2.A.

Explain the working of PN Junction diode with Forward biased

and reversed biased condition .
Answer :-
PN Junction Diode :-
* A PN junction diode is formed by joining a P-type semiconductor
(rich in holes) and an N-type semiconductor (rich in electrons).
* At the junction, electrons from the N-side diffuse into the P-
side, and holes from the P-side diffuse into the N-side.
* This diffusion creates a depletion region, a zone devoid of free
charge carriers, and an electric field across the junction.
* The electric field across this region creates a potential barrier.
. Forward Bias:-
* Connection: The positive terminal of a voltage source is
connected to the P-side, and the negative terminal to the N-side.
* Effect: The applied voltage opposes the built-in potential
barrier.
* Mechanism:
* As the forward voltage increases, the depletion region
narrows.
* When the forward voltage exceeds the barrier potential
(approximately 0.7V for silicon and 0.3V for germanium), the
depletion region collapses.
* Electrons from the N-side are injected into the P-side, and
holes from the P-side are injected into the N-side.
 * A significant current flows through the diode.
* Current flow: The current increases exponentially with the
increase in forward voltage.
* Characteristics: In forward bias, the diode acts as a low
resistance path, allowing substantial current flow.

3. Reverse Bias:
* Connection: The positive terminal of a voltage source is
connected to the N-side, and the negative terminal to the P-side.
* Effect: The applied voltage reinforces the built-in potential
barrier.
* Mechanism:
* The applied voltage pulls the holes away from the junction in
the P-side and the electrons away from the junction in the N-side.
* This widens the depletion region, increasing the potential
barrier.
* Only a very small leakage current (reverse saturation current)
flows due to minority carriers.
 * Current flow: The current is extremely small and remains
relatively constant with increasing reverse voltage until the
breakdown voltage is reached.
* Characteristics: In reverse bias, the diode acts as a high
resistance path, blocking current flow.
* Breakdown: If the reverse voltage exceeds the breakdown
voltage, a large current flows due to avalanche or Zener
breakdown. This can damage the diode.

2b.Differentiate between Zener avalanche breakdow breakdown

Zener Breakdown:
* Mechanism:
* Zener breakdown occurs due to a strong electric field across
the PN junction. This intense field pulls electrons directly from
the valence band to the conduction band, effectively “tunneling"
them across the narrow depletion region.
* Essentially, the electric field is so strong that it breaks the
covalent bonds holding the atoms together.
* Doping:
 * It occurs in heavily doped PN junctions, resulting in a very thin
depletion region.
* Voltage:
* Typically occurs at lower reverse bias voltages.
* Temperature Coefficient:
* Has a negative temperature coefficient, meaning the
breakdown voltage decreases as temperature increases.
* Characteristics:
* Sharp, well-defined breakdown voltage.
Avalanche Breakdown:
* Mechanism:
* Avalanche breakdown happens when minority carriers
(electrons or holes) are accelerated by a strong electric field
within the depletion region.
* These accelerated carriers collide with other atoms, ionizing
them and generating more electron-hole pairs. This creates a
chain reaction, or "avalanche," of charge carriers.
* Doping:
* It occurs in lightly doped PN junctions, where the depletion
region is wider.
* Voltage:
* Typically occurs at higher reverse bias voltages.
* Temperature Coefficient:
 * Has a positive temperature coefficient, meaning the
breakdown voltage increases as temperature increases.
* Characteristics:
* The breakdown characteristic is less sharp compared to Zener
breakdown.
Key Distinctions Summarized:
* Doping level: Zener breakdown occurs in heavily doped
junctions, while avalanche breakdown occurs in lightly doped
junctions.
* Depletion region: Zener breakdown has a thin depletion region,
and avalanche breakdown has a wider one.
* Mechanism: Zener breakdown is due to electron tunneling, and
avalanche breakdown is due to impact ionization.
* Voltage: Zener breakdown occurs at lower voltages, and
avalanche breakdown at higher voltages.
* Temperature coefficient: Zener breakdown has a negative
temperature coefficient, and avalanche breakdown has a positive
one.
In essence, Zener breakdown is a direct field effect, while
avalanche breakdown is a collision-induced effect.

3a) Compare common base and common configurations BIT

emitter with reference input gain’t and Current gain.
Answer:-
Common Base (CB) Configuration:
Input: The input signal is applied between the emitter and base,
with the base acting as the common terminal.
Output: The output signal is taken from the collector and base.
Current Gain: The current gain (alpha) is less than unity, meaning
the output current is less than the input current.
Voltage Gain: The CB configuration provides high voltage gain.
Applications: Suitable for impedance matching and RF amplifier
circuits.
Common Emitter (CE) Configuration:
Input: The input signal is applied between the base and emitter,
with the emitter acting as the common terminal.
Output: The output signal is taken from the collector and emitter.
Current Gain: The current gain (beta) is greater than unity,
meaning the output current is greater than the input current.
Voltage Gain: The CE configuration provides both current and
voltage gain, making it suitable for amplification applications.
Applications: Commonly used for amplification applications.

