Differential Amp Report

7/29/2019 Differential Amp Report

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Report

Project 1

Design and analysis of a Direct-Coupled

Transistor Amplifier

30 Nov 2011

By

Alexis Chrysaphis


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Table of ContentsObjectives ...................................................................................................................................................................... 3

Introduction ................................................................................................................................................................... 3

Pre-Lab ...................................................................................................................................................................... 6

Equipment List ........................................................................................................................................................... 6

Components List ........................................................................................................................................................ 7

Equations ................................................................................................................................................................... 7

Lab Work ........................................................................................................................................................................ 8

Day 1.......................................................................................................................................................................... 8

Section A Breadboard ......................................................................................................................................... 8

Section B How components get connected to breadboard ............................................................................... 8

Section C Power Supplies ................................................................................................................................... 9

Section D What to Know Before Powering On ................................................................................................... 9

Results Day 1 ...................................................................................................................................................... 9

Day 2........................................................................................................................................................................ 10Section AICs socket ........................................................................................................................................ 10

Section B Procedure ......................................................................................................................................... 10

Section C Table of Measurements ................................................................................................................... 11

DC and AC analysis of the circuit......................................................................................................................... 11

Results Day 2 .................................................................................................................................................... 11

Day 3 ..................................................................................................................................................................... 12

Section A Zener Diode ....................................................................................................................................... 12

Section B Procedure .......................................................................................................................................... 12



Results Day 3 .................................................................................................................................................... 13

Day 4 ..................................................................................................................................................................... 14

Section A Level Shifting ..................................................................................................................................... 14


Section CMeasurements .................................................................................................................................. 15


Results Day 4 .................................................................................................................................................... 15

Day 5 ..................................................................................................................................................................... 16

Section A Final Stage ......................................................................................................................................... 16




Results Day 5 .................................................................................................................................................... 17

Final Result Presentation to Client ........................................................................................................................... 18


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ObjectivesThe aim of the project is to design and build a differential, direct-coupled amplifier having a high

differential gain and low common-mode gain. It has this name because this circuit amplifies the

difference between two input voltages. A two-transistor configuration is the heart of the amplifier and

an ideal form of the circuit will be showed and analyzed in the following report. In most real-world lab,

the use of operational amplifiers or some sort of differential amplification scheme is in constant use. Acircuit analysis program Multisim will be used as a design tool to check the feasibility of each circuit

stage and simulate the behavior of the overall design.

IntroductionThe design of the amplifier was done as series of circuit stages. First the differential input stage (fig.1)

will take the place, which is the heart of the amplifier.

Figure 1: Differential Input Stage

As mentioned above, it is called differential because the final output voltage will be the difference of the

two. A differential amplifier can be done in 4 different setups. First is the differential input, differential

output (fig.2) which has 2 inputs and 2 outputs.

Figure 2: Differential input and output


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Then, is the single ended input, differential output (fig.3) which has 1 input but again 2 outputs.

Figure 3: Single Ended Input Differential Output

After these two, the differential input, single ended output (fig.4) exists that has 2 inputs and 1 output.

Figure 4: Differential Input Single Output

Finally, is the single ended input single ended output (fig.5), having 1 input and 1 output.

Figure 5: Single Ended Input and Output

In this experiment, the former was the best choice of use because the differential amplifier having two

outputs will raise a problem if a connection to another circuit that follows wants to be done.


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The following table will summarize the characteristics of each amplifier.

Table 1: Differential Amplifier Setups

Input Output Vin Vout

Setup 1 Differential Differential v1-v2 Av(Vc2-Vc1)

Setup 2 Single-ended Differential V1 or v2 Av(Vc2-Vc1)

Setup 3 Differential Single-ended V1-v2 Av(Vc2)

Setup 4 Single-ended Single-ended V1 or v2 Av(Vc2)

Following the design, the second stage is to build a current source to improve the Common Rejection

Ration (CMRR). This was done by replacing the emitter resistor by a current source (fig.6). By choosing

the correct Zener diode voltage and the values of the resistors, a suitable current in the emitter circuit of

the differential pair was achieved. All necessary changes in the collector load resistors were done in

order to maintain a suitable operating point for the transistor. Measurements were taken.

Figure 6: Current Source using Zener Diode

The next stage was the design of a level shifting stage (fig.7). An ideal differential amplifier has zero

output voltage for zero input voltage. In our case, when both signals were zero, the output of the

differential stage was at some positive potential. To erase this minor fault and achieve the ideal

differential amplifier the level-shifting stage was done. This was done using the existing voltage

reference in the emitter circuit of the differential input pair and also with the selection of appropriate

values of components that gave an output signal of zero when both inputs were at zero.

