Basic Circuit Elements:
1. Passive Elements:
a. Resistor: It resists the flow of current through it. It will have a voltage drop when measured
across it.
b. Inductor: It holds the charge in the form of magnetic field.
c. Capacitor: It holds the charge in the form of electric field.
2. Active Elements:
a. Voltage Source: Dependent and Independent voltage sources.
b. Current Source: Dependent and Independent current sources.
Voltage – Current (V-I) Characteristics of a Resistor
Voltage is directly proportional to Current and the proportionality constant is called Resistance (R).
It has the units of Ohms (Ω) 1 Ω= 1 V/A
According to Ohm’s law : V=IR
Voltage-Current Relation in a Capacitor
Voltage is proportional to the integral of Current and its constant is called capacitance, has the units of
Farads (F)
Voltage-Current Relation in an Inductor
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➢ Define Semiconductor. Explain different types of Semiconductors and draw the
atomic Structure.
• Semiconductors are materials whose conductivity lies between conductors and
insulators.
• At absolute zero temperature, semiconductors exhibit the property of insulators but
at high temperature semiconductors behaves as controlled conductors.
• Semiconductors are classified as
o Intrinsic semiconductors (undoped semiconductor)
•
•
•
A semiconductor in an extremely pure
form is known as an intrinsic
semiconductor.
In an intrinsic semiconductor, even at
the room temperature, hole-electron
pairs are created.
When the electric field is applied
across an intrinsic semiconductor the
current conduction takes place by free
electrons and holes as shown in fig.
o Extrinsic semiconductors (doped with an impurity)
The conducting properties of an intrinsic semiconductor can be increased by adding small amount of
suitable impurities to it. It is then called impure or extrinsic semiconductor.
▪ N-type
When a small amount of penta-valent impurity is added to a pure semiconductor, it is known as n
type semiconductor.
▪ P-type semiconductors.
When a small amount of trivalent impurity is added to a pure semiconductor, it is called p
semiconductor.
➢ What is P-N Junction?
A P-N junction is an interface or a boundary between two semiconductor material
types, namely the p-type and the n-type, inside a semiconductor.
•
•
•
In a semiconductor, the P-N junction is created by the method of doping.
The p-side or the positive side of the semiconductor has an excess of holes, and
the n-side or the negative side has an excess of electrons.
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•
An n -type material is created by
introducing impurity elements that have
five valence electrons (pentavalent), such
as antimony, arsenic, and phosphorus.
•
Phosphorus or arsenic are the materials
added to create an N-type semiconductor.
These have five electrons in their outer
orbital; the crystal has four. This means that
one electron doesn't have anything to bond
with, so it moves around freely, increasing
the flow of electrical current through the
silicon.
The p-type material is formed by doping
a with impurity atoms having three
valence electrons(trivalent) such as
boron, gallium, and indium.
•
1.
2.
3.
4.
5.
There are two types of processes that follow after the formation of a p-n junction –
• diffusion and
• drift.
diffusion is the process that follows the flow of particles from higher concentration to lower
concentration, due to difference in the concentration of electrons and holes at the two sides of a
junction, the electrons from the n-side diffuse to the p-side and the holes from the p-side
diffuse to the n-side. this leads to raise in diffusion current.
Also, there is an ionized donor is left behind on the n-side, which is an immobile charge this
develop when an electron diffuses from the n-side to the p-side. As the result of this process, a
layer of positive charge is developed on the n-side of the junction.
Similarly, an ionized acceptor is left behind in the p-side when a hole goes from the p-side to
the n-side, resulting in the formation of a layer of negative charges in the p-side of the
junction. This region of negative (-) and positive charge (+) on either side of the junction is
termed the depletion region.
An electric field direction from a positive charge towards the negative charge is developed,
Due to this positive charge region on either side of the junction, Due to this electric field, the
flow of electrons and holes takes place. This is termed the drift motion. generally, the direction
of the drift current is opposite to that of the diffusion current.
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or
•
At the instant of pn-junction formation, the free electrons near the junction in the n region begin
to diffuse across the junction into the p region where they combine with holes near the junction.
•
As a result, n region loses free electrons and this creates a layer of positive charges (pentavalent
ions) near the junction.
