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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Bypass Capacitors – Why and How to Use Them? » Electro-Labs.com. 2015. Bypass

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