Lecture

Bipolar Junction Transistors: Small Signal Model and Applications

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In course

MICRO-312: Physics of semiconductors devices

Les étudiants savent expliquer la physique des composants semiconducteurs, tels que diodes, transistors et composants MOS. Ils les utilisent dans des circuits électroniques fondamentaux tels qu'inverseurs et ampli. ...

Description

This lecture covers the small signal model of bipolar junction transistors (BJTs), focusing on their structure and operation. The instructor begins by explaining the basic components of a BJT, including the emitter, base, and collector, and how they interact to allow current flow. The lecture details the active mode of operation, emphasizing the relationship between input and output characteristics, including the exponential behavior of the base-emitter junction. The instructor introduces the Ebers-Moll model and discusses the significance of parameters such as transconductance and output conductance. The lecture also explores the concept of heterojunction bipolar transistors (HBTs), highlighting their advantages over traditional BJTs, particularly in terms of gain and speed. The discussion includes the impact of doping and material selection on transistor performance. Finally, the instructor addresses potential issues such as punch-through and current crowding in power BJTs, presenting solutions like comb structures to mitigate these effects. Overall, the lecture provides a comprehensive overview of BJTs and their applications in electronic circuits.

Instructor

Pierre-André Besse

Teaching & PhD Past EPFL PhD Students Klaus Ehrmann Courses La science quantique : une vision singulière MICRO-444 Students understand the characteristics of quantum science. They master the formalism and use it in basic quantum systems: quantum wells, wires, dots or qubits. Physics of semiconductors devices MICRO-312 The students are able to explain the physics of semiconductor devices like diodes, transistors, and MOS devices. They use such devices in fundamental electroni

Official source

Ontological neighbourhood

Physics

Condensed matter physics: Solid-state physics

Related concepts (32)

Bipolar junction transistor

A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching. BJTs use two p–n junctions between two semiconductor types, n-type and p-type, which are regions in a single crystal of material.

Transistor

A transistor is a semiconductor device used to amplify or switch electrical signals and power. It is one of the basic building blocks of modern electronics. It is composed of semiconductor material, usually with at least three terminals for connection to an electronic circuit. A voltage or current applied to one pair of the transistor's terminals controls the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal.

History of the transistor

A transistor is a semiconductor device with at least three terminals for connection to an electric circuit. In the common case, the third terminal controls the flow of current between the other two terminals. This can be used for amplification, as in the case of a radio receiver, or for rapid switching, as in the case of digital circuits. The transistor replaced the vacuum-tube triode, also called a (thermionic) valve, which was much larger in size and used significantly more power to operate.

Field-effect transistor

The field-effect transistor (FET) is a type of transistor that uses an electric field to control the flow of current in a semiconductor. FETs (JFETs or MOSFETs) are devices with three terminals: source, gate, and drain. FETs control the flow of current by the application of a voltage to the gate, which in turn alters the conductivity between the drain and source. FETs are also known as unipolar transistors since they involve single-carrier-type operation.

Doping (semiconductor)

In semiconductor production, doping is the intentional introduction of impurities into an intrinsic semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor. Small numbers of dopant atoms can change the ability of a semiconductor to conduct electricity. When on the order of one dopant atom is added per 100 million atoms, the doping is said to be low or light.

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