3b) Explain the of MOSFET. Working of enhancement type

Answer :-enhancement-type MOSFET involves grasping how
voltage applied to the gate terminal controls the flow of current
between the source and drain. Here’s a breakdown:
Basic Concepts:
* MOSFET:
* MOSFET stands for Metal-Oxide-Semiconductor Field-Effect
Transistor.
* It’s a voltage-controlled device used for switching or
amplifying electronic signals.
* Enhancement-Type MOSFET:
* In this type, a channel between the source and drain is not
initially present.
* The channel is “enhanced” or created by applying a voltage to
the gate.
Key Components:
* Source (S): The terminal where charge carriers enter the
channel.
* Drain (D): The terminal where charge carriers exit the channel.
* Gate (G): An insulated terminal that controls the channel
formation.
* Substrate (Body): The underlying semiconductor material.
* Oxide Layer (SiO2): An insulating layer between the gate and the
substrate.
Working Principle:
* No Gate Voltage (VGS = 0):
 * In an enhancement-type MOSFET, there’s no inherent channel
between the source and drain.
* Therefore, no current flows when the gate voltage (VGS) is zero.
* The device is in the “off” state.
* Applying Gate Voltage (VGS > Threshold Voltage):
* When a positive voltage (for an n-channel MOSFET) is applied
to the gate, an electric field is created.
* This electric field repels holes (in a p-type substrate) and
attracts electrons, forming an “inversion layer” or channel of
electrons beneath the oxide layer.
* The minimum gate voltage required to create this channel is
called the threshold voltage (Vth).
* As Vgs increases past Vth, the strength of the channel
increases, and therefore the amount of current that can flow from
the drain to the source increases.
* Current Flow:
* Once the channel is formed, applying a voltage between the
drain and source (VDS) causes current to flow through the
channel.
* The amount of current flowing is controlled by the gate voltage
(VGS). A higher VGS results in a stronger channel and more
current.
Key Characteristics:
* Normally off: It doesn’t conduct current when VGS = 0.
* Voltage-controlled: The gate voltage controls the channel
conductivity.
* Widely used in digital circuits due to its switching capabilities.
In essence, the enhancement MOSFET “enhances” the
conductivity between the source and drain by creating a channel
when a suitable gate voltage is applied.
4 a )With Neat diagram of Op-Amp block. Diagram, explain its in
an ideal characteristics Op-Amp.
Answer:- An operational amplifier (op-amp) is a high-gain
differential amplifier with two input terminals:
* Inverting input (-): Input signals applied to this terminal produce
an output signal with opposite polarity.
* Non-inverting input (+): Input signals applied to this terminal
produce an output signal with the same polarity.
Block Diagram:

Ideal Characteristics of an Op-Amp:

* Infinite Input Impedance:
* An ideal op-amp draws no current at its input terminals.
* This means that the input impedance is infinitely high,
preventing any loading effect on the signal source.
* Zero Output Impedance:
* An ideal op-amp can deliver any amount of current to the load
without a change in output voltage.
* This implies that the output impedance is zero.
* Infinite Open-Loop Gain (Aol):
* The open-loop gain of an ideal op-amp is infinite.
* This means that even a tiny difference between the input
voltages produces a very large output voltage.
* Infinite Bandwidth:
* An ideal op-amp can amplify signals of any frequency without
any loss in gain.
* Zero Offset Voltage:
* In an ideal op-amp, the output voltage is zero when both input
terminals are grounded.
* Infinite Common-Mode Rejection Ratio (CMRR):
* An ideal op-amp completely rejects any signals that are
common to both input terminals.
These ideal characteristics are not perfectly achievable in real
op-amps, but modern op-amps come very close to these ideals,
making them versatile components in a wide range of electronic
circuits.
Key Points:
* Op-amps are widely used in analog circuits for various
applications like amplification, filtering, and signal conditioning.
* The ideal characteristics of op-amps provide a simplified model
for circuit analysis and design.
* Real op-amps have limitations compared to the ideal model,
but these limitations are often negligible in practical
applications.
By understanding the ideal characteristics and limitations of op-
amps, engineers can effectively design and analyze op-amp
circuits for various applications.

