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AB-17
COMMON BASE
AMPLIFIER
ANALOG LAB
EXPERIMENT BOARD
Ver. 1.0
An ISO 9001: 2000 company
94-101, Electronic Complex, Pardesipura INDORE-452010, India.
AB-17
Tel.: 91-731-2570301 Fax: 91-731-2555643
Email: [email protected] Web: www.scientech.bz
Scientech Technologies Pvt. Ltd.
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AB-17
COMMON BASE AMPLIFIER
AB-17
TABLE OF CONTENTS
1.Introduction
3
2. Theory
5
3.Experiment
11
To study the Common Base Amplifier (NPN)
and to evaluate –
Operating Point of the Common Base Amplifier
Voltage gain, Current gain of the Amplifier AV, Ai
Input and Output impedance of Amplifier.
4.Datasheet
13
5.Warranty
15
6.List of Service Centers
16
7.List of Accessories with AB-17
16
Scientech Technologies Pvt. Ltd.
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AB-17
INTRODUCTION
AB-17 is a compact, ready to use COMMON BASE AMPLIFIER
experiment board. This is useful for students to understand the functionality
of common base amplifier and to study various operational parameters of an
transistor Amplifier. It can be used as stand alone unit with external DC
power supply or can be used with SCIENTECH ANALOG LAB ST-2612
which has built in DC power supply, AC power supply, function generator,
modulation generator, continuity tester, toggle switches, potentiometer.
List of Boards :
Model
AB-01
AB-02
AB-03
AB-04
AB-05
AB-06
AB-07
AB-08
AB-09
AB-15
AB-16
AB-18
AB-19
AB-21
AB-22
AB-23
AB-26
AB-28
AB-29
AB-30
AB-31
AB-32
AB-33
AB-41
AB-42
AB-43
Name
Diode characteristics (Si, Zener, LED)
Transistor characteristics (CB NPN)
Transistor characteristics (CB PNP)
Transistor characteristics (CE NPN)
Transistor characteristics (CE PNP)
Transistor characteristics (CC NPN)
Transistor characteristics (CC PNP)
FET characteristics
Rectifier Circuits
Common Emitter Amplifier
Common Collector Amplifier
RC-Coupled Amplifier
Cascode Amplifier
Class A Amplifier
Class B Amplifier (push pull emitter follower)
Class C Tuned Amplifier
Phase Locked Loop (FM Demodulator &
Frequency Divider/Multiplier)
Multivibrators (Astable / Monostable)
F-V and V-F Converter
V-I and I-V Converter
Zener Voltage Regulator
Transistor Series Voltage Regulator
Transistor Shunt Voltage Regulator
Differential Amplifier (Transistorized)
Operational Amplifier (Inverting / Noninverting / Differentiator)
Operational Amplifier (Adder/Scalar)
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AB-17
AB-44
AB-45
AB-51
AB-52
AB-53
AB-56
AB-65
AB-66
AB-67
AB-81
AB-82
AB-83
AB-84
AB-90
AB-91
AB-92
AB-93
Operational Amplifier (Integrator/
Differentiator)
Schmitt Trigger and Comparator
Active filters (Low Pass and High Pass)
Active Band Pass Filter
Notch Filter
Fiber Optic Analog Link
Phase Shift Oscillator
Wien Bridge Oscillators
Colpitt Oscillator
Kirchoff’s Laws (Kirchoff’s Current Law &
Kirchoff’s Voltage Law)
Thevenin’s and Maximum power Transfer
Theorem
Reciprocity and Superposition Theorem
Tellegen’s Theorem
Two port network parameter
Optical Transducer (Photovoltaic cell)
Optical Transducer (Photoconductive cell/LDR)
Optical Transducer (PhotoTransistor)
…and many more
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AB-17
THEORY
Amplification is the process of increasing the strength of signal. An
Amplifier is a device that provides amplification (the increase in current,
voltage or power of signal) without appreciably altering the original signal.
Bipolar transistors are frequently used as an amplifiers. Transistor can be
used as an Amplifier in three configurations:
1.
Common Base
2.
Common Emitter
3.
Common Collector
Common Base Configuration :
In this arrangement, the input signal is applied between emitter and base
and the output is taken from the collector to base shown in Fig 1. In this
arrangement input current is emitter current and output current is collector
current.
Current relations in CB configurations
IE = IC + IB
IC = α / (1- α ) IE + 1 / (1-α ) ICBO
α = IC / IE
Where IC = Collector current
IE = Emitter current
ICBO = current through collector to base when emitter is open.
α = Common Base DC current gain. α ranges between .9 - .99.
Fig. 1
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Transistor as an Amplifier in CB configuration :
The conditions for which transistor works as an amplifier are:
1.
Emitter base junction is always forward biased.
2.
Collector - Base junction is always reverse biased.
To achieve this, a DC voltage VEE is applied in the input circuit in addition
to signal shown in Fig 1. this voltage is known as bias voltage and it's
magnitude is such that it always keep the input circuit forward biased
regardless the polarity of signal.