Figure 7: Level-Shifting using Potential Divider


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The final stage was the design of the complete differential amplifier with resistor values that optimizes

gain to its maximum, ensuring that a zero voltage output it obtained when both inputs are zero and also

that the CMRR is at lowest. The final project was done and measurements, graphs and pictures were

taken.

Pre-LabBefore starting creating the circuit, one must first find all the necessary components and equipment. For

this, a list with all possible vendors/providers was done in order to ensure that all components were

available in market .Also, if any component was needed have all necessary information of many vendors

to find what needed in a matter of minutes through emails or phone calls.

Table 2: Vendors/Providers List

Name Address Phone

number

Website Address Email Address

1 Alltronics.com N/A N/A www.alltronics.com warehouse@alltronics

2 Ebay N/A N/A www.ebay.com N/A3 Farnell N/A N/A http://uk.farnell.com N/A

4 RS Components N/A N/A http://cy.rsdelivery.com N/A

5 Antoniades

Electronics

Ifigeneias str.

2007 Strovolos

22516456 N/A [email protected]

6 Betatech Ltd 12B Griva

Digeni Latsia

22485378 N/A [email protected]

7 Bionic Diomedous 3

Nicosia

77772060 www.bionic.com.cy [email protected]

8 Pouroutos

Electronics

2 Katsonis str.

Nicosia

22664163 www.pouroutos.com.cy [email protected]

9 OC electronics 4 Kon/nou str.Latsia

22484609 www.ocelectronics.com [email protected]

10 Videotronics 13 Ifigeneias

str. Nicosia

22496898 N/A N/A

Equipment List

In order for all experiments to be done and measurements to be taken many tools were needed.

Table 3: Equipment List

Equipment Type Brand Model Serial Number1 DC Power Supply Gwinstek GPS - 3303

2 Function Generator GW GFG 8020G

3 Function Generator GW GFG 8020G

4 Multimeter - Voltmeter Dagatron TRUE RMS 8511

5 Multimeter - Voltmeter Dagatron TRUE RMS 8511

6 Oscilloscope Gwinstek GDS - 1042


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Components List

In order to complete all stages, necessary circuits and finally build the differential amplifier, some

components were needed

Table 4: Components List

Type Value / Model Quantity

1 Prototype Breadboard ------------ 1

2 Resistor 1M 5

3 Resistor 10 5

4 Resistor 1 5

5 Resistor 4,7 5

6 Resistor 22 5

7 Resistor 1,4 5

8 Resistor 3,3 5

9 Resistor 600 5

10 Resistor 510 511 Resistor 8,2 5

12 Resistor 460 5

13 Zener Diode 2,7 v 1

14 Zener Diode 5,1 v 1

15 Zener Diode 15 v 1

16 Diodes IN4148 4

17 IC Socket N/A 1

18 Integrated Circuit CA3046 1



21 Connection Wire Roll N/A 1

Equations

In table below all necessary equations, for the calculations of measurements taken, are given.

Table 5: Equation Table

Equation Used for

1 Vout=Av(V1) Output Voltage with the gain

2 Ie1=Ie2=Iet/2 Finding current

3 Vc1=Vc2=Vcc-Ic.Rc Finding Voltage

4 Av=Vout/Vin= Rc/2re Finding Gain

5 Zin=2re

6 Vout=ic.Rc Finding Output Voltage through re and current

7 Vin=ie.re+ie.re=2iere Finding Input Voltage through re and current

8 CMRR=Av (mid band)/Av(CM) Common Mode Rejection Ratio

9 Av(CM)=Rc/2Re Gain of Common Mode

10 re=25Mv/Ie Finding re


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Lab Work

Day 1

Section A BreadboardFirst day started with familiarization of the prototyping breadboard. The breadboard has, on two sides,

left and right, two columns that all pin-holes on each one is connected together to all other of the same

column. These columns are used for positive and negative (ground) of the circuit. Also there are many

rows that have 5 pin-holes each, that they are connected together like having a connection wire to

connect components to it. In the middle of the breadboard a small gap exists that is used for being able

to connect IC (integrated circuits) on the breadboard (fig.8).

Figure 8: Prototyping Breadboard

Section B How components get connected to breadboard

Then the connection of components started taking place. A thing one has to consider, is to be sure that

if has the need to connect one component to the breadboard, the components two legs must never be

inserted in the same row because it is like short-circuit the component. Knowing this very importantidea and how the breadboard works, all components were connected for the creation of the first circuit,

after following the schematic circuit created on Multisim based on the books example (fig.9).