•
As the electrons move across the junction, the p region loses holes as the electrons and holes
combine. The result is that there is a layer of negative charges (trivalent ions) near the junction.
•
These two layers of positive and negative charges form the depletion region or depletion layer.
•
The term depletion is due to the fact that near the junction, the region is depleted, i.e., emptied of
charge carriers (free electrons and holes) due to diffusion across the junction.
•
The depletion layer is formed very quickly and is very thin as compared to the n region and the p
region.
•
Once pn junction is formed and depletion layer is created, the diffusion of free electrons stops.
•
In other words, the depletion layer acts as a barrier to the further movement of free electrons
across the junction.
•
The positive and negative charges set up an electric field which acts as a barrier to the free
electrons in the n region. This is shown in fig.
There exists a potential difference across the
depletion layer known as barrier potential (VO).
The typical barrier potential is approximately:
For silicon. V0-0.7 V.
for germanium, VO™ 0.3 V.
➢ With a neat diagram explain the working of a PN-junction diode under No bias,
Reverse bias and forward bias.
the diode is a two-terminal device, the application of a voltage across its
terminals leave three possibilities:
1. No bias (VD = 0 V),
2. Forward bias (VD > 0 V), and
3. Reverse bias (VD < 0 V).
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Zero Bias (No Bias):
• When the P-N junction diode is in zero bias condition, there is no external voltage
applied and this means that the potential barrier at the junction does not allow the
flow of current.
• Therefore, the circuit current is zero at V=0 V, as indicate by the point O in the
graph.
➢ With a neat diagram explain the working of a PN-junction diode under forward
bias. (3m) (6)
Forward bias
• When external D.C. voltage applied to the junction is in such a direction that it
cancels the potential barrier, thus permitting current flow, it is called forward
biasing.
• To apply forward bias, the positive terminal of the battery is connected to p-type
and negative terminal is connected to n type of the pn-junction as shown in fig.
• As potential barrier voltage is very small (0.1 to 0.3 V), therefore, a small forward
voltage is sufficient to completely eliminate the barrier.
•
•
the potential barrier at the junction decreases, allowing the majority carriers (electrons in n-type
and holes in p-type) to move across the junction and recombine with the opposite type carriers in
the depletion region.
This results in a reduction in the width of the depletion region and an increase in the current flow
through the diode.
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• In this condition, the potential barrier height is reduced, and the depletion region
becomes narrower.
• This reduces the resistance of the diode, and the current can flow easily. Therefore,
a large forward current flows through the diode.
• Once the barrier is eliminated by the forward voltage, junction resistance becomes
almost zero and a low resistance path is established for the entire circuit.
Therefore, current flows in the circuit. This is called forward current.
•
•
•
•
•
•
current-voltage characteristics of a PN-junction diode are nonlinear, which means that the current
flowing through the diode does not increase linearly with the applied voltage.
forward voltage i.e., 0.7 V for Si and 0.3 V for Ge,
this instant onwards the current increases with the increase in forward voltage. Hence the curve
OB obtained with forward bias.
From the forward characteristics, it can be noted that at first i.e., region OA, the current increases
very slowly and the curve is non-linear. It is because in this region the external voltage applied to
the pn junction is used in overcoming the potential barrier.
However, once the external voltage exceeds the potential barrier voltage, the potential barrier is
eliminated and the pn junction behaves as an ordinary conductor.
Hence, the curve AB raises very sharply with the increase in external voltage and the curve are
almost linear.
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Reverse Bias
• When the external DC voltage applied to the junction is in such a direction that
potential barrier is increased, it is called reverse biasing.
• To apply reverse bias, the positive terminal of the battery is connected to n-type
and negative terminal to p-type of the pn junction as shown in fig.
• The applied reverse voltage establishes an electric field which acts in the same
direction as the field due to potential barrier.
• Therefore, the resultant field at the junction is strengthened and the potential
barrier height is increased as shown in fig.
• The increased potential barrier prevents the flow of charge carriers across the
junction.
• Thus, a high resistance path is established for the entire circuit and hence the
current does not flow.
• However, a very small current of the order of μA, flows through the circuit in
practice.
• This is knowing as reverse saturation current (IS) and it is due to the minority
carriers in the junction.
•
•
•
•
As we already know, there are few free electrons in p-type material and few holes in n-type
material. These free electrons in p-type and holes in n-type are called minority carriers.
