AVIA 1083 W2

BJT stands for…?

Bipolar Junction Transisto

What are the three terminals of a BJT?

Base (B), Collector (C), and Emitter (E)

Two types of BJT

NPN and PNP

In a BJT, what is the relationship between emitter current (IE), base current (IB), and collector current (IC)?

IE = IB + IC

Formula for the DC current gain (β or hFE) of a transistor?

β or hFE = IC / IB

What does the base-emitter forward-bias voltage vs. Current graph look like?

Very similar to the forward bias graph of a Silicon diode

At what VBE does a silicon BJT start to conduct significant current?

Approx. 0.6 Vdc (after which current increases rapidly).

What is meant by the "constant current characteristic" of a transistor's output?

The transistor's output current (IC) remains relatively constant while the Collector-Emitter voltage (VCE) changes

Formula for static (DC) input resistance of a transistor

DC Input Resistance = VBE / IB

Formula for dynamic (AC) input resistance of a transistor

AC Input Resistance = ΔVBE / ΔIB

Formula for static (DC) output resistance of a transistor

DC Output Resistance = VCE / IC

Formula for dynamic (AC) output resistance of a transistor

AC Output Resistance = ΔVCE / ΔIC

Symbol for static transistor gain?

hFe

Symbol for dynamic transistor gain?

hfe

Formula for static current gain

hFE = IC / IB

Formula for dynamic current gain

hfe = ΔIC / ΔIB

For most small-signal transistors, what is the typical maximum collector current range?

1 to 10 mA

Why is it important to design circuits based on the minimum value of transistor gain?

To ensure successful operation of the circuit across different transistors (since gain varies)

Darlington pair

A compound structure consisting of two bipolar transistors connected so that the current amplified by the first transistor is amplified further by the second

Main advantage of a Darlington pair?

It gives a much higher common-emitter current gain than each transistor taken separately

In an integrated Darlington pair, what do the two transistors share?

They can use a shared collector.

3 basic circuit configurations for transistor amplification

Common-Emitter, Common-Collector, and Common-Base.

In the Common-Emitter configuration, where is the input applied and where is the output taken from?

[CE] Input: between Base and Emitter. Output: between Collector and Emitter.

Key characteristics of a Common-Emitter amplifier? (Voltage gain, current gain, phase shift)

[CE] Voltage Gain: Medium/High (≈40); Current Gain: High (≈200); Phase Shift: 180°.

Typical application for a Common-Emitter amplifier

General purpose, AF (Audio Frequency) and RF (Radio Frequency) amplifiers.

In the Common-Collector configuration, where is the input applied and where is the output taken from?

[CC] Input: directly to the Base. Output: from the Emitter load.

What are the key characteristics of a Common-Collector amplifier? (Voltage gain, input/output resistance, phase shift)

[CC] Voltage Gain: None (≈1); Input Resistance: High (≈100 kΩ); Output Resistance: Low (≈100 Ω); Phase Shift: 0°.

Typical application for a Common-Collector amplifier?

Impedance matching (input to output)

In the Common-Base configuration, where is the input applied and where is the output taken from?

[CB] Input: between Base and Emitter. Output: between Base and Collector

What are the key characteristics of a Common-Base amplifier? (Voltage gain, current gain, phase shift)

[CB] Voltage Gain: High (≈200); Current Gain: None (actually attenuates, negative gain); Phase Shift: 0°.

Typical application for a Common-Base amplifier?

RF and VHF (Very High Frequency) amplifiers

Which transistor amplifier configuration produces the highest current and power gain?

Common-Emitter

Which transistor amplifier configuration is best for impedance matching?

Common-Collector

Which transistor amplifier configuration "attenuates" the input signal (negative current gain)?

Common-Base

IC max

IC max: maximum collector current

VCE max

VCE max: maximum collector-emitter voltage

PTOT max

PTOT max: maximum device power dissipation

bFE represent…?

[bFE] typical value of common-emitter current gain

A bipolar transistor has a common-emitter current gain of 125. If the collector current is 50 mA, what is the base current?

IB = IC / β → 50 mA / 125 = 0.4 mA (or 400 µA)

To amplify an input signal in a Common-Emitter circuit, how must the junctions be biased?

[CE] The Base-Emitter junction must be forward biased, and the Base-Collector junction must be reverse biased

What is the purpose of biasing a transistor?

Biasing establishes the proper operating conditions for the transistor and stabilizes the base so the input signal operates over the linear portion of the transistor

In the voltage divider bias method, which components accomplish biasing?

Two resistors (R1 and R2) acting as a voltage divider, along with the power supply (Vcc)

How does holding the input to the Base (IB) at a constant steady voltage help the transistor?

It allows for the best stability in the transistor

Where are Common-Emitter amplifiers often used?

Audio, radio, and TV applications

What effect does the Emitter resistor (RE) have on the output of a Common-Emitter amplifier?

It reduces the gain of the transistor (because the transistor sees a lower difference between base and emitter voltage)

How is the loss of gain from RE corrected?

By adding a capacitor (C2) in parallel with RE

What does the Emitter bypass capacitor (C2) do?

It provides another path for the AC signal current to flow, allowing more gain in the transistor

What happens when a transistor is operated beyond its normal range (above or below)?

The transistor will clip the wave

What is the result of clipping in an audio circuit?

Poor audio quality (distortion)

In Class A amplification, what is the conduction output wave angle?