4 B) Explain Following parameters of Op-Amp :-

(a) Input offset Voltage
(b) Input offset current
(c) Slew rate
(d) CMMR
Answer:-
a) Input Offset Voltage (Vio)
* Definition:
 * The input offset voltage is the small DC voltage that must be
applied between the input terminals of an op-amp to force the
output voltage to zero.
* Ideally, when both inputs are at the same voltage, the output
should be zero. However, due to imperfections in the op-amp’s
internal circuitry, a small voltage difference is required to achieve
a zero output.
* Significance:
* It introduces DC errors in the output, especially in high-gain
applications.
* Lower input offset voltage is desirable for accurate DC
amplification.
(b) Input Offset Current (Iio)
* Definition:
* The input offset current is the difference between the DC bias
currents flowing into the two input terminals of an op-amp.
* Ideally, these bias currents should be equal, but due to
mismatches in the input transistors, a small difference exists.
* Significance:
* It can cause voltage errors when the input impedance is high.
* Lower input offset current is crucial for applications with high
source impedances.
C Slew Rate (SR) :-
* Definition:
 * The slew rate is the maximum rate of change of the output
voltage of an op-amp, expressed in volts per microsecond (V/µs).
* It indicates how quickly the op-amp can respond to a rapid
change in the input signal.
* Significance:
* It limits the op-amp’s ability to accurately reproduce high-
frequency signals.
* If the input signal changes faster than the slew rate, the output
signal will be distorted.
* This is very important in applications that deal with fast
changing signals, like audio amplifiers.
(d) Common-Mode Rejection Ratio (CMRR)
* Definition:
* The common-mode rejection ratio is the op-amp’s ability to
reject signals that are common to both input terminals.
* It’s the ratio of the differential gain (Ad) to the common-mode
gain (Ac), usually expressed in decibels (dB).
* CMRR = Ad/Ac
* Significance:
* It’s essential for rejecting unwanted noise or interference that
appears equally on both inputs.
* A high CMRR is desirable for applications where common-
mode noise is present, such as in instrumentation and
measurement systems.
 * This is very important in situations where you want to amplify
a small difference between two large signals, while ignoring the
large signal itself.
5 a) Derive of an an expression for voltage gain amplifier with
negative feedback.
Answer:-
Let’s consider a basic amplifier with negative feedback:
- A: Open-loop gain of the amplifier
- β: Feedback fraction (ratio of feedback voltage to output voltage)
- Vin: Input voltage
- Vout: Output voltage
- Vf: Feedback voltage
The output voltage (Vout) is fed back to the input through the
feedback network, which attenuates the output voltage by a
factor β.
The error voltage (Ve) is the difference between the input voltage
(Vin) and the feedback voltage (Vf):
Ve = Vin – Vf
Vout = A * Ve
Substituting the expression for Ve, we get:
Vout = A * (Vin – Vf)
Since Vf = β * Vout, we can substitute this expression into the
previous equation:
Vout = A * (Vin – β * Vout)
Rearranging the equation to solve for Vout, we get:
Vout = (A / (1 + A * β)) * Vin
Av = Vout / Vin
Substituting the expression for Vout, we get:
Av = (A / (1 + A * β)
This is the expression for the voltage gain of an amplifier with
negative feedback.
5 b) Explain the construction and work working of Crystal
oscillator with proper diagrams.
Answer :- A crystal oscillator uses a piezoelectric crystal,
typically quartz, to generate a stable and precise frequency by
exploiting its natural resonant frequency when a voltage is
applied, acting as a self-contained resonant circuit.
Construction:
Piezoelectric Crystal:
A quartz crystal is the heart of the oscillator, cut and shaped to
vibrate at a specific frequency.
Electrode:
Metal electrodes are placed on the crystal to apply an electrical
signal and sense the resulting vibrations.
Resonant Circuit:
The crystal, along with capacitors and possibly other
components, forms a resonant circuit that sustains oscillations
at the crystal’s natural frequency.
Amplifier/Inverter:
An amplifier or inverter circuit provides the necessary gain and
phase shift to maintain the oscillations.
Feedback Network:
A feedback network, often including capacitors, helps stabilize
the frequency and ensure the crystal continues to oscillate.
Working Principle:
1. Piezoelectric Effect:
When an alternating voltage is applied to the crystal, it vibrates at
its natural frequency due to the piezoelectric effect (the crystal
changes shape under an electric field).
2. Resonance:
The crystal, along with the connected components, forms a
resonant circuit that amplifies the vibrations at the crystal’s
resonant frequency.
3. Amplification and Feedback:
The amplified signal from the crystal is fed back to the input of the
amplifier, maintaining the oscillations at the crystal’s resonant
frequency.
4. Stable Frequency:
The crystal’s natural frequency provides a highly stable and
accurate clock signal.
6a )Differentiate between multiplexer and demultiplexer.
*Multiplexer (MUX):*
1. _Definition:_ A multiplexer is a digital circuit that selects one of
several input signals and forwards the selected signal to a single
output line.
2. _Function:_ Combines multiple input signals into a single
output signal.
3. _Inputs:_ Multiple input lines (e.g., 4, 8, 16).
4. _Outputs:_ Single output line.
5. _Control Signals:_ Select lines (e.g., S0, S1) to choose which
input signal to forward.
*Demultiplexer (DEMUX):*
1. _Definition:_ A demultiplexer is a digital circuit that takes a
single input signal and routes it to one of several output lines.
2. _Function:_ Distributes a single input signal to multiple output
signals.
3. _Inputs:_ Single input line.
4. _Outputs:_ Multiple output lines (e.g., 4, 8, 16).
5. _Control Signals:_ Select lines (e.g., S0, S1) to choose which
output line to route the input signal.
Key differences:
- MUX combines multiple inputs into a single output, while
DEMUX distributes a single input to multiple outputs.
- MUX has multiple input lines and a single output line, while
DEMUX has a single input line and multiple output lines.
In summary, multiplexers are used to combine multiple signals
into a single signal, while demultiplexers are used to distribute a
single signal to multiple signals.
Q6) b) Discuss the structure of the 8085 microprocessor with a
proper block diagram.
Key Components
* Accumulator (A): 8-bit register, primary register for arithmetic
and logical operations.
* ALU (Arithmetic Logic Unit): Performs arithmetic and logical
operations.
* Temporary Registers (B, C, D, E, H, L): General-purpose 8-bit
registers.
* Instruction Decoder and Machine Cycle Encoding: Interprets
instructions and generates control signals.
* Timing and Control Unit: Generates timing signals for control
and synchronization.
* Program Counter (PC): 16-bit register, holds the address of the
next instruction.
* Stack Pointer (SP): 16-bit register, holds the address of the top
of the stack.
* Address Buffer: Drives the higher order address bus (A15-A8).
* Address Latch: Holds the lower order address bus (AD7-AD0)
during the first clock cycle.
* Address/Data Buffer: Bi-directional buffer for address and data.
* Address Bus (A15-A8): Unidirectional, carries the higher order
address.
* Address/Data Bus (AD7-AD0): Bi-directional, carries the lower
order address or data.

