Analogue Electronics Circuits

Analogue Electronics Circuits 1
Student
Instructor
Analogue and digital electronics
Date

Analogue Electronics Circuits 2
Introduction
Semiconductor materials are useful when designing solid electronic components which utilize
fundamental properties of materials. Most commonly used semiconductor materials are silicon and
germanium. Behavioral characteristics of semiconductor devices are easily manipulated to conform
into required properties for applications. Such manipulation is achieved through doping
semiconductors with impurities. Electrically conductivity in semiconductors is based on the mobile
electrons and holes commonly referred to as charge carriers. Over the decades, advancement is
technology has resulted to production growth of semiconductors so as to meet the demand in their
applications. This report entails in-depth understanding of diodes and bipolar junction transistors BJT,
and selected applications. The simulation was done in Multisim software and analyzed.
Diodes
Diodes are devices belonging in the family of semiconductor that is made of two differently doped
materials namely; P-type and N-type. The P-type region encompasses holes as the majority charge
carriers and electrons as the minority charge carriers. Contrary, the N-type region accommodates
electrons as the majority charge carriers and holes as the minority charge carriers. Holes, formed by
location voids of diffused electrons, are electrically negative. The junction interface formed between
two diode regions is known as depletion layer. The depletion layer is formed when p-region and N-
region are structurally joined. In the process of formation, holes in P-region diffuse into the N-region
equally do electrons from N-region diffuse into the P-region due to mutual attraction of charges with
opposite polarity. In addition to mutual attraction, diffusion is also realized because majority charge
carrier concentration. As the diffusion proceeds, potential different is developed across the depletion
layer impeding further diffusion. An equilibrium level is achieved with the voltage across the
depletion layer, also known as potential barrier, blocking majority charge carriers from diffusing
across to the next region. In the depletion layer, there are no mobile charge carriers.
Diode equations below explain the amount of current flowing through the diode given the voltage
across and the junction’s temperature with associated physical constants.
I D =I s ( eq V D /NKT
−1 )
Where,
I D −is Diode Current
I S−is the saturation current
e−is the Eulers constant
q−is the charge of an electron
V D−Voltage across thediode
N−Emission coefficient
k −Boltzman n' s constant
T −Junctiontemperature ∈Kelvin

Analogue Electronics Circuits 3
From the equation above, kT
q is the voltage contribution within P-N junction caused by the influence
of temperature, hence thermal voltage (V ¿¿ T ) ¿. Thermal voltage is about 26mV at room
temperature (ARTICLES et al., 2019).
Characteristic of a diode.
The basic diode is a semiconductor which permits unidirectional flow of current when subjected
under biasing voltage. There are two types of biasing the diode namely; forward bias and reverse bias.
In forward biasing, the voltage source is connected with the diode by connecting anode to the P-
region and cathode to the N-region. However, little current will flow at lower voltage and increases
exponentially as the biasing voltage races over the potential barrier across the depletion layer.
Potential barrier varies with semiconductor materials used to make the diode. For instance, voltage of
about 0.6 to 0.7V is the permissible voltage supplied by the voltage source to breach the barrier, while
for the germanium, the value is about 0.2V. Charge carriers in forward bias consists of majority holes
and electrons. Accordingly, the diode behaves like a conductor when biasing voltage exceeds the
potential barrier. At this point, current increases linearly with increase in biasing voltage.
Similarly, diodes characteristically block flow of current under influence of the reverse biasing
voltage. In this configuration cathode of the voltage source is connected with P-region terminal of the
diode while anode is connected with the N-region of the diode. This type of configuration impacts
depletion layer by widening it. Expansion of the depletion layer is explained by drifting of majority
charge carriers away from the junction as they get attracted with the opposite polarity charged from
the reverse biasing voltage. However, for a practical diode, small reverse current leaks across the
depletion layer. This reverse current is formed by the contribution of minority charge carriers.
Minority charge carriers are electrons located in the P-region and holes located in the N-region. As the
reverse biasing voltage increases, the influence of electric field across the depletion layer becomes
greater until a point where the diode becomes conductive. The peak reverse voltage at which diode
enters conduction mode when reverse biased is known as breakdown voltage.
Graphically, the characteristics of a diode can be represented as below.

Analogue Electronics Circuits 4
Applications of diodes
Inherent characteristics of diodes enable these type of semiconductor to be used over an extensive
range of applications. Applicability of diodes narrows down to individual characteristics of the
specific diode. For instance, in power rectification, special class of diodes known as rectifier diodes
are used while for voltage regulation, zener diodes are preferred.
Voltage rectification
Rectifier is a circuit that allows alternating current and or voltage to flow with the same polarity and
in the same direction (ElProCus - Electronic Projects for Engineering Students, 2019).
Power diodes are connected together or singly configured to produce two types of rectifier circuits
namely; Half wave and bridge rectifier.
A half wave diode rectifier consist of a single diode connected in series with the load and the AC
power source. Rectification is achieved by allowing either positive or negative half cycle of the
alternating signals to pass through it and chopping off the other opposite half cycle. Accordingly, the
diode is forward biased during the conducting half cycle and become reverse biased during non-
conducting half cycle. By doing so, the load current becomes unidirectional. The output voltage
profile is irregular because of spikes that are in phase with the conducting half cycle as below