EEE1046 Electronics III Experiment ECT1
FACULTY OF ENGINEERING
LAB SHEET
ELECTRONICS III
EEE1046
TRIMESTER 3 (2013/2014)
ECT1: Operational Amplifiers
EEE1046 Electronics III
Experiment ECT1: Operational Amplifiers and Their Typical Applications
1.0 Objective
· To understand the basics of integrated circuit (IC) operational amplifier 741.
· To illustrate typical applications of op-amp circuits.
2.0 Apparatus
Equipments required:
a) Oscilloscope.
b) Regulated Power Supply – Two single-output power supplies or a dual-output power supply that could produce positive and negative voltages.
c) Function generator.
d) Digital multimeter.
e) Breadboard, and some single core wires.
Components required (quantities shown within parenthesis):
a) Resistors (0.25W, carbon film) – 10kW (4), 33kW (1)
b) Potentiometer (0.5W or 1W) – 100kW (1).
c) Operational Amplifier (dual-in-line package): 741 (1).
d) Capacitor – electrolytic 10mF/16V (2)
3.0 Introduction
Operational amplifiers are integrated circuits capable of amplification and operation of analog signals (ac or dc). Usually the output of an operational amplifier is the amplification of the difference of the signals at its two input terminals. Internally the op-amp is made up of three basic circuits: a high input impedance differential amplifier, a high gain voltage amplifier and a low impedance output amplifier. These three circuits deal with the three most important characteristics of an op-amp:
1. High input impedance: results in minimal loading and therefore negligible currents produced at the inputs.
2. High open loop gain: provides a wide range of closed loop applications.
3. Low output impedance: gives the ability to drive a wide variety of loads with little effect on the output voltage.
A general purpose IC Op-amp has two input terminals (the inverting or negative input and the non-inverting or positive input), an output terminal, two voltage supply terminals (positive and negative) and terminals for offset adjustments. The 741 is a general purpose integrated circuit (IC) operational amplifier. It is typically housed in an eight-pin plastic package known as plastic dual-in-line (plastic DIP). The assignment of pin functions for 741 is shown in Figure 1.
Figure 1 - Operational Amplifier 741 Pin Diagram.
4.0 Experiments
Instructor’s checks & On-The-Spot Evaluation:
The instructor will check as to whether you have done a proper job before allowing you to proceed to the next experiment. You will be asked to repeat your work if your results are not of a satisfactory level. All results – both displayed (oscilloscope), and sketched (graph), are to be shown to the instructor.
On-The-Spot Evaluation:
On the spot evaluation is individual and will take into consideration of individual commitments towards the experiments such as self-preparation, punctuality, self-initiative, active participation, cooperation, good learning attitude, team work and efforts.
· Students are responsible to ask the instructor to check their experimental results before proceeding to the next experiment.
· On-The-Spot Evaluation will be carried out throughout the experiments to assess the students’ participation and commitments in the experiments.
Note: Circuit is not working but experimental results are correct – Cheating (0 marks)
Circuit construction:
Construct the following circuits using operational amplifier 741 and other circuit elements as shown in the diagrams and follow the procedures outlined for each.
Pins not connected:
In all these experiments, pins 1, 5 and 8 of integrated circuit 741 are left not connected. Pins 1 and 5 are for offset voltage adjustment, of which can be ignored at this stage.
Caution on the oscilloscope:
Make sure the INTENSITY of the displayed waveforms is not too high, as it can burn the screen of the oscilloscope.
Caution on the function generator:
Never short-circuit the output, which may burn the output stage of the function generator.
Oscilloscope setups:
1. Check that all the 3 variable (VAR) knobs are at their calibrated (CAL’D) positions.
2. Set DC input coupling for both channels for all the experiments.
3. Position the channel ground levels as indicated in the lab report form.
4. Set time/div to display one to two cycles of waveforms.
5. Set volts/div for most accurate measurement (at least covering 3.2 vertical divisions).
6. Other settings – as that you have learned in your past experiments in the previous trimesters.
Sketching of the waveforms:
1. Use the waveform sketching technique you learned during Electronics 1 lab experiments (Appendix D). You are assumed to already have the skill.