7 write short notes

7a) Interrupt :-
* Definition: An interrupt is a signal that temporarily suspends
the current program execution to handle a specific event or
request.
* Purpose: Interrupts allow the processor to respond to real-time
events, external devices, or errors without constantly polling for
them.
* Types: Interrupts can be hardware (generated by external
devices) or software (generated by the program itself).
* Process: When an interrupt occurs, the processor saves the
current state, jumps to an interrupt service routine (ISR) to handle
the event, and then returns to the original program.
7b) Op-Amp as an Integrator :-
* Circuit: An op-amp integrator uses a capacitor in the feedback
loop.
* Function: It produces an output voltage that is proportional to
the integral of the input voltage over time.
* Application: Integrators are used in analog computers, signal
processing, and control systems.
* Formula: The output voltage (Vout) is given by:
* V_{out} = -\frac{1}{RC} \int V_{in} dt
* where R is the resistance, C is the capacitance, and Vin is the
input voltage.
7c) Clamper Circuit:-
* Function: A clamper circuit shifts the DC level of a signal
without altering its shape.
* Components: It typically consists of a capacitor, a diode, and a
resistor.
* Types: Clamping circuits can be positive or negative, depending
on the direction of the diode.
* Application: Clampers are used to restore or shift the DC level
of signals in various electronic systems.
7 d) Microcontroller :-
* Definition: A microcontroller is a small, integrated circuit that
combines a processor core, memory, and programmable
input/output peripherals.
* Purpose: It is designed for embedded systems to control
specific functions in devices.
* Features: Microcontrollers are typically low-power, cost-
effective, and have a wide range of peripherals like timers, ADCs,
and communication interfaces.
* Examples: Common microcontrollers include the Arduino Uno
(based on the ATmega328P), PIC microcontrollers, and ARM
Cortex-M series.
7e) Half-Wave Rectifier :-
* Function: A half-wave rectifier converts AC voltage into
pulsating DC voltage by allowing only one half-cycle of the AC
waveform to pass through.
* Components: It uses a single diode.
* Efficiency: The efficiency of a half-wave rectifier is low (around
40.6%).
* Application: It is used in simple power supplies and signal
processing circuits where high efficiency is not critical.