The reverse bias applied to the pn junction acts as forward bias to their minority carriers and
hence, small current flows in the reverse direction.
If the applied reverse voltage is increased continuously, the kinetic energy of the minority
carriers may become high enough to knock out electrons from the semiconductor atom.
At this stage breakdown of the junction may occur. This is characterized by a sudden increase of
reverse current and a sudden fall of the resistance of barrier region. This may destroy the junction
permanently.
Siri- 7
➢ Explain forward and reverse characteristics of a semiconductor diode (5)
Forward semiconductor diode
Connecting positive terminal of voltage
supply to ‘p’ and negative terminal to ‘n’
diminishes the potential barrier
Anode voltage > cathode voltage
It has significant forward current
Depletion layer is thinner
Decrease the diode resistance
permit the current to flow through the diode.
current levels are dependent on the forward
voltage
a device functions as a conductor
Reverse semiconductor diode
Connecting positive terminal of voltage
supply to ‘n’ and negative terminal to ‘p’
Strengthen the potential barrier
Anode voltage < cathode voltage
has a marginal forward current,
Depletion layer is Thicker
Increases the diode resistance
does not permit the current to flow
Current is negligible or minimal
a device functions as an insulator
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➢ Draw the variation of forward current with respect to the forward voltage for both
Si and Ge diodes.
➢ Draw the VI characteristics of a regular Si diode and mark the parameters on it.
(3m)
• The primary difference between silicon and germanium diodes is the voltage
needed for the diode to turn on (or become “forward-biased”).
• Silicon diodes require 0.7 volts to become forward-biased,
• Whereas germanium diodes require only 0.3 volts to become forward-biased.
Siri- 9
➢ Explain why the diode current is less before the break down and high after
breakdown (4)
Before breakdown:
• Diode behaves as an insulator in the reverse direction
• Only a very small current, known as the reverse saturation current, can flow
• Depletion region acts as a barrier to the flow of current
After breakdown:
• Depletion region breaks down
• A large current can flow through the diode in the reverse direction
• Breakdown causes the depletion region to become conductive
• Significant number of charge carriers are able to flow through the depletion region
• Diode current is high after breakdown
Before breakdown:
• Diode is forward-biased, allowing current to flow through
• Current through the diode is limited by its forward resistance
• Voltage drop across the diode is small
• Current increases exponentially with applied voltage
After breakdown:
• Diode begins to conduct heavily in the forward direction
• Current through the diode increases significantly
• Breakdown voltage is reached due to excessive electric field
• Free charge carriers are created that can conduct current through the diode
• Diode current is high after breakdown
Semiconductor Diode – Forward & Reverse Characteristics
Knee voltage (Vk) is also known as cut in
voltage. The minimum amount of voltage
threshold inspections required for
conducting the diode is known as knee
voltage or cut in voltage.
The forward voltage at which the current
through PN junction starts increasing
rapidly is known as knee voltage.
Siri- 10
➢ Explain the V-I characteristics of the diode using Shockley’s equation.
➢ Draw the characteristics of forward bias and explain the working with the help of
diode equation (3)
The Shockley diode equation, also known as the diode current equation (diode law), is
the I–V characteristic of a diode in either forward or reverse bias (applied voltage).
ID = IS(𝑒
𝑉𝐷
𝑛𝑉𝑇
-1)
Where,ID= diode current,
IS = leakge or reverse bias saturation current
VD = diode voltage,
VT = thermal voltage= kT/q
n = ideality factor or emission coefficient
q=Electron Charge: 1.6022x10-19 Columb (C)
T=absolute temp in Kelvin (K=273+°C )
k=Boltzmann’s Constant : 1.3806x10-23 J/K
• for a forward bias, VD is positive, hence exponential index has positive sign. Due
to this 1<< 𝑒
𝑉𝐷
𝑛𝑉𝑇
ID = IS 𝑒
, hence neglecting 1
𝑉𝐷
𝑛𝑉𝑇
this indicates once bias voltage exceeds cut in voltage, the forward current
increases exponentially.
• In reverse biased condition, VD is negative. hence exponential index has negative
sign, which is << 1, hence neglecting exponential term,
ID = - Is
This indicates, it flows in opposite direction to that of forward current and almost
constant, which is simply the horizontal line.