2. All waveforms must be sketched on the graphs given in the short report form.
3. All waveforms sketched must be as per displayed on the oscilloscope screen.
4. Vout(t) must be sketched with respect to Vin(t).
5. Time/div and volts/div must be recorded.
Positive and negative (with respect to ground) DC voltage supplies:
Method for obtaining positive and negative voltage supplies from two single power supplies is illustrated in Figure 2a.
Figure 2a – Obtaining +10V and –10V from single power supplies
Smoothing capacitors:
These capacitors provide low inductance current paths for high frequency (in MHz) or transient (rising and falling of square waves) signals. They stabilize the voltage at the DC supply voltage lines, and reduce the inductive effect on output waveform distortion. Connect two smoothing capacitors on the breadboard as indicated in Figure 2b and Appendix B. Note that the capacitors are polar type whereby the negative terminal (as indicated on the capacitor casing) must be connected to the lower potential end (otherwise, an explosion may occur).
Figure 2b – Smoothing capacitors on breadboard.
4.1 Inverting Amplifier
Figure 3 – Inverting Amplifier
Procedures
(a) Calculate Vout(pp) [the peak-to-peak voltage of Vout] using the equation below and record in the lab report. Assume that Vin(pp) = 1.0V [Vin(pp) is the peak-to-peak voltage of Vin],
, negative (-) sign indicates 180o phase shift
(b) Construct the circuit as shown in Figure 3 (refer to Appendix B for breadboard connections). Double-check the power supply voltages before connect the power supply outputs to the circuit.
(c) Using a function generator, apply a 1.0V peak-to-peak sine wave of 1 kHz to the input Vin of the inverting amplifier shown in Figure 3.
(d) Set proper time/div and volts/div as mentioned in page 2. Why do we need to set the proper time/div and volts/div? Justify your answer.
(e) Measure Vout(pp) (this measured value should be around the predicted value) and record the phase shift of Vout with respect to Vin (f). Calculate the ratio Vout(pp)/Vin(pp). Sketch the waveforms of Vin and Vout. Interpret the observation of the displayed waveform to the instructor.
(f) Ask the instructor to check all of your results. Show your last oscilloscope-displayed waveforms to the instructor.
4.2 Noninverting Amplifier
Figure 4 - Noninverting Amplifier
Procedures
(a) Calculate Vout(pp) using the following equation (with Vin(pp) = 1.0V):
(b) Construct the circuit as shown in Figure 4. Apply a 1.0V peak-to-peak sine wave of 1 kHz to the input Vin. Measure Vout(pp) and record f. Calculate the ratio Vout(pp)/Vin(pp). Sketch the waveforms of Vin and Vout. Interpret the observation of the displayed waveform to the instructor.
4.3 Buffer
Figure 5 - Noninverting Buffer / Voltage Follower.
Procedures
(a) Construct the circuit as shown in Figure 5. Apply a 1.0V peak-to-peak sine wave of 1 kHz to the input Vin. Measure Vout(pp) and record f. Calculate the ratio Vout(pp)/Vin(pp). Sketch the waveforms of Vin and Vout. Interpret the observation of the displayed waveform to the instructor.
(b) Ask the instructor to check all of your results. Show your last oscilloscope-displayed waveforms to the instructor.
4.4 Quantizer or Comparator
Figure 6a - Op-amp Comparator Circuit (non-inverting).
(Refer to Appendix A for potentiometer (pot) connections.)
Procedures
(a) Solve Vin = Vref to determine the width tw1 and then tw. You are told that: Vin = 0.5sinwt, where w = 2pf and f = 1kHz, and Vref = 0.3V. (Note: p radians = 180o). Calculate tw/T, where T is the time period.
(b) Construct the circuit as shown in Figure 6a. Use multimeter to check the supply voltages are +10V and -10V. Adjust the potentiometer to get Vref = 0.3V (measured by a multimeter at pin 2).
(c) Apply a 1.0V peak-to-peak sine wave of 1 kHz to the input Vin. CH1 and CH2 must use DC input coupling. Set CH2 volts/div to display the whole waveform.
Notes: Function Generator output offset voltage (if any)
Check the function generator output offset voltage (the average voltage) is zero (0V). If not, manually adjust it to zero before measurements.
(d) Measure Vout(+sat), