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ASSIGNMENT
TECHNOLOGY PARK MALAYSIA
AENG001-3.5-2-AEANALOGUE ELECTRONICS
UCD2F1409E&E
HAND OUT DATE: 29th MAY 2015WEIGHTAGE: 50
NAME : JOSHUA JEBARAJ A/L JOSEPH
TP NUMBER: TP032057
LECTURER : MR. SARDAR ALI
Contents
Introduction...........................................................................................................................................2
Design for a Common Emitter circuit.....................................................................................................3
Design of a voltage divider bias.............................................................................................................8
Hardware Implementations.................................................................................................................11
Results.................................................................................................................................................13
Discussion............................................................................................................................................15
Conclusion...........................................................................................................................................16
References...........................................................................................................................................17
Introduction
This assignment is based on Common Emitter Amplifier with current divider bias. For
this assignment , I was required to demonstrate the understanding of the theoretical and
intuitive behavior a simple analogue circuit. I was also asked to apply the knowledge I
learned and solve the problems of the Common Emitter and the Common Source Amplifiers.
During this experiments , the NI MULTISIM software was used as a tool to create a
prototype before building the circuit.
The Common Emitter amplifier consists of transistors. Transistors can be divided into
two categories , one of the transistors named NPN and the other PNP. This experiment is
based on using NPN transistors. Transistors are basically controlling the amplification of a
allows a small current or voltage to control the flow of a much larger current from a dc power
source. The transistor has three pins , one is called emitter , the second is called base and the
third is called collector.
By using this transistor , we can design a Common Emitter amplifier and calculate the
value of the base , collector and emitter current as well as the values of the resistors that are
needed for building the circuit with the help of the data sheet and the properties of the
transistors. After creating the circuit , this assignment also included the voltage divider bias
by using the coupling capacitors. The coupling capacitors are used in many types of circuits
where AC signals are the desired signals to be output while DC signals are just used for
providing power to certain components in the circuit but should not appear in the output. By
carrying out this experiment , the importance of the coupling capacitors are noticed and how
it affects the end results.
Design for a Common Emitter circuit.
Calculation
Figure 1 : General diagram of a CE circuit
The values of Beta and VBE is taken from the properties of the transistor
Diagram 1 : The beta value of the 2N2219 transistor
Diagram 2 : The VBE of the 2N2219 transistor.
Given data from the datasheet for 2N2219 Transistor
β = 172.023
VA = 13.1259V
VBE = 0.8319V
Ic = 1mA
F = 1kHz
DC analysis
Vcc – IBRB – IERE – VBE = 0…………………………… (1)
Vcc – ICRC – ICRC – VCE = 0…………………………… (2)
Ic = ΒIB = IEIB ………………...…………………………. (3)
IB = I_C/β = IE – IC………………………….…………… (4)
IE = Ic + IB………………………………………………… (5)
Vcc – IBRB – VBE – IERE = Vcc – ICRC – VCE – IERE ……………….. (6)
From (6)
– IBRB – VBE = – ICRC – VCE
VCE – IBRB + ICRC – VBE = 0
(V_BE+I_BR_B–V_CE)/"IC"=RC……………………………………… (7)
(7) Substitute into (2)
Vcc – ICRC – ICRC – VCE = 0
(Vcc – ICRC – VCE ) / IC = RC
(Vcc – ICRC – VCE ) / I_C = (VBE + IBRB – VCE ) / "IC"
………………………………………………………..… (8)
Since,
IB = I_C/β = 5.81 x 10-6 A
IE = IC + IB = 1.006 x 10-3 A
Hence,
(VCC - ICRC – VCE – IERE=0 ),
To find RC ,
12- 1m(RC)- 10 – IERE = 0 ,
2- 1m(RE)- 1mRE=0 ,
2 – 1m(RE) = 1mRC ,
RC = 2 – 1mRE / 1m
RC = 2k - RE
AC Analysis
Figure 2 : Hybrid pi model
The figure above shows the hybrid pi model of the circuit.
Gain = V_0/V_s = -gm (r0 || Rc)
gm = I_c/V_T = (1 x 〖10〗^(-3))/〖26 x 10〗^(-3)
gm = 38 x 10-3
r0 = V_A/I_c = 13.1259/(1 x 〖10〗^(-3) )
= 13.126 k
Therefore,
Av = -gm (r0 || RC)
50 = -0.038 ((13.125k x RC) / (13.125k + RC ))
1.32 x 103 = (13.125k x RC) / (13.125k + RC )
1.32 x 103 (13.125 + RC) = 13.125k x Rc
17.325 x 103 = 11.805 x 103 . Rc
Rc = 17.325M /11.805
Rc = 1442.99
To find RE,
RC = 2k – RE
1442.99 = 2k – RE
RE = 2k – 144.99
RE = 557
Design of a voltage divider bias.
The voltage divider bias is designed using a software named NI MULTISIM. NI
MULTISIM is used in various electronic circuit designing.
The choice of the transistor was 2N2219. After selecting and calculating the values of
RC , RB and RE , the values of the resistors were selected in the NI MULTISIM software.
The circuit was built with the theoretical values that were calculated earlier.
Figure 3 : Set up of the MULTISIM simulator
By using these values , the comparison between the calculation of the Amplitude
frequency was done In the theoretical aspects , the calculated Amplitude Gain was 50V. In
the simulation run , the amplitude gain was 46V. After connecting to the oscilloscope our
results was as below.
By analyzing the V(rms) from the probe 1 and probe 5 , the gain was calculated.
The calculated gain was 40V. It is almost the theoretical value that was calculated which is
50V.