• The diode current equation takes its form when we have the diode operating at room
Siri- 11
➢ Explain the effect of temperature on the following i) Knee voltage ii) Reverse
saturation current iii) Breakdown voltage
➢ Explain the effect of temperature on the VI characteristics of diode. Show this
graphically for two different temperatures. (6m) (6m)
The Effect of variation in temperature across a semiconductor diode is observed both
in the forward as well as in reverse characteristics
• Rise in temperature generates more electron-hole pair thus conductivity increases
and thus increases in current
• PN junction diode parameters like
▪ Reverse saturation current,
▪ Reverse breakdown voltage
▪ Bias current,
▪ Barrier voltage
are dependent on temperature.
• Increase in the temperature increases carrier concentration. As a result, knee
voltage & breakdown voltage decreases while reverse saturation current increases.
• Under Forward Bias the Change in Temperature across the diode:
Barrier voltage is dependent on temperature hence it decreases by 2.5mV/1ºC for
rise in temperature for both germanium and silicon.
• Under Reverse Bias the Change in Temperature across the diode:
Reverse saturation current (IS) of diode increases with increase in the temperature
the rise is 7%/1ºC for both germanium and silicon and approximately doubles for
every 10ºC rise in temperature.
• Reverse breakdown voltage (VR) also increases as the temperature increases.
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•
•
The reverse saturation current Is will just about double in magnitude for every 10°C increase in
temperature.
Knee voltage shift left at a rate of 2.5mV per centigrade degree increase in temperature.
➢ Name the three types of resistance associated with diodes (3)
Resistance of a Semiconductor Diode
1. FORWAD RESISTANCE: An actual diode offers a very small resistance (not zero)
when forward biased and is called a forward resistance (r it acts as a perfect
conductor)
2. REVERSE RESISTANCE: diode offers a very high resistance (not infinite) when
reverse biased and is called as a reverse resistance (r it acts as a perfect insulator)
Type of applied voltage or signal will define the following resistance levels
• DC or Static Resistance
• AC or Dynamic Resistance
• Average AC Resistance
Siri- 13
➢ Explain the following forward resistances in diode: (i) DC Resistance (ii) AC
Resistance (iii) Average AC Resistance.
➢ Explain the difference between AC resistance and Dynamic AC resistance of a
diode. From Shockley’s equation, derive the expression for the AC resistance of the
diode.
➢ Define AC resistance and Dc resistance of a diode (3)
➢ Explain the difference between Ac resistance and average Ac resistance (3m) (3m)
Static Resistance or DC resistance: the resistance offered by a p-n junction diode
when it is connected to a DC circuit is called static resistance.
Rf =
𝐷𝐶 𝑉𝑜𝑙𝑡𝑎𝑔𝑒
𝐷𝐶 𝐶𝑢𝑟𝑟𝑒𝑛𝑡
It is clear from the graph that for the
operating point P, the forward voltage is
OA and the corresponding forward
current is OB. Therefore, the static
forward resistance of the diode is given
as
𝑂𝐴
Rf =
𝑂𝐵
Forward bias: 10 Ω to 80 Ω
Reverse Bias: 10 MΩ
Dynamic Resistance or AC resistance: the resistance offered by a p-n junction diode
when it is connected to an AC circuit is called dynamic resistance.
AC or Dynamic Resistance: The derivative of a function at a point is equal to the slope of the tangent line
drawn at that point
rf =
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑉𝑜𝑙𝑡𝑎𝑔𝑒
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝐶𝑢𝑟𝑟𝑒𝑛𝑡
=
𝐶𝐸
𝐷𝐹
=
∆𝑉
∆𝐼
From the figure A above it is clear that for an operating point P the AC forward resistance is
determined by varying the forward voltage (CE) on both sides of the operating point equally and
measuring the corresponding forward current (DF).
Dynamic resistance can be found simply by substituting the quiescent value of the diode current into
the equation also
26𝑚𝑉
Typically, the ac resistance of a diode in the
rf =
active region will range from 1 Ω -100 Ω.
𝐼
r’f
=
26𝑚𝑉
+ rb ohms
𝐼
where rb is body resistance
The value of reverse resistance is very large as
compared to forward resistance.