Figure 9: Stage1 - Multisim


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Section C Power Supplies

To fulfill the circuits needs, both positive (+15V) and negative (- 15V) had to be ready for use. To

achieve this, the connection of the pins from the power supplys output had to be inserted the other

way around for the negative voltage. So from one output the power supply was connected to the

positive 15 voltage (red output) and the ground and the other output from the negative (black output)

and the ground. After experimenting with the power supplies, the result was that the need, of both

positive and negative voltage from the same source, was fulfilled.

Section D What to Know Before Powering On

On the breadboard, the positive column on the left (red bar) is used for the amplifiers input signal,

signal coming from the frequency generator.

On the breadboard, the positive column on the right (red bar) is used for the power supply of positive

(+15V).

On the breadboard, negative column on the left (blue bar) is used as the ground of the circuit. All

grounds (black cables) must be connected here.

On the breadboard, the negative column on the right (blue bar) is used for the power supply of negative

(-15V).

Results Day 1

Results could not be found from this experiment and measurements could not be taken because the 1

M resistors connected across each component of the circuit are too large to allow results (fig.10).

Figure 10: Circuit - Stage 1


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Day 2

Section A ICs socket

A new socket had to be bought, because as it seemed, the ICs socket we had were not of good quality

(fig.11) and could not be inserted to the breadboard and stay connected to the pin-holes. Every little

while the IC got disconnected and results could not be measured. As it seems, there are two kinds of ICsockets. The ones with the straight pins and the others (better quality)that have a small head on top of

each pin that lead to a better and more stable fit in the breadboards pin-holes.

Figure 11: Left - Low Quality IC Socket / Right - High Quality IC Socket

Section B Procedure

The connection of the circuit was done once again following the schematic circuit created in Multisim.

The connection of the two oscilloscopes probes followed, by connecting each one to the input and

output of the circuit to measure the two values. Both grounds were connected to the necessary ground

pin of the breadboard. Then a parallel connection to both power supplies was done in order to ensure a

voltage +15V and -15V. The multi-meters grounds were also connected to the breadboards ground.

Finally the connection of the signal generator was done in order for the circuit to have an input signal to

amplify (fig.12).

Figure 12: Stage 1 Lab-Work


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Section C Table of Measurements

Table 6: Measurements - Circuit 1

Frequency Vin Vout

1 1kHz 30mVpkpk 2,84Vpkpk

2 5 kHz 30mVpkpk 2,84Vpkpk

3 10 kHz 30mVpkpk 3Vpkpk






9 1 MHz 30mVpkpk 760mVpkpk

10 1,5 MHz 30mVpkpk 480mVpkpk


DC and AC analysis of the circuitVcc=+15v Vee=-15v Re=Rc1=Rc2=4,7

Vin1=30mVpkpk Vout=3 Vpkpk frequency=10 KHz

It=15v/4,7=3,2mA Ie1=Ie2=3,2mA/2=1,6mA

Av=3Vpkpk/30mVpkpk=100 Av(CM)=4,7 /(2X4,7 )=0,5

CMRR=100/0,5 =200 re=25mv/Ie=25mv/1,6mA=15,6 Zin= 9,3

Results Day 2

By having an input of 30mV pk-pk (the lowest possible output of the labs function generator) an output

of 3V pk-pk happened. That meant for a gain of 100 that is a very good result for the first circuit (fig.13).

Figure 13: Stage 1 - Input / Output


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Day 3

Section A Zener Diode

In this circuit a Zener diode was used. This Zener diode has positive and negative side and both have to

be connected properly in order for the correct functionality of the circuit but also for the proper

functionality of Zener diode. If the Zener diode is connected the other way around it may be burned.The Zener diode has a black or blue ribbon around one end. That end is the cathode of the Zener and

the other end in the anode. In our case the cathode was connected to a resistor and then to the ground

and the anode to the supply voltage of -15V.

Section B Procedure

The connection of the circuit was done once again following the schematic circuit created in Multisim

(fig.14). The same connections as the previous circuit took place but with the difference that this circuit

had also the current source circuit connected to it. Another transistor from our IC was used and to it a

Zener diode and two resistors were connected. An improvement on the CMRR and the voltage gain is

expected.

Figure 14: Stage 2- Multisim


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Frequency Vin Vout

1 1kHz 30mVpkpk 3,52Vpkpk











DC and AC analysis of the circuitVcc=+15v Vee=-15v Rc2=4,7 Rb=1,5K Re=3,3 K zener=15v

Vin1=30mVpkpk Vout= 3,60Vpkpk frequency=10 KHz

It=15v/1.8=8,6mA Ie1=Ie2=8,6mA/2=4,3mA

Av=30Vpkpk/3,60mVpkpk=120 Av(CM)=4,7 /(2X1,8 )=1.3

CMRR=120/1,3 =92 re=25mv/Ie=25mv/4,3mA=5,81 Zin= 3,5

Results Day 3

By connecting the current source to the circuit and by having 30 mV pk-pk as an input, the output foundto be 3.6V pk-pk. That meant a gain of 120 that is a good gain. Also the gain of this stage is 20 more than

the previous and that meant that we had a growth of gain as expected (fig.15).



