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King Abdul-Aziz University

Faculty of Engineering

Electrical Engineering Department

Biomedical Engineering Primer (EE 370)

Lab Experiment # 1 : (characteristics of an Op Amp)

Fall, 2016                         Section: GA

Team # 2 Name ID

Member # 1 AHMED SMODI 1414541

Member # 2 WADEI MOHMMAD 1207196

Member # 3 MOHMMAD NOFAL 1408194

Member # 4 SAMER ALI ALSHUAIBI 1207554

Under the supervision of: Dr. Bandar Hakim

Lab Instructor: Eng. Ahmed Basheer

Introduction

This report explains the principles of the use of electrical appliances with OP Amp and the characteristics of it, will be concatenated steps of writing the beginning of the main goal of the experiment. Then the information will recall the tools used for this experiment. Then we will remind steps work experience and results. In the end, we will discuss and conclude the final results of the report.

Objectives and the aim for each part of the experiment

In this lab we completed four steps on the OP Amps 741 and 071 to measure and to know the different and the limitation between the ideal OP Amps 741 ,071 and the non-ideal. The first step in this lab is to measure and analyze the linear range limitations of an OP amps that we have it in the Lab, and to compare the data analyst that we got in the lab with the ideal one. The second step in our lab to know the offset voltage of an OP Amps in this step we got the offset between the inverting and non-inverting input of our OP Amps and compare it with the ideal one which has to be zero. The third step was about input bias current of an OP Amps and we have to know the current that enters the input terminals in the OP Amps which has to be zero in the ideal one. The fourth step is about Gain-Bandwidth product (GBW) of an Op Amp in this experiment we have to know the range of the frequency that will not affected the voltage output. So, the aim of this experiment is to know about the most important AC and DC characteristics of any Op Amp by measure them which are rang limitations, Gain-Bandwidth, input bias current, offset voltage.

We can do this approach to arrive at the presented design from the requirements and to satisfy our experiment

Be careful while connecting the devises and the wires.

Take the tools that we need it and keep away the others.

Keep the power off until you make sure all the connections are good.

Keep all liquids away from the devises.

Ask the engineer if there is unexpected.

Connect all the wires of the devises in a stable way.

Put bake each tool that you use it and switch off all the electrical equipment.

Linear range limitations of an Op Amp

Design concept/ the experimental procedure

When we start this step we first got some information about the linear limitations first to do the experiment in a good way. The liner range limitation is the limit of the output of the OP Amp and after this limit will enter the saturation region of the OP Amp. The OP Amp is controlled by +-Vcc so any signal greater than this will affect the output amplitude and get in the saturation region. When we got enough information about the linear limitations we started working on the design of the experiment. We design the task by searching about the best circuit that will be good to the requirement of this step and to help us to reach to best result. We take the suitable resistors to measure the linear limitation and to reach to the exact result of the limitation of the two OP Amps that we use it 741 and 071.

The experimental procedure

We follow this procedure to complete and finish this step in our lab:

We design the circuit of the experiment figure (1).

We take two resistors the first one is 100 ohms the second one is 1k ohm.

We connect the OP Amps 741 and 071 to the bread board each one alone.

We connect the terminals of the OP Amps.

Leg number 7 to the positive 12 volte and 4 to the negative 12 volte.

Leg number 2 to the function generator with 100 ohm resistor between them.

Leg number 3 to the ground.

Leg number 6 witch is the output we connect it to resistor 1 k and with the leg 2.

We connect the oscilloscope to the input leg number 2 and to the output leg number 6.

We put an input range of a voltage amplitude to see the output range and when it will start the saturation region of the two OP Amps on the oscilloscope and the final connection below as shown in figure (2).

Figure(1): circuit for linear limitation of the OP Amp

Bill of material for this experiment

1-Amplifier op amp 741 and 071.

2-Resistors 1K', 100'.

3-Wires.

4- Breadboard.

Lab equipment/accessories needed

1-Function generator.

2-DC power supply.

3-Oscilloscope.

4- Multimeter.

Figure (2): final connection of the linear limitation

Results and the analysis for linear limitation

Table 1: the output of the 741 OP Amp linear range

Input output

1.1 volte at the positive region 10 volte at the positive region

1 volte at the negative region 9.8 volte at the negative region

Table 2: the output of the 071 OP Amp linear rage limitation

Input output

0.92 volte at the positive region 9 volte at the positive region

0.86 volte at the negative region 8.2 volte at the negative region

Figure 4: output for 071 OP Amp                     Figure 3 : output for 741 OP Amp

Conclusion for the linear limitation

Finally, after we done this step we took this results of the two OP Amp that in the table above 1,2. We take the result of the range limitation of the OP Amp by increasing the amplitude until we see the wave on the oscilloscope start in the saturation region and we record that as seen in the tables 1 and 2 and figures 3 and 4.