The ratio of reverse to forward resistance is
100000:1 for silicon diodes,
whereas it is 40000:1 for germanium diode.
Siri- 14
➢ Derive the expression for dynamic resistance of the diode. (3m)
➢ From Shockley’s equation, derive the expression for the Ac resistance of the diode.
(3m) (3m) (3m)
➢ Is derived ac resistance is equal to that obtained graphically? Justify (2)
ID = IS(𝑒
𝑉𝐷
𝑛𝑉𝑇
-1)
Average AC Resistance:
If applied input signal is sufficiently large to produce a broad swing and the resistance
determined by a straight line drawn between the two intersections established by the
maximum and minimum values of input voltage is called Average AC Resistance.
Siri- 15
➢ Explain the difference between Ac resistance and average Ac resistance (3m)
➢ Explain the different types of breakdown that occur in diodes.
➢ Explain the characteristics of Avalanche breakdown and Zener breakdown (5)(2)
Avalanche breakdown: is a phenomenon that can occur in a diode when a reverse
bias voltage is applied that is higher than the diode's breakdown voltage.
• In the reverse bias condition, the electric field across the depletion region of the
diode increases, causing free charge carriers such as electrons and holes to gain
kinetic energy and velocity.
• The high energy carriers can collide with other atomic structures in the material,
causing covalent bonds to break and releasing more free charge carriers.
• This chain reaction of ionization is known as avalanche multiplication (ionization
process.), which can lead to a rapid increase in current through the diode and
ultimately cause the diode to fail.
Siri- 16
Zener breakdown:
• Zener break down occurs when both P and N type material are heavily doped in a
semiconductor diode.
• Hence the depletion layer region is narrow down.
• When a small reverse bias voltage is applied across a diode a very strong electric
field is produced.
• Due to this electric filed, covalent bond breaks and produces large number of free
charge carriers.
• The generated carriers can themselves collide with other atoms and generate even
more carriers, results in a sudden increase in reverse current.
• This breakdown phenomenon is known as Zener breakdown, and it occurs at a
lower voltage than avalanche breakdown.
➢ Explain the three models of a diode with the help of VI characteristics and
equivalent circuits.
➢ Explain piece wise linear model and ideal equivalent circuit of a diode with the help
of its equivalent circuit and VI characteristics (5)
➢ Explain first and second diode approximations (2)
Diode Equivalent Diagrams/Diode Approximations:
Diode approximation is a mathematical method used to approximate the nonlinear
behavior of real diodes to enable calculations and circuit analysis.
There are three different approximations used to analyze the diode circuits, namely
I.
First Approximation (Ideal Diode Characteristics)
II.
Second Approximation (Simplified Diode Characteristics)
III. Third approximation (Linear Piece-wise Diode Characteristics)
Siri- 17
Ideal diode Characteristics:
first approximation method, the diode is considered as
• A forward-biased diode and as a closed switch with zero voltage drops and
• Reverse biased diode as an open switch.
Simplified Diode Characteristics:
In the second approximation, the diode is considered as
• a forward-biased diode in series with a battery to turn on the device.
o For a silicon diode to turn on, it needs 0.7V.
o A voltage of 0.7V or greater is fed to turn on the forward-biased diode.
o The diode turns off if the voltage is less than 0.7V.
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Linear Piece-Wise Diode Characteristics:
➢ Draw piece wise linear (PWL)model of a diode and its equivalent circuit (3)
• The third approximation of a diode includes voltage across the diode and voltage
across bulk resistance, RB .
• The voltage drop across the diode is calculated using the formula Vd = 0.7V + Id *RB
➢ What is the difference between the characteristics of a simple switch and that of a
practical diode?
Simple switch:
•
•
•
•
Can be either open or closed, allowing
or blocking the flow of current.
Has little or no voltage drop when
closed.
Can be opened or closed quickly, with
no delay in response.
Not designed to handle reverse
voltage.
Practical diode:
•
•
•
•
Conducts current in one direction and blocks it in
the opposite direction.
Has a characteristic voltage drop across it when
conducting current in the forward direction.
Has a finite response time due to physical
processes.
Can handle reverse voltage up to a certain limit,
beyond which it can break down and allow
current to flow in the reverse direction.
➢ Using Second Approximation equivalent circuit explain the working of Parallel diode configuration
when Two Si diodes are connected in parallel with a Voltage Source with Series Resistance?
• The equivalent circuit consists of two diodes in parallel, each with a series resistance.
• The voltage source is connected across the parallel combination.
• The total current flowing through the circuit is the sum of the current flowing through each
diode.
• As the voltage across the diodes increases, they begin to conduct current.
• The voltage drop across the series resistances also increases, causing a reduction in the voltage
across the diodes.
• The resistance of each diode increases as the voltage across it decreases, causing a reduction in
the current flowing through it.
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•
•
•
This process continues until the voltage across the diodes is equalized, and the current flowing
through each diode is the same.
The two diodes share the current flowing through the circuit, which helps to distribute the power
dissipation evenly between them.
The series resistance limits the current flowing through the diodes to prevent damage to the
components.
➢ Define Logical Operations and types of Basic Logical operations
Logical operations: It is an operation that acts on binary numbers to produce a result
according to the Laws of Boolean Logic.
Basic Logical operations: AND gate, OR gate, NOT gate
➢ Explain logical OR gate operation using diode (2)
OR gate:
• An OR gate may also have two or more inputs but produce only one output.
• The OR gate produces an output of logic 1 state even if any of its inputs is in logic
1 state and also produces an output of logic 0 state if any of its inputs is in logic 0
state.
• The OR gate performs logic addition, more commonly known as the OR function
• In OR gate, output voltage is high if any one or all of the input voltages are high.
OR Gate Symbol
The symbols used for OR gates with 2, 3 and N inputs are shown in Fig 1 (a), (b) and
(c) respectively.
• The inputs A, B, C…N are logic voltage levels and the output Z is a logic voltage
level whose values is the result of the OR operation on A, B, C ….and N.
• the OR gate operates in such a way that its output is one or more inputs are high.
• The OR gate output will be at logic o.
• Its logic equation is given as: Z = A OR B OR C ….OR N
Z = A + B + C +…………..+N
• The above equation is known as Boolean equation or the logical equation of the
OR gate.
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OR Gate Truth Table
The logical operation of two-input and three table 1 and table 2 respectively.
The truth table can be expanded for any number of inputs; but regardless of the
number of inputs, the output is high when any one or more of the inputs are high.
➢ With neat diagram and truth table explain logical AND gate operation using diode
(5)
AND gate:
• The AND gate performs logical multiplication, more commonly known as AND
function.
• The AND gate provides high output only when all inputs are high.
• The AND gate has two or more inputs and a single output, as shown in the standard
logic in fig 1 (a, b & c).
•
Z = A AND B AND C …AND n = A.B.C…….n = ABC….n
Truth Table of AND Gate
The logical operation of the 2-input and 3 table 1 and table 2 respectively.
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➢ Realize Logical OR Operations using Diodes
OR Gate can be realized using Diodes as discussed below.
DIODE OR GATE: Diodes may be used to build an OR gate, as shown in the Fig
• If input voltages at points A, B are low then all diode are non-conducting so output
voltage, Vout is low.
• But if any of the input terminals is at high voltage, then diode connected with that
particular terminal is forward biased and current flows through the resistance R.
• The result is that Vout is at high level.
➢ Realize AND Operation using Diodes (5)
The fig. shows one way to build a 2-input AND gate using diodes
AND Gate can be realized using Diodes as discussed below.
DIODE AND GATE:
• The input voltages are labeled A and B, while the output voltage Z.
• When voltages of both inputs are high, both the diodes are non-conducting because
the diodes are reverse-biased. Since the diodes are off, no current flows through
resistor R, and the output is pulled up to the supply voltage Vcc (+5). Thus, for
both inputs high, output is high.
• But when input voltage of either or both terminals are low, cathode(s) of the
diode(s) connected to low input terminal(s) is/are grounded and the diode(s)
become(s) forward-biased, resulting in flow of current through resistor R. So, in
such a condition, voltage of the output terminal becomes low.
Siri- 22
Mcq:
1. A semiconductor has generally ___________ Valence electronics.
2
3
4
5
2) Addition of pentavalent impurity to a semiconductor creates many ____________.
Free electrons
Holes
Valence electrons
Bound electrons
3)An n-type semiconductor is ______________
Positively charged
Negatively charged
Electrically neutral
None of the above
4)When a pure semiconductor is heated, its resistance ___________.
