2-ELECTRONICS II MIDTERM

unijunction transistor

s a three-terminal semiconductor device characterized by a single PN junction. It is primarily used for switching and timing applications, functioning as an electrically controlled switch rather than an amplifier

double based diode

unijunction transistor is also called

emitter base 1 base 2

three terminal of ujt

negative resistance

The UJT exhibits unique properties such as _________, making it suitable for various electronic applications like oscillators and pulse generators.

heavily, lightly

(ujt) The emitter is ______ doped while the n-region is ________ doped. Thus, the resistance between base terminals is very high when emitter terminal is open.

off

(ujt) When the voltage VBB is applied with emitter open. A potential gradient is established along the n-type silicon bar. As the emitter is located close to the base B2, thus a major part of VBB appears between the emitter and base B1. The voltage V1 between emitter and B1, establishes a reverse bias on the PNjunction and the emitter current is cut off, but a small leakage current flows from B2 to emitter due to minority charge carriers. Thus, the device is said to be in _____ state.

off state

ujt emitter open

on

(ujt) When a positive voltage is applied at the emitter terminal, the pn-junction will remain reverse biased till the input voltage is less than V1. A soon as the input voltage at emitter exceeds V1, the pn-junction becomes forward biased. Under this condition, holes are supplied from p-type region into the n-type bar. These holes are repelled by positive B2 terminal and attracted towards the B1 terminal. This increase in the number of holes in the emitter to B1 region results in the decrease of resistance of this section of the bar. Because of this, the internal voltage drop from emitter to B1 region is reduced, thus the emitter current (IE) increases. As more holes are supplied, a condition of saturation is reached. At the point of saturation, the emitter current is limited by the emitter power supply. Now, the device is conducting, hence said to be in ______ state

on state

ujt with emitter at positive potential

conductivity modulation

The additional current reduces resistance in the base region, further enhancing current flow

negative resistance

As emitter current increases, it causes a decrease in voltage across B1, resulting in a regenerative effect that can lead to saturation

reverse bias

ujt with emitter open
pn juction:__________

high interbase resistance

ujt with emitter open

resistance:_________

emitter

ujt with emitter open

current flow: small leakage current from B2 to ______

b1

ujt with emitter open

Voltage: Most of the applied voltage (VBB) appears across ______

forward biased

UJT with Emitter at Positive Potential

pn junction: ________

conductivity modulation

UJT with Emitter at Positive Potential

Current flow: Increased emitter current (IE) due to _________

saturation

UJT with Emitter at Positive Potential

Regenerative effect: Can lead to _____

inter base resistance

(ujt) The resistance of silicon bar is called as the

4 to 10 k ohms

inter base resistance value

rb1

(ujt) is the resistance of the bar between emitter and B1 region. The value of this is variable and depends upon the bias voltage across the pn-junction

rb2

(ujt) is the resistance of the bar between emitter and B2 region.

rbb=rb1+rb2

With no voltage applied to the UJT, the value of inter-base resistance is given by:

n= V1/VBB

The intrinsic stand-off ration (ƞ) of UJT is given by:

intrinsic stand off ratio

Defined as 𝜼 = RB1 RBB , this ratio varies from 0.4 to 0.8 across different devices and influences how much voltage is required to trigger conduction.

field effect transistor

is a type of transistor that uses an electric field to control the flow of current in a semiconductor.

field effect transistor

voltage controlled transistor

source, drain, gate

3 terminals of FET

source

FET

Where current enters the transistor.

drain

FET

Where current exits the transistor.

gate

FET

The control terminal that modulates the conductivity of the channel between the source and drain.

junction fet jfet

type of FET that Utilizes a PN junction to control current flow. It can be either N-channel or P-channel.

metal oxide semiconductor fet mosfet

(FET) Features an insulating layer of oxide between the gate and the channel, allowing for high input impedance.

enhancement mode

mosfet type

Conducts when a positive gate voltage is applied.

A voltage applied to the gate creates a conducting channel in the semiconductor, enabling current flow

depletion mode

mosfet type

Conducts when no gate voltage is applied but can be turned off by applying a negative gate voltage

The conducting channel exists by default, which diminishes as a voltage is applied to the gate.

n channel jfet

The channel is formed by electrons. A positive gate-to-source voltage enhances the channel conductivity by attracting electrons to the channel region, allowing current to flow.

drain and source connected to n type

gate connected to p type

p channel jfet

The channel is formed by hole. A negative gateto-source voltage enhances the channel conductivity by attracting holes.

drain and source connected to p type

gate connected to n type

mosfet

features a metal gate insulated by a thin oxide layer from the semiconductor. It has two operating modes: enhancement mode and depletion mode.

light emitting diode

is a semiconductor device that emits light when an electric current passes through it.

light emitting diode

They are constructed from a p-n junction, which allows current to flow in one direction, leading to the emission of light as electrons recombine with holes.

photons

the energy in led is released in the form of

electroluminescence

is an optical phenomenon, and electrical phenomenon where a material emits light in response to an electric current passed through it.

aluminum alloys

to obtain red, orange and yellow light, in led

indium alloys

to get green, blue and white light in led

AlGaInP

elements to obtain red, orange and yellow light, in led

InGaN

elements Used for green, blue, and white LEDs.

liquid crystal display

is a flat display screen used in electronic devices such as laptop, computer, TV, cellphones and portable video games. As the name says liquid crystal is a material which flows like a liquid and shows some properties of solid.

nematic

In Liquid crystal display (LCD) __________ type of liquid crystal molecular arrangement is used in which molecules are oriented in some degree of alignment

liquid crystal display

Two glass plates with a thin layer of liquid crystal sandwiched between them.

• Top and bottom glass plates have polarizers oriented at right angles to each other.

• Electrodes are placed on the inner surfaces of the glass plates to apply a voltage to the liquid crystal.