The "Electronic Devices & Circuits - Study Material" is a comprehensive and detailed PDF document designed to provide students of the Bachelor of Engineering in Computer Science program at Rajiv Gandhi Proudyogiki Vishwavidyalaya Bhopal with a comprehensive understanding of the fundamental concepts related to electronic devices and circuits. This study material covers the topics taught in Semester 3 of the program, focusing on the subject of Electronic Devices & Circuits. Content Overview: Switching Characteristics of Diode and Transistor Understanding the Turn ON and Turn OFF Time of Diodes and Transistors. Exploring the importance of Switching Characteristics in digital circuits and switching applications. Analyzing how Diodes and Transistors transition between different states during switching. Reverse Recovery Time of Diode Investigating the phenomenon of Reverse Recovery Time in diodes. Examining the implications of Reverse Recovery Time in high-frequency rectifiers and switching circuits. Understanding how charge carriers affect the transition from conducting to non-conducting state in diodes. Transistor as a Switch Utilizing transistors as electronic switches in various applications. Exploring the operation of transistors in the ON (saturation) and OFF (cutoff) states. Discussing the applications of transistor switches in digital logic circuits, amplifiers, and power control. Multivibrators Understanding the operation and applications of Bistable, Monostable, and Astable Multivibrators. Analyzing how Bistable Multivibrators can be used as memory elements and in sequential logic circuits. Exploring the application of Monostable Multivibrators in time delay circuits and pulse generation. Examining the use of Astable Multivibrators as free-running oscillators in clock generation and tone generation. Clippers and Clampers Studying the working principles of Clippers, including positive and negative clippers. Understanding how Clippers are used in waveform shaping and noise elimination. Analyzing the operation and applications of Clampers in restoring AC-coupled signals to a specific voltage level. Differential Amplifier and CMRR Calculation Exploring the significance of Differential Amplifiers in communication and instrumentation applications. Calculating the Differential Gain and Common Mode Gain using h-parameters. Understanding the importance of Common Mode Rejection Ratio (CMRR) in noise rejection. Benefits: Provides in-depth explanations of critical topics related to Electronic Devices & Circuits. Equips students with the knowledge required to design and analyze electronic circuits. Covers essential concepts for digital circuit design and signal processing applications. Supports students in preparing for examinations and assignments related t

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Unit—3: Switching Characteristics of
Diodes and Transistors
1. Switching Characteristics of Diode and Transistor
1.1 Switching Characteristics of Diode and Transistor Turn ON/OFF Time
Switching characteristics are vital for understanding the behavior of electronic devices like
diodes and transistors when transitioning between different states. These characteristics are
particularly relevant in digital circuits and switching applications.
Diode Switching Characteristics:
● Turn ON Time: When a diode is initially in the OFF state (reverse-biased) and a forward
voltage is applied across it, it takes a certain time to overcome the depletion region’s
barrier and allow current flow. This time interval is known as the turn ON time of the
diode.
● Turn OFF Time: Conversely, when a diode is in the ON state (forward-biased) and the
voltage polarity across it is reversed, it takes a certain time for the diode to cease
conducting current. This duration is called the turn OFF time of the diode.
The switching times of diodes are essential in high-frequency rectifiers, switching power
supplies, and signal processing applications.
Transistor Switching Characteristics:
● Turn ON Time: In the context of transistors, the turn ON time refers to the time it takes
for the transistor to switch from its OFF state to the ON state. This process occurs when
the base-emitter junction is forward-biased sufficiently to allow current to flow between
the collector and the emitter.
● Turn OFF Time: The turn OFF time of a transistor is the time taken for the transistor to
switch from the ON state to the OFF state. This happens when the base-emitter junction
is reversed biased, halting the current flow through the collector-emitter path.

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Transistors are commonly used as switches in digital logic circuits, amplifiers, and power control
circuits.
1.2 Reverse Recovery Time of Diode
When a diode is conducting current in the forward-biased state, and the applied voltage across
the diode is suddenly reversed to make it reverse-biased, the diode does not instantaneously
stop conducting. Instead, it takes a short period to transition from the conducting state to the
non-conducting state. This time interval is known as the “Reverse Recovery Time” of the diode.
During this time, the excess charge carriers present in the diode’s semiconductor regions need
to recombine before the diode can completely block the current in the reverse direction. The
reverse recovery time is a critical parameter in power diodes used in high-frequency rectifiers
and switching circuits. It affects the diode’s switching efficiency and power loss during
high-speed switching.
1.3 Transistor as a Switch
Transistors, especially bipolar junction transistors (BJTs) and field-effect transistors (FETs), can
be utilized as electronic switches in various applications.
BJT as a Switch:
● When the BJT is in the ON state (active region), it acts as a closed switch, allowing
current to flow freely between the collector and emitter terminals.
● When the BJT is in the OFF state (cutoff region), it acts as an open switch, effectively
blocking any current flow between the collector and emitter terminals.
BJTs are commonly used as switches in digital circuits, amplifiers, and signal processing
applications.
FET as a Switch:
● In the ON state, the FET operates in its saturation region, allowing a significant current
flow between the source and drain terminals.
● In the OFF state, the FET operates in its cutoff region, effectively blocking any current
flow between the source and drain terminals.
FETs find applications in power control, low-power digital circuits, and switching applications.