Increases
decreases
Remains the same
cannot say
5) In the p & n regions of a diode the _________ & the ___________ are the minority charge carriers
respectively.
holes, holes
electrons, electrons
holes, electrons
electrons, holes
1. In a PN junction the potential barrier is due to the charges on either side of the junction, these charges
are ______________.
a) Majority carriers
c) Both (a) and (b)
b) Minority carriers
d) Fixed donor and acceptor ions
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2) When the graph between current through and voltage across a device is a straight line, the device is
referred to as ______________.
Linear
Active
Nonlinear
Passive
3) For a PN junction diode, the current in reverse bias may be ___________.
Few milli amperes
Between 0.2 A and 15
A Few amperes
Few micro or nano amperes
4) In a PN junction with no external voltage, the electric field between acceptor and donor ions is called
Peak
Barrier
Threshold
Path
5) Choose the CORRECT Statement In an unbiased PN junction.
The junction current is due to minority carriers only
The junction current at equilibrium is zero as equal but opposite carriers are crossing the junction
The junction current reduces with rise in temperature
The junction current at equilibrium is zero as charges do not cross the junction
1. What will be the thermal voltage of the diode if the temperature is 300K?
25.8 mV
50 mV
50V
9.627 mV
o
2) What is the value of the voltage equivalent of temperature at room temperature (27 C)?
26mV
0.26mV
36mV
260mV
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3) The diode current equation is not applicable in __________.
Forward biased state
Reverse biased state
Unbiased state
It is applicable in all bias states
4) In the diode volt ampere characteristics what will be the resistance if a slope is drawn between the
voltages 50 to 100 and corresponding current 5 to 10.
5 ohms
10 ohms
50 ohms
100 ohms
5)What happens to cut-in voltage when the temperature increases?
Cut-in voltage increases
Cut-in voltage decreases
Cut-in voltage either increases or decreases
Cut-in voltage doesn't depend on temperature.
1. Which of the following are true about a Zener diode?
1) it allows current flow in reverse direction also
2) it is used as a shunt regulator
3) it operates in forward bias condition only
3 only
1 and 2
2 and 3
2 only
2) Choose the Correct Statement
In Diode Forward bias is established by applying the positive potential to P-type material and negative
potential to n-type material
In Diode Forward bias is established by applying the negative potential to P-type material and Positive potential to
n-type material.
In a diode the flow of current through it is due to the Minority Charge Carriers only
In Diode Reverse bias is established by applying the positive potential to P-type material and negative potential to
n-type material.
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3) In the breakdown region, a Zener diode behaves like a _________________source.
a) Constant voltage
b) Constant current
c) Constant resistance
d) None of the above
4)Identify the Characteristics of Diode Equivalent Circuit
(i) Ideal (ii) Simplified Model
(i) Ideal (ii) Piecewise-linear model
(i) Piecewise-linear model (ii) Simplified Model
(i) Ideal (ii) Piecewise-linear model
5)A Zener diode works on the principle of _________.
tunneling of charge carriers across the junction
thermionic emission.
diffusion of charge carriers across the junction
hopping of charge carriers across the junction
1. Find the current I in room temperature if both diodes are identical. Voltage V = 0.8V and let the
reverse saturation current be 10-9A.
a) 4.8mA
b) 3.2mA
c) 2.5mA
d) 7mA
2) What will be the current I in the circuit diagram below. Take terminal voltage of diode as 0.7V and
I0as 10-12A.
a) 2.3mA
b) 0.9mA
c) 1mA
d) 4mA
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3) The input voltage V1 of the circuit is 2V and resistor if 1K ohm. The cut-in voltage of the silicon
diode is 0.7V and the reverse saturation current is 10-8A. The temperature at which diode operates is
30°C. The voltage across resistor when diode starts conducting is ______________________.
A. 0.7V
B. 1.3V
C. 0.3V
D. 2 V
4) Find Diode Current ID and Voltage across the Resistance VR for the following circuits
(i) 3.32mA (ii) 3.32mA
(i) 0A (ii) 3.32mA
(i) 1mA (ii) 3.32mA
(i) 0A (ii) 2.32mA
5) In a series Diode Configuration If diode is reverse biased when Voltage Vis 5V and resistance R is
5K ohm and the cut-in voltage of the diode is 0.7V, what will be the voltage Voutacross the diode?