A input circuit has low resistance, therefore a small change in signal voltage
causes a appreciable change in emitter current, this causes almost same
change in collector current due to transistor action. The collector current is
flowing through high load resistance Rc produces a large voltage across it,
thus a weak signal applied in the input circuit appears in the amplified form
in collector circuit.
Operation of Common Base Amplifier :
In order to get faithful amplification, the transistor is properly DC biased.
The purpose of DC biasing is to obtain a certain DC collector current(Ic) at
a certain DC collector voltage(VCB). These values of current and voltage are
called operating point (Quiescent point). To obtain DC operating point
some biasing methods are used called biasing circuits. These biasing
arrangements should be such as to operate the transistor in Active region.
The Most commonly used Biasing circuits is voltage divider method. In this
method two resistances R1. and R2 are connected across the supply voltage
VCC and provide proper biasing. A voltage divider formed by R1 and R2. The
voltage drop across R2 forward biased the base emitter junction which
causes the base current to flow. Thus, collector current flows even in zero
signal condition. Resistance RE provides stabilization.
V2 = VCC * R2 / (R1 + R2)
V2 = VBE + VE
V2 = VBE + IERE
IE = (V2 - VBE) / RE
IE is approx. equal to IC.
IC = (V2 - VBE) / RE
VCE = VCC - IC (RC + RE)
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AB-17
Fig. 2
This method is widely used because operating point of transistor can be
made almost independent of beta (β) and provides good stabilization of
operating point.
If this circuit is used to amplify AC voltages, some more components must
be added to it.
Coupling Capacitors (CC): They are used to pass AC input signal and block
the DC voltage from the preceding circuit. This prevents DC in the
circuitory on the left of coupling capacitor from affecting the bias on
transistor. The coupling capacitor also blocks the bias of transistor from
reaching the input signal source. It is also called blocking capacitor.
Bypass Capacitors(CE): It bypasses all the AC current from the emitter to
the ground. If the capacitor CE is not put in the circuit, the AC voltage
developed across RE will affect the input AC voltage, such a feedback is
reduced by putting the capacitor CE.
Rc: It represents the load resistance is connected at the output.
In this amplifier input signal is injected in to base-emitter circuit and output
signal is taken out from the base-collector circuit.
When positive Half cycle of the signal is applied then,
1.
Forward biased is decreased, since Vbe is negative w.r.t. collector ie.
ground.
2.
Base current is decreased.
3.
Emitter current is decreased, similarly collector current is also
decreased
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AB-17
4.
Drop across IcRc is decreased,
5.
Hence Vcb is increased, consequently positive half-cycle of the
output is obtained. i.e. input and output are in phase with each other.
Fig. 3
Fig 3 Input and Output Waveforms of Common Base Amplifier with load
resistance 1KΩ
Operating Parameter of Common Base Amplifier
Voltage Gain :
It is the ratio of output voltage (Vout) obtained to input voltage (Vin).
AV = VOut / Vin
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AB-17
Fig 4
Input Impedance :
It is the ratio of Input votage (Vin) to Input Current (Ii).
Zin = Vin / Ii
To measure the input impedance a known resistor (Rs) is placed in series
before the input coupling capacitor and the impedance could be calculated
using the equation.
Zin = Rs / (Av/Av`-l)
Where
Av = voltage gain without the resistor (Rs)
Av`= voltage gain with the resistor (Rs)
Output Impedance :
It is the ratio of Output voltage (Vout) to Output Current (Io).
Zout = Vout /Io
To measure the Output impedance a known resistor (Rs) is placed from
output to ground and the output impedance could be calculated using the
equation
Zout = (Av / Av`-l) * Rs
Where
Av = voltage gain without the resistor (Rs)
Av’ = voltage gain with the resistor (Rs)
Current gain : It is the ratio of Output current (Io) to Input current (Ii).
Ai = Io / Ii
The Current gain could be calculated using the equation
Ai = - Av * Zin / RL
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Characteristics of Common Base Amplifier :
1.
It produces no phase reversal of input signal i.e., input and output
signals are in phase with each other.
2.
It has high voltage gain.
3.
It has moderately low input impedance.
4.
It has large output impedance.
5.
It has current gain (β) less than one.
Comparisons of Amplifiers Configurations :
Type of Amplifier Circuit
Characteristic
Common
Base
Common
Emitter
Common
Collector
Phase reversal
No
Yes
No
Voltage Gain
High
Highest
Nearly Unity
Input
Impedance
Lowest
Moderate
Highest
Ouput
Impedance
Highest
Moderate
Lowest
Current Gain
Nearly unity
High (β)
Highest (β + 1 )
Scientech Technologies Pvt. Ltd.
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AB-17
EXPERIMENT
Object :
To study the Common Base Amplifier and to evaluate –
Operating Point, Voltage gain (AV), Input impedance, and output
impedance Current gain (Ai) of amplifier.