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Day 4

Section A Level Shifting

In this circuit level shifting was used. A level shifting is used so if 2 input signals exist their output should

be equal to their difference. A differential amplifier must have an output equal to zero instead of some

positive potential.

Section B Procedure


The same connections as the previous circuit took place but with the difference that this circuit had also

a level shifting circuit. The level shifting was done by adding another resistor between the differential

amplifier and the current source. Also another signal generator was used, at 10 KHz, to provide the

second input signal (fig.16).

Figure 16: Stage 3 - Multisim


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Section C Measurements

Measurements taken in this stage found all output to be at zero as it should be. By adding the other

signal generator the two inputs were added together resulting in zero output.

DC and AC analysis of the circuit

Vcc=+15v Vee=-15v Rc2=4,7 Rb=1,5K Re=3,3 K zener=15v

Vin1=0Vpkpk Vin2=0Vpkpk Vout= 6,2Vpkpk frequency=10 KHz

R1=1M

Results Day 4

By connecting the level shifting to the circuit, instead of having a minor positive potential the addition of

the two input signals were at perfect zero output (fig.17).



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Day 5

Section A Final Stage

This was the final stage of the amplifier. The perfect amplifier was ready after this stage. To achieve this

all resistors were changed so that the circuit has the maximum gain. Also, the common mode gain is at

the lowest and if two inputs were connected to the differential amplifier the output would be equal tozero.

Section B Procedure


The same connections as the previous circuit took place but with the difference that this circuit had all

resistors were changed so that the final gain would be even greater than previous stages (fig.18).

Figure 18: Stage 4 - Multisim


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Frequency Vin Vout

1 1kHz 30mVpkpk 5Vpkpk








9 1 MHz 30mVpkpk 1,1Vpkpk



DC and AC analysis of the circuitVcc=+15v Vee=-15v Rc2=8,2 R1=600 R3=1,5K R4=510

Zener=15v

Vin1=30mVpkpk Vout=5,2Vpkpk frequency=10 KHz

It=15v/1,7=8,8mA Ie1=Ie2=8,8mA/2=4,4mA

Av=5,2Vpkpk/30mVpkpk=173 Av(CM)=8,2 /(2X1,7 )= 2,41

CMRR=173/2,41 = 72 re=25mv/Ie=25mv/4,4mA=5,7 Zin= 3,4

Results Day 5

After changing all the resistors to necessary values so that the final gain is even greater than before the

final stage of the differential amplifier was complete allowing us to build the perfect differential

amplifier. Having the maximum gain, low common mode gain and zero output when differenciating the

input of two signals. The given input was 30mV Pk-pk and the output was 5.2V pk-pk giving the gain of

173, a lot more than the previous circuit (fig.19).



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Final Result Presentation to ClientThe goal was to create a differential amplifier that consistent of 4 stages. The voltages provided were of

positive +15V and negative15V. The first stage was the simple amplifier using only 2 transistors some

resistors and an input signal that would be amplified. The 10 KHz, 30mV pk-pk signal was amplified with

a gain of 100 and had an output of 3V. The next stage was to connect a current mirror stage, by

replacing the emitter resistor with a current source. By doing this an improvement of the CMRR would

be achieved but also a greater gain. The 10 KHz, 30mV pk-pk signal was amplified with a gain of 120 and

had an output of 3.6V. The stage that followed was an experimental stage to see if by connecting

another input the differential amplifier would differentiate the two inputs and have an output of zero.

To achieve the total zero, a level shifting circuit had to be connected. After this was done, by adding

another input the differential amplifier had an output of a perfect 0. One more step was done to get

closer to the perfect differential amplifier. After changing all the necessary resistors to values that would

give to the differential amplifier even more gain, the final stage of the project was done. A differential

amplifier with low common mode gain, two connections of inputs equal to zero and a great

amplification was ready. By connecting the input of 10 KHz, 30mV pk-pk signal to the proper position of

the breadboard, the positive and negative 15V, the two probes of the oscilloscope and all the grounds to

the ground of the breadboard the amplifier all were ready to see the great amplification. By measuring

the output from the oscilloscope found to be 5.2V. That means the differential amplifier is having a gain

of 173. The project is ready for work.

Differential Amp Report

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