360° (conducts over the entire input cycle)

Where is the Q-point located for a Class A amplifier?

At the centre point of the load line

What is the overall efficiency and signal distortion of a Class A amplifier?

Efficiency: Poor (5–40%). Distortion: None (if correctly biased)

In Class B amplification, what is the conduction output wave angle?

180° (amplifies only half of the input wave cycle)

Where is the Q-point located for a Class B amplifier?

Exactly on the Vout axis

What is the overall efficiency and signal distortion of a Class B amplifier?

Efficiency: Better (40–70%). Distortion: At the X-axis crossover point

In Class C amplification, what is the conduction output wave angle?

Less than 90° (conducts less than 50% of the input signal)

Where is the Q-point located for a Class C amplifier?

Below the Vout axis

What is the overall efficiency and signal distortion of a Class C amplifier?

Efficiency: Higher (70–90%). Distortion: Large amount

What is the typical application for a Class C amplifier?

RF transmitters operating at a single fixed carrier frequency (distortion is controlled by a tuned load)

In Class AB amplification, what is the conduction output wave angle?

180° (but also conducts a small amount on the other half).

Where is the Q-point located for a Class AB amplifier?

Slightly above the Vout axis

What is the main advantage of Class AB over Class B?

AB greatly minimizes or eliminates the crossover distortion (the "dead zone" is reduced).

Field Effect Transistor (FET)

A transistor that uses an electric field to control the shape and conductivity of a channel of one type of charge carrier in a semiconductor material

3 terminals of a FET

Gate (G), Drain (D), and Source (S)

How does a FET control the flow of electrons or holes from source to drain?

By affecting the size and shape of a "conductive channel" created by voltage applied across the gate and source terminals

2 main types of FETs

JFET (Junction Field Effect Transistor) and MOSFET (Metal-Oxide-Semiconductor FET)

JFET

The simplest type of field-effect transistor; a three-terminal semiconductor device used as an electronically-controlled switch, amplifier, or voltage-controlled resistor

How are JFETs controlled, unlike bipolar transistors?

They are exclusively voltage-controlled and do not need a biasing current

How is the channel "pinched" in a JFET?

By applying a reverse bias voltage to the gate terminal, which impedes or switches off the electric current

What is the normal state of a JFET when there is no potential difference between its gate and source?

It is usually ON

What happens when a potential difference of the proper polarity is applied between the gate and source?

The JFET becomes more resistive to current flow (less current flows in the channel)

Why are JFETs sometimes referred to as depletion-mode devices?

Because they are normally ON and a reverse bias voltage is required to deplete the channel and turn them off

The Gate-Source junction of a JFET is effectively what?

A reverse biased P-N junction

In a JFET, what surrounds the channel of P or N material?

The opposite type of material, which has a connection called the Gate

How is the effective width of the JFET channel controlled?

By the amount of charge applied to the Gate (which controls the depletion region)

What happens to the depletion region as the negative potential difference at the gate increases?

Depletion region grows larger (like a reverse-biased diode), eventually cutting off the flow in the channel and turning the JFET OFF

What is a major advantage of JFETs compared to bipolar transistors?

Much higher input resistance (ideal where high input resistance is required)

In the JFET graph of Drain Current (ID) vs. Gate-Source Voltage (VGS), what happens to the current as the negative potential difference becomes greater?

The current through the JFET is reduced

In the JFET output characteristics graph (ID vs. VDS), what is indicated at the end of each curve?

The negative voltage applied to the Gate in comparison to the Source (VGS)

How is the constant current achieved in a JFET?

By the reverse bias control of the Gate to Source

What is the gain in a JFET normally expressed in terms of?

Forward Transconductivity (gfs or Yfs)

What is the formula for static (DC) forward transconductivity?

ID / VGS

Unit of transconductivity

The siemens (S), where 1 siemens = 1 ampere per volt

If ID = 12 mA and VGS = 1 V, what is the static forward transconductivity?

12 mA / 1 V = 12 mS

What is the formula for dynamic (AC) forward transconductivity?

ΔID / ΔVGS

Using the example from the PDF: When VGS changes by 2.5 V and ID changes by 12 mA (from the graph), what is the dynamic forward transconductivity?

12 mA / -2.5 = 2 mS

What does MOSFET stand for?

Metal-Oxide-Semiconductor Field-Effect Transistor

What is a MOSFET used for?

Amplifying or switching electronic signals

4 terminals of a MOSFET

Source (S), Gate (G), Drain (D), and Body (B)

Why is a MOSFET often treated as a three-terminal device?

Because the body (substrate) is often connected to the source terminal.

What are the two types of MOSFET channels?

N-channel and P-channel

In the MOSFET construction diagram, what separates the Gate from the P-type Silicon?

A metal layer and an oxide layer

Region that forms under the oxide in a MOSFET?

The Depletion Region

Integrated Circuit (IC)

A set of electronic circuits on one small plate ("chip") of semiconductor material, normally silicon.

What are three other common names for an integrated circuit?

Chip, microchip, or monolithic integrated circuit

2 main advantages of ICs over discrete circuits

Cost and performance

Why is IC cost low?

Millions of transistors are printed as a complete unit by photolithography, not constructed one at a time

Why is IC performance higher?

Components switch quickly and consume little power

2 classifications of integrated circuits

Linear (Analogue) and Digital (Logic) type circuits

Scale of integration

The relative size of a digital IC in terms of the number of active devices (logic gates) it contains