Exp.
No : 5 Reg No:20BEC1119
Date : 20-9-2021
CASCODE AMPLIFIER
AIM:
To construct the cascode amplifier circuit by using LTspice
software and verify its transient response curve and frequency response
curve and to calculate the bandwidth of the amplifier.
APPARATUS REQUIRED:
LTSPICE Software
Personal Computer
Si.No Name of the Specification/Range Quantity
Component /
Equipment
1 BJT transistor Model-2N2222 2
2 Voltage source (DC 10v 1
SUPPLY)
3 AC supply 1k frequency 1
4 Resistors - 6
5 Capacitors - 4
6 Ground - 1
THEORY:
Working principle: The cascode is a two-stage amplifier that consists of a
common-emitter stage feeding into a common-base stage. The load in the amplifier
stacked vertically and it is referred to as cascode connection. The first stage
configuration is connected in parallel to the second stage configuration of the
transistor. To isolate and avoid direct feedback from the output to the input. This
type of connection is known as cascode.
In modern circuits, the cascode is often constructed from two transistors (BJTs or
FETs), with one operating as a common emitter or common source and the other as
a common base or common gate.
The cascode improves input–output isolation (reduces reverse transmission), as
there is no direct coupling from the output to input. This eliminates the Miller effect
and thus contributes to a much higher bandwidth.
The characteristics due to the cascoding of amplifiers are:
• The impedances at input and output are high.
• The signals amplification undergoes under high bandwidths possessed by
the system.
• The isolation amid input and the output is high.
As there is no direct communication or coupling from output to input because of high
isolation leads to eliminate the miller effect.
Advantages:
The advantages of the cascode amplifier are:
• The bandwidth is high due to the elimination of the Miller Effect.
• Due to the cascode connection between two transistors the overall gain of
the system is high.
• Even the parts of the count for both the transistors are low.
• Cascode circuit offers increased gain, stability, enhanced impedance levels,
more bandwidth levels, and slew rate.
• The construction of the circuit is so simple.
• Cascode amplifier is implemented as a multiplying mixer in the
superheterodyne receivers.
Disadvantage:
The disadvantages of these amplifiers are:
• The presence of two transistors requires a high amount of voltage supply.
• The sufficient amount of drain to source voltage must be supplied to both the
transistor which strikes lesser the limit on the supply voltage.
Applications :
The applications of these amplifiers are:
• In the RF tuners, cascode amplifiers are used.
• Amplitude modulation technique uses cascoding technique.
DESIGN:
PROCEDURE:
1. Open LTspice.
2. Click on the New schematic.
3. Connect the circuit as per the circuit diagram given in Experiment from the
parts of library and save the schematic.
4. Assign values to all the components connected in the circuit daigram.
5. Give the ground connection.
6. Click on Simulate. Go to edit simulation cmd. Simulation settings window will be
displayed.
7. Select the operating analysis first and then select transient analysis to get
the graph .
8. Then select ac analysis to get frequency response.
9. Run the simulation.
10. Obtain the graph corresponding to the experiment.
CALCULATIONS:
LTSPICE CIRCUIT DIAGRAM:
LTSPICE OUTPUT:
Fig no 1: operating point analysis of cascode Amplifier
Fig no 2: Transient Response Curve of cascode Amplifier ( Input waveform)
Fig no 3: Transient Response Curve of cascode Amplifier (Output Waveform)
Fig no 4: Frequency Response Curve of cascode Amplifier (AC analysis)
RESULT : Cascode amplifier circuit was constructed and the transient
response and Frequency response curve are verified.
Bandwidth = Higher Cutoff frequency (F2) - Lower cutoff frequency (F1)
=35285.184-20.95987 Hz
= 35.285163 MHz