Consider reverse saturation current as 10-8A and operating temperature as 25°C.
0V
-4.5V
-5V
-3.2V
1. When two diodes Ge and GaAs are connected in parallel for circuit gets locked to __________
voltage during forward bias condition
a) 0.7V
b)0.3V
c)1.0V
d)1.2V
2) When two diodes Si and GaAs are connected in parallel the circuit gets locked to __________ voltage
during forward bias condition.
a) 0.7V
b)0.3V
c)1.0V
d)1.2V
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3) When two diodes Si and Ge are connected in parallel circuit gets locked to __________ voltage
during forward bias condition.
a) 0.7V
b)0.3V
c)1.0V
d)1.2V
4) When two diodes Si and Ge are connected in parallel circuit gets locked to __________ voltage
during Reverse bias condition.
a) 0.7V
b)0.3V
c)1.0V
d)None of the above
1. Reverse biased condition of a diode in piecewise linear model is equivalent to __________
a) Resistor
b) Capacitor
c) Conductor
d) Insulator
2) Which of the following statements best describes the reason for not using diodes to implement logic
gates?
a) Diodes are expensive
b) Diodes are unreliable and less efficient
c) The diode circuits have limited range of operation
d) Diodes are bulky for a logic gate
3) What is the logic gate implemented in the following circuit?
a) OR
b) AND
c) NOT
d) NOR
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4) What is the logic gate implemented in the following circuit?
a) OR
b) AND
c) NOT
d) NOR
1. Thermal voltage Vth is given by
a. Vth=kT/q
b. Vth=qT/k
c Vth=kq/T
d. Vth=k/q
2) The depletion region of PN junction is one, that is depleted of
a. Atoms
b. Mobiles charges
c. Immobile charges
d. Velocity of the carriers
3) For a reverse biased PN junction, the current through the junction increases abruptly at
Breakdown voltage
0V
0.2 eV
7.2 eV
0
0
4) If Reverse Saturation current at 27 Cis 23nA find the current at 32 C.
A. 12.34nA
B. 23.56nA
C. 17.45nA
D. 32.52nA
o
5) The Reverse saturation current of a Si diode is 2pA at 37 C. Determine the Thermal and forward
biased voltage across the diode if the forward current through the diode is 1.52 A.
A. VT=26.73V VD=0.73V
B. VT=25.73V VD=0.63V
C. VT=24.73V VD=0.33V
D. VT=24.73V VD=0.53V
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1. As temperature is increased, the knee voltage across a diode
(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase and decrease depending upon the doping levels in the junction.
o
2) The knee voltage of a Si diode is 0.68V and its reverse saturation current is 15nA at 25 C. Determine
these values at 40oC.
A. VD= 0.6125 V and IS=41.42nAB
B.VD= 0.6425 V and IS=42.42nA
C. VD= 0.6225 V and IS=42.42nA
D. VD= 0.6325 V and IS=41.42nA.
o
3) How much times reverse saturation current will increase if temperature increases 15 C?
a) 2.52
c) 4.12
b) 4.62
d) 2.82
1. Diode DC resistance is also known as
a) Static
b) Dynamic
c) Average
d) None of the above
2) For the given ID find the dynamic Resistance in ohms.
i) ID= 20 mA , at 27OCtemperature . ii)ID= 20 mA at 57OCtemperature.
A. i) 1.23 ii)1.22
B. . i) 1.30 ii)1.42
C. . i) 1.11 ii)1.32
D. . i) 1.30 ii)1.12
3) Statement-1: Piecewise linear model is generally not used for diode analysis.
Statement-2: The value of Rav is negligible as compared to the load resistance.
Which of the following holds true?
a) Statement-1 is true, Statement-2 is true and Statement-2 is a proper explanation for Statement-1
b) Statement-1 is true, Statement-2 is true and Statement-2 is not a proper explanation for Statement-1
c) Statement-1 is true, Statement-2 is false
d) Statement-1 is false, Statement-2 is true
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4) Determine the Average Ac Resistance from the graph.
A. 50 ohm
B.150ohm
C.300ohm
D.450ohm
Numericals
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