Input offset voltage

Design concept:

Ideally, the op amp output voltage should be equal zero volts. To obtain that it must to  applied a small differential voltage between the positive and negative terminals. This voltage known as the input offset voltage "Vos" [2].

Input offset voltage is designed as a voltage source in series with the input terminal in inverting op amp, as shown in the figure 5 [3].

Experiment procedure:

We built the circuit using u741 and u071 OP Amps each one alone, we connect the legs of the OP Amps same as in the previews step put here we didn't use a function generator with the input as show in figure 6,7. We connect the resistors which is equal to 100k,100 and 100 Ohms, then we use the digital multimeter "DMM" to measure the output voltage.

Calculation table:

we calculate the output voltage and then we got this results for voltage offset:

Table 3: offset result for 741 OP Amp

Op Amp 741

Vo= 1.4 v

Vos= 1.4 mv

Table 4: offset result for 071 OP Amp

Op Amp 071

Vo= 80 mv

Vos= 80 ''v

Bill of material for each part:

Amplifier op amp 741,071.

Resistors 100', 100', 100k'.

Wires.

Breadboard.

Lab equipment/accessories needed for each part:

DC power supply.

Multimeter.

Conclusion for v offset

After we finished this step we got the offset as shown in the tables above 3,4 we calculate the offset for each OP Amp by dividing the v out on the gain that we got it from the resistors as we see here the gain equal 1000. We got the gain by dividing the RF which is 100000 over RI which is 100.

Figure 6: circuit for v offset

Figure 7: connection for v offset

Input bias current

Design concept:

Ideally, there is no current flows into the input (positive & negative) terminals, but in practice there is a different situation, there are two input bias current (IB-) and (IB+), as shown in figure 7. The value of the current in the terminals are different and depends on the type of the op amp, usually between Ampere and Microampere [4].

Experiment procedure:

we connect the circuit as shown in figure 7 we used three different value of resistor 100k, 100,100 ohms to measure the current the follow in the resistor 100-ohm witch is between leg two and the other 100-ohm resistor that is called bias current.

Calculation tables

Table 5: the result of the input bias current

 Op Amp u741 V1= 1.4 mV

Vo= 1.4 V

If= 13.9 ''A

I2= 14 ''A

I1= 0.1 ''A

Table 6: the result of the input bias current

 Op Amp u071 V1= 0.1 mV

Vo= 77 mV

If= 77 ''A

I2= 1 ''A

I1= 769 ''A

Conclusion for bias current

we calculate the bias current and record the result as shown in the tables above 5,6. After we connect the circuit of the bias current with three resistors we got the v out and the v1 which is between the two resistors 100 and 100 ohms. After we got the two voltages we calculate the bias current by these formulas. If=I1+I2        IF=(VO-V1)/100K    I2=V1/100.

The If current which flow over the resistor 100k ohm and I2 the bias current I1 the current flow over the other 100 ohms resistor.

Circuit design

Figure 7: connection for bias current

Bill of material bias current

1-Amplifier op amp 741.

2-Resistors 100K', 100', 100'.

3-Wires.

4- Breadboard.

Lab equipment/accessories needed for each part

1-DC power supply.

2-multimeter.

Gain-Bandwidth product (GBW) of an Op Amp/ Design concept

When we start working on the gain bandwidth product, we first define it then we design the most suitable circuit for the (GBP). "For any devices such as operational amplifiers that are designed to have a simple one-pole frequency response, the gain'bandwidth product is nearly independent of the gain at which it is measured; in such devices the gain'bandwidth product will also be equal to the unity-gain bandwidth of the amplifier (the bandwidth within which the amplifier gain is at least 1). For an amplifier in which negative feedback reduces the gain to below the open-loop gain, the gain'bandwidth product of the closed-loop amplifier will be approximately equal to that of the open-loop amplifier. According to S. Srinivasan, "The parameter characterizing the frequency dependence of the operational amplifier gain is the finite gain'bandwidth product" [1]. So the (GBP) in any amplifier is one of the characteristic of that OP Amp which can be designed by the manufacture of that OP Amp. The (GBP) is related to the frequency of the input amplitude to the OP Amp and how it is effected by that frequency and what is the range of it before it starts to reduces the output amplitude. We design a circuit to do the experiment and to reach to exact requirements we take two resistors one is 100k ohm and 10k ohm to get a small gain equal to 10. Look at the graph of the OP Amps 741 and 071 of the (GBP) rang with the frequency to compare it with the non-ideal one as shown in the figure below 8. After this we connect the circuit as shown in figure below 9.