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2. Multi-vibrators
2.1 Bistable Multivibrator
A bistable multivibrator, also known as a flip-flop, is a digital circuit capable of maintaining two
stable states indefinitely until an external trigger is applied to change its state. The bistable
multivibrator has two outputs, commonly denoted as Q and Q
̅ (complement of Q).
Operation: The bistable multivibrator can be constructed using various configurations, such as
cross-coupled transistors, NAND gates, or NOR gates. When one output (e.g., Q) is HIGH (logic
1), the other output (e.g., Q
̅ ) will be LOW (logic 0), and vice versa. Once set in one of the stable
states, it remains in that state until an external trigger is received, causing it to switch to the
other stable state.
Applications: Bistable multivibrators are widely used in digital circuits for memory elements,
such as D flip-flops, T flip-flops, JK flip-flops, and SR flip-flops. They also form the fundamental
building blocks of counters, registers, and state machines in digital systems.
2.2 Monostable Multivibrator
A monostable multivibrator, also known as a one-shot multivibrator, has only one stable state
and requires an external trigger to switch to the unstable state momentarily. After a predefined
time duration, it returns to its stable state automatically.
Operation: The monostable multivibrator circuit includes one energy storage element, typically
a capacitor. When triggered, the capacitor charges or discharges to change the state of the
circuit. The output remains in the unstable state for a fixed duration determined by the values of
external resistors and capacitors connected to it.
Applications: Monostable multivibrators are used in applications requiring a precise time delay
or pulse generation. They are used in timers, pulse generators, debouncing circuits, and
time-delay relays.
2.3 Astable Multivibrators
Astable multivibrators are free-running oscillators that continuously switch between two unstable
states without any external triggering.

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Operation: Astable multivibrators do not have any stable state, unlike bistable and monostable
multivibrators. The circuit continuously alternates between its two unstable states, generating a
continuous square wave or pulse train at its output.
Applications: Astable multivibrators are widely used in applications like clock generation,
frequency division, tone generation, and pulse-width modulation (PWM) for motor control and
power electronics.
3. Clippers and Clampers
3.1 Clippers
Clippers, also known as limiters, are electronic circuits used to clip or remove a portion of an
input signal that exceeds a specified voltage level. Positive and negative clippers can be
employed to shape the waveform according to the desired output.
Positive Clippers: A positive clipper removes the positive portion of the input signal that
exceeds a predetermined voltage level. The output waveform will only show the negative part of
the input signal below the clipping voltage.
Negative Clippers: A negative clipper removes the negative portion of the input signal that falls
below a specified voltage level. The output waveform will only display the positive part of the
input signal above the clipping voltage.
Applications: Clippers are widely used in audio and video signal processing, waveform
shaping, and noise elimination in communication systems.
3.2 Clampers
Clampers, also known as DC restorers or level shifters, are circuits used to add or “clamp” a DC
level to an AC waveform. The purpose of clampers is to set a reference voltage level for the AC
signal. This is particularly useful when the AC signal is to be further processed, and any DC
offset needs to be removed.
Positive Clampers: A positive clamper adds a positive DC level to the input signal. It shifts the
entire waveform upwards, ensuring that the most negative point of the waveform aligns with the
reference DC level.

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Negative Clampers: A negative clamper adds a negative DC level to the input signal. It shifts
the entire waveform downwards, aligning the most positive point of the waveform with the
reference DC level.
Applications: Clampers are commonly used in display systems, where AC-coupled signals
need to be restored to a specific voltage level for proper visualization. They are also used in
communication systems and signal processing applications.
4. Differential Amplifier and CMRR Calculation
4.1 Differential Amplifier
A differential amplifier is a type of electronic amplifier that amplifies the difference between two
input signals while rejecting any signals that are common to both inputs (common-mode
signals). Differential amplifiers are critical components in various electronic systems, especially
in communication and instrumentation applications.
Operation: A differential amplifier usually consists of two transistors, often implemented with
BJTs or FETs, and resistors connected in a differential configuration. The input signals are
applied to the bases (for BJTs) or gates (for FETs) of the transistors, and the amplified output is
taken from the collectors (for BJTs) or drains (for FETs). The differential amplifier amplifies the
voltage difference between the two input signals while attenuating any signal that is common to
both inputs.
Applications: Differential amplifiers are extensively used in balanced communication systems,
audio signal processing, instrumentation amplifiers for precise measurements, and in various
sensor interfaces.
4.2 Calculation of Differential Gain, Common Mode Gain, and CMRR using h-parameters
In differential amplifier analysis, h-parameters (also known as hybrid parameters or two-port
parameters) are commonly used to relate the input and output voltages and currents of the
amplifier.
Differential Gain: The differential gain, often denoted by Ad, is the ratio of the change in the
output voltage to the change in the differential input voltage. It quantifies how effectively the
amplifier amplifies the difference between the two input signals.
Common Mode Gain: The common-mode gain, often denoted by Ac, is the ratio of the change
in the output voltage to the change in the common-mode input voltage. It indicates how much

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the amplifier amplifies any input signal that appears simultaneously and identically at both
inputs.
Common Mode Rejection Ratio (CMRR): The CMRR is a crucial parameter that quantifies the
differential amplifier’s ability to reject common-mode signals. It is calculated by dividing the
differential gain (Ad) by the common-mode gain (Ac). CMRR is typically expressed in decibels
(dB).
Importance: CMRR is particularly crucial in applications where the differential amplifier needs to
amplify small differential signals while rejecting common-mode noise effectively. High CMRR
ensures accurate and noise-free measurements in various sensor and communication systems.
By mastering these topics, students will gain a comprehensive understanding of electronic
devices, their behavior, and practical applications in modern engineering. These fundamental
concepts form the backbone of electronic circuit design and analysis and are essential for any
aspiring computer science engineer.