Figure 4 : The simulation oscilloscope results
The oscilloscope showed the input current was amplified once it reached the output of
the circuit. This proved that the work of the coupling capacitors were working. A coupling
capacitor is a capacitor used to separate the various stages in a circuit, for example, to
separate the stages of a multi staged amplifier. It separates the dc and ac components and
'couples' the output of one stage to the input of the next stage. The basic function of coupling
capacitors is to remove noise or other disturbances and make sure the output of previous
stage is compatible with one that were inputted. In other words , the coupling capacitor made
sure that there was a link from one stage of the circuit to the other stage of the circuit by
blocking the DC source which only needed for the power.
Moreover , while running the simulation process , it also noticed that there were only
slight differences from. the theoretical aspects.
Hardware Implementations.
Once the simulation was done , the experiment was conducted using hardware.
We connected the circuit as the one done in the simulation.
Figure 5 : The set up of apparatus used for the Lab testing
Once the circuit was connected without the capacitors , the value of IB and IC was
calculated and checked with the theoretical values. The results was different in few decimal
places.
After the calculation of the Common emitter was done , the voltage biasing was done by
inserting the capacitors following the simulation. The value of the gain was compared with
the simulation. The results of the oscilloscope also was compared. And it was almost the
same with slight differences.
Figure 6 : Results of the Lab oscilloscope
It is noticed here that there is distortion of a little noise although the coupling
capacitors were used. The noise appears might be from the temperature aspects. The end of
the experiment showed that , the signal was amplified from the input , and the coupling
capacitor allowed the AC to pass by having a low impedance. The coupling capacitor did not
let the flow of DC to pass as it has high impedance when a higher frequency signal hits it.
This makes the coupling capacitor useful as the DC power supply was only needed for power
and it might damage the circuit if it was let pass.
Bypass capacitor , A capacitor that filters out the AC signal removing the noise and
provides a DC signal is known as a bypass capacitor. The capacitor connected in the figure
below is a bypass capacitor bypassing AC noise and allowing pure DC signal to pass through
the component.
Results
The gain calculated in the theoretical value is 50 V. Once the prototype was run , the
gain that was observed was 41 V.
Figure 7 : The prototype oscilloscope
Once the lab was done , the gain was observed as 30V.
Figure 9 :
Practical Oscilloscope
This difference is observed due to many factors influencing. The noise was one of the
factors. Thermal noise was the unavoidable noise. This may be the generated thermal motion
of charge carriers usually caused by the electron inside the component. Besides that , the
loose connections in the circuit component causing a very wide range in frequencies. In
addition , the efficiency of the capacitors that were bought were also not that efficient as it
might have allowed a small quantity of DC to pass.
Also the efficiency of the bypass capacitors was also put to test because of the
presence of the noise in the circuit. The inefficiency of bypass capacitor causes noise
distortion , which influenced the changed the results comparison with the theoretical and
simulation results.
Discussion
The Common Emitter Circuit has many analysis and differs from the theoretical ,
simulation and the practical implementation. This is because in the theoretical aspects , the
value of IB , RB , IC , RC , IE and RE were calculated and found out by referring the data
sheet. When the values were transferred into the simulation process , the value of RB , RC
and RE were not found as only specific resistors values were only provided. That is why the
results were slightly different. When it was carried out in the lab , certain resistors were not
found in the market and we chose resistors that had value near to the calculated resistor.
Therefore , the result in the simulation was different than of the practical. Besides that , even
with difference in resistors , the final product was same although slight difference from the
value originally calculated.
There’s also the difference in the gain. This is due to when we calculated theoretically
, the gain was assumed at first to get the values of RB , RC and RE. When we simulated the
circuit , all the calculated values were put in. When the simulation was done , it is noticed
that the gain was only. This is because the values of the coupling capacitors were not
calculated and the fact that the noise were also not taken into consideration as well. This
makes a slight difference in having the theoretical values calculated and the practical values.
This difference is observed due to many factors influencing. The noise was one of the
factors. Thermal noise was the unavoidable noise. This may be the generated thermal motion
of charge carriers usually caused by the electron inside the component. Besides that , the
loose connections in the circuit component causing a very wide range in frequencies. In
addition , the efficiency of the capacitors that were bought were also not that efficient as it
might have allowed a small quantity of DC to pass.
Conclusion
As a summary , the Common emitter circuit is used to amplify the signal from the
input to the output. The coupling capacitors looks small but it was an important component of
the circuit. The coupling capacitor is used to make sure the DC does not pass by having high
impedance on high frequency because DC was only needed for power. It only let AC pass ,
by having a low impedance on low frequencies as AC helps the amplification process and the
capacitors helps to connect this coupled circuit. The difference in gain was also an issue but
there were not much difference as the assumed value was 50V and the gained value was 46V.
This was due to noise factors such as temperature. The calculation of RB , RC and RE was
also important as without those values , this experiment was nothing. The difference of data
in which is achieved can be analyzed in many ways. Some of the ways were done in this
experiment because there were some errors at the beginning , but we managed to overcome it
by troubleshooting.
References
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What do coupling capacitors really do in AC amplifiers? Are they rechargable "batteries"
conveying voltage variations or diverting biasing currents?. 2015. What do coupling
capacitors really do in AC amplifiers? Are they rechargable "batteries" conveying voltage
variations or diverting biasing currents?. [ONLINE] Available at:
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http://electronics.stackexchange.com/questions/60694/role-of-capacitors-in-amplifier.
[Accessed 23 May 2015].
Bypass Capacitors – Why and How to Use Them? » Electro-Labs.com. 2015. Bypass
Capacitors – Why and How to Use Them? » Electro-Labs.com. [ONLINE] Available at:
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May 2015].