Figure 8: the gain band width product for OP Amp 741

Figure 9 : circuit for (GBP) connection

The experimental procedure

Build the circuit in Figure 9,10 by using 741 Op Amp, and we plug it in the bread board with two resistances RF and RI which are equal to 100K' and 10K' respectively.

We connect the OP Amp legs.

Leg 2 to the function generator and 10k ohm between them.

We put the function generator at 10 mv to not exceed the saturation region.

We put +_ 12 on each leg 7 and 4 respectively.

Connect leg 3 to the ground.

Connect leg 6 with the input leg number 2 and in the output with 100k ohm.

Now we can take the output signal from leg number 6 by the oscilloscope.

Bill of material for each part for (GBP)

1-Amplifier op amp 741 and 071.

2-Resistors 10K', 100'.

3-Wires.

4- Breadboard.

Lab equipment/accessories needed for each part

1-Function generator.

2-DC power supply.

3-oscilloscope.

4- Multimeter.

Results and the analysis (GBP)

Table 7: the output of the (GBP) for 071 OP Amp

Input frequency (Hz) Gain Does the voltage reduce GBP

100 10 No 10*100=1000

200 10 No 10*200=2000

1000 10 No 10*1000=10000

5000 10 No 10*5000=50000

20000 10 No 10*20000=200000

30000 10 No 10*30000=300000

40000 10 Yes 10*40000=400000

Table 8: the output of the (GBP) for 741 OP Amp

Input frequency (Hz) Gain Does the voltage reduce GBP

200 10 No 10*200=2000

5000 10 No 10*5000=50000

15000 10 No 10*15000=150000

22000 10 yes 10*22000=220000

700 1000 yes 1000*700=700000

Figure 10 :  the connection for (GBP)

Conclusion for (GBP)

We finished this step by doing the procedure carefully to reach to the final result. In this experiment we use two OP Amps 741 and 071 as shown in the tables 7,8 above. As the tables illustrates we change the resistors to change the gain for better reading and to get exact curve of wo OP Amps. In this experiment first we take a range of frequency from low to high frequency until the amplitude reduces we record that after that we get the GBP by multiply the gain with the frequency that changed the voltage amplitude. As shown in the table 7 the amplitude changed on 40k HZ with 10 gain, also table 8 shows that the amplitude changed on 22000 HZ with 10 gain and 700 HZ with 1000 gain. After we got this information we can compare it with the ideal one of the OP Amps curve.  

Conclusion

 At the end of this report, we have learned a lot, especially about the characteristics of OP Amps. Also, we have learned how to find the Op Amp 741 and 071 characteristics in the lab, how can we apply some basic methods to obtain the  linear range limitations , the input bias current , the offset voltage also the gain-bandwidth product (GBW) of an Op Amp.

Through this report, we have explained the objectives of the experiment. Then showing the tools used in it. After that, we explained the theoretical information about the methods used in this experiment. Then we showed the procedure that followed through this experiment step by step until we got our final results, and finally commented on our results. This experiment was great opportunity for the team to improve the performance.

References

[1]- Srinivasan, S. "A universal compensation scheme for active filters." International Journal of Electronics 42.2 (Feb. 1977): 141. Science & Technology Collection. EBSCO. Dallas Public Library <http://www.dplibrary.org>, Dallas, TX, USA. retrieved 31 July 2009 from <http://search.ebscohost.com/login.aspx?direct=true&db=syh&AN=5259750&site=ehost-live>.

[2] Richard Palmer, DC Parameters: Input Offset Voltage (VIO), Taxes, 2001.

*Site link: [http://www.ti.com/lit/an/sloa059/sloa059.pdf]

[3] Analog Device company.

*Site link: [http://www.analog.com/media/en/training-seminars/tutorials/MT-037.pdf?doc=CN0326.pdf]

 [4] Analog Device, Op Amp Input Bias Current.

*Site link: [http://www.analog.com/media/en/training-seminars/tutorials/MT-038.pdf?doc=CN0326.pdf].

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