Apparatus Required :
1.
Analog board of AB-17.
2.
DC power supplies +12V external source or ST -2612 Analog Lab.
3.
Digital Multimeter
4.
2 mm patch cords.
Circuit Diagram :
Circuit used to study Common Base Amplifier is shown in Fig 5.
Fig. 5
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AB-17
Procedure :
1.
Connect Testpoint 2 and Testpoint 3, Testpoint 4 and Testpoint 5,
Testpoint 6 and Testpoint 7, using 2mm patch cords.
2.
Connect +12V DC power supply at their indicated position from
external source or ST -2612 Analog Lab.
3.
Switch ON the power supply.
4.
For the measurement of Quiescent Point measure the VCB by
connecting Voltmeter between Testpoint 4 and Testpoint 6 Measure
Collector current (Ic) by connecting Ammeter between Testpoint 4
and Testpoint 7.
5.
Connect a sinusoidal signal of 10mV(p-p) at 25KHz frequency at the
Testpoint 1 (Input of amplifier) from external source or ST-2612
Analog Lab.
6.
Observe the amplified output on oscilloscope by connecting
Testpoint 8 (output of amplifier) to oscilloscope.
7.
Calculate Voltage gain of amplifier. Connect Load resistor of 1K
ohms at the output and find the voltage gain of amplifier with load
resistor.
8.
Calculate input impedance, output impedance, and current gain of
amplifier using the mentioned formulas with resistance 1K.
Result :
Operating Point of the Common Base amplifier
IC = ______________mA
VCB =______________V
Voltage gain of the amplifier AV
=________________
Input impedance of amplifier Zin
=________________
Output Impedance of amplifier Zout =________________
Current gain of amplifier Ai
Scientech Technologies Pvt. Ltd.
=________________
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AB-17
DATASHEET
Scientech Technologies Pvt. Ltd.
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AB-17
Scientech Technologies Pvt. Ltd.
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AB-17
WARRANTY
1) We guarantee the instrument against all manufacturing defects during
24 months from the date of sale by us or through our dealers.
2) The guarantee covers manufacturing defects in respect of indigenous
components and material limited to the warranty extended to us by the
original manufacturer, and defect will be rectified as far as lies within
our control.
3) The guarantee will become INVALID.
a) If the instrument is not operated as per instruction given in the
instruction manual.
b) If the agreed payment terms and other conditions of sale are not
followed.
c) If the customer resells the instrument to another party.
d) Provided no attempt have been made to service and modify the
instrument.
4) The non-working of the instrument is to be communicated to us
immediately giving full details of the complaints and defects noticed
specifically mentioning the type and sr. no. of the instrument, date of
purchase etc.
5)
The repair work will be carried out, provided the instrument is
dispatched securely packed and insured with the railways. To and fro
charges will be to the account of the customer.
DESPATCH PROCEDURE FOR SERVICE
Should it become necessary to send back the instrument to factory please
observe the following procedure:
1) Before dispatching the instrument please write to us giving fully details
of the fault noticed.
2) After receipt of your letter our repairs dept. will advise you whether it
is necessary to send the instrument back to us for repairs or the
adjustment is possible in your premises.
Dispatch the instrument (only on the receipt of our advice) securely packed
in original packing duly insured and freight paid along with accessories and
a copy of the details noticed to us at our factory address.
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AB-17
LIST OF SERVICE CENTERS
1. Scientech Technologies P. Ltd.
90, Electronic Complex
Ph: (0731) 5202959
Pardesipura,
Email: [email protected]
INDORE – 452010
2. Scientech Technologies P. Ltd.
First Floor,
Ph.: (011) 26513912, 26864943
14, Uday Park,
Fax: (011) 26864943.
NEW DELHI – 110049
Email: [email protected]
3. Scientech Technologies P. Ltd.
New no.2, Old no.10, 4th street Ph.: (044) 52187548, 52187549
Venkateswara nagar, Adyar
Fax: (044) 52187549
CHENNAI – 600025
Email: [email protected]
4. Scientech Technologies P. Ltd.
202/19, 4th main street
Ph.: (080) 51285011
Ganganagar,
Fax: (080) 51285022
BANGALORE- 560032
Email: [email protected]
5. Scientech Technologies P. Ltd.
First floor, L block
Ph.: (022) 56299547
Ranjit studio compound,
Fax: (022) 24155984
Dada Saheb Phalke road,
Email: [email protected]
Dadar (East)
MUMBAI – 400014
6. Scientech Technologies P. Ltd.
988, Sadashiv Peth,
Ph.: (020) 24461673
Gyan Prabodhini Lane,
Fax: (020) 24482403
PUNE – 411030
Email: [email protected]
LIST OF ACCESSORIES
1.
2mm Patch cord (red) .........................................................1 Nos.
2.
2mm Patch cord (black) ......................................................3 Nos.
3.
2mm Patch cord (blue) ........................................................5 Nos.
Scientech Technologies Pvt. Ltd.
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