Frequency Limits and Gain Drop

BJT frequency limits show when a bipolar junction transistor stops keeping a steady gain. These limits matter because they mark the shift from the pass band to the stop band in an electronic signal. They help explain why a transistor may amplify one range of frequencies well and weaken signals at higher frequencies. The alpha cut-off frequency applies to the common-base configuration. At low frequencies, the current gain alpha stays stable. Beyond this upper-frequency limit, alpha drops and...

switching of bjt

BJT as a Digital On-Off Switch

Bipolar junction transistors (BJTs) can work as digital on-off switches in electronic circuits. In this mode, the transistor moves between cut-off and saturation. These two states match the off and on positions of an ideal switch. In cut-off mode, both the emitter-base junction and the collector-base junction are reverse-biased. This blocks current flow through the transistor and keeps it off. Circuits use this state when no signal transmission is needed, which helps maintain a low-power...

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Common-Emitter BJT Voltage Gain

Bipolar junction transistors, or BJTs, can act as amplifier parts when they work in the active region. In this mode, a small change in base-emitter voltage controls a larger collector current. That makes the transistor act like a voltage-controlled current source and lets it boost a weak signal into a stronger one. A common-emitter BJT amplifier uses that current change to create voltage gain. The output current flows through a load resistor, and the voltage drop across that resistor sets the...

small-signal analysis of bjt amplifiers

BJT Amplifier Gain and Input Resistance

BJT amplifier gain and input resistance can be analyzed with a small-signal model. In the active region, a bipolar junction transistor is used for linear amplification. Its base-emitter voltage includes a DC bias and a small AC signal. That input produces a collector current with both DC and AC parts. When the AC input signal is much smaller than the thermal voltage VT, the small-signal approximation applies. This makes it possible to find the AC collector current from the DC collector current...

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Field Effect Transistor Types and Uses

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JFET Output Regions and Current Control

JFET output characteristics show how drain current changes with drain-source voltage and gate-source voltage. In a junction field effect transistor, the gate-source voltage controls the drain current. When the drain and gate voltages are set to zero, the device is in equilibrium and no net current flows. With the gate voltage held at zero, the drain current rises linearly as the source-drain voltage increases. This linear part is called the Ohmic region. In this region, the JFET acts like a...

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JFET Gate-Source Bias and Current Control

JFET gate-source bias controls current flow in a junction field effect transistor. A JFET uses one carrier type and comes in N-channel or P-channel forms. In both cases, the channel is surrounded by PN junctions, and those junctions help control how current moves through the device. In an N-channel JFET, N-type material forms the channel on a P-type substrate. The gate is made of P-type material. Biasing this device means applying a negative voltage to the gate relative to the source. That...

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MOSFET Current Control in Electronics

The MOSFET is a semiconductor device that controls electrical current in modern electronics. It is also called an IGFET or MISFET. The three main terminals are the source, drain, and gate. MOSFETs are classified as n-channel or p-channel devices. The type depends on the doping of the substrate and the source or drain regions. In an n-MOSFET, the source and drain are n-type regions separated from a p-type substrate by reverse-biased p-n diodes. The gate is built from a metal plate over an...

characteristics of mosfet

MOSFET Structure and Operating Regions

MOSFETs, or metal-oxide-semiconductor field-effect transistors, are important parts of electronic circuits. They are used to amplify and switch signals. Their behavior depends on several design features, including channel size, oxide thickness, junction depth, and substrate doping. Channel length and channel width shape how much current a MOSFET can carry and how fast it can switch. Shorter channels usually allow faster operation. The oxide thickness also matters. This silicon dioxide layer...

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Enhancement-mode MOSFETs are MOSFETs that work as controlled electronic switches. They belong to the metal-oxide semiconductor field-effect transistor family. These devices come in two forms: n-channel and p-channel, and each one is used for a different polarity of operation. At zero gate-source voltage, or Vgs, an enhancement-mode MOSFET is usually non-conductive. In that default off state, no current flows between the drain and source terminals. When a positive Vgs is applied, it creates an...

mosfet: depletion mode

Depletion MOSFET Channel Control

Depletion-mode MOSFETs are normally on transistors with a built-in channel that conducts current without gate bias. They work differently from enhancement-mode MOSFETs, which need a positive gate-source voltage, or V gs, to turn on. In a depletion device, the channel is already open because the channel doping creates a low-resistance path between the drain and source. These devices behave much like junction field-effect transistors, or JFETs. The channel conductivity is set by the material...

mosfet amplifiers

MOSFET Gain and Biasing

MOSFET gain and biasing shape how a MOSFET amplifier works. When a MOSFET operates in its active region, it acts like a voltage-controlled current source. The gate-to-source voltage sets the drain current, and that behavior supports transconductance amplification. The output current then flows through a load resistor. That load resistor turns the circuit into a voltage amplifier. The output voltage is found by subtracting the voltage drop across the load resistor from the supply voltage, so...

small-signal analysis of mosfet amplifiers

small-signal-analysis-of-mosfet-amplifiers

MOSFET Amplifier Gain and Signal Distortion

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key terms and concepts

Learn how a BJT in common-emitter mode is tested with input and output curves, including saturation, active region, and the early effect.

BJT Current-Voltage Curves in Common Emitter | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

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BJT Current-Voltage Curves in Common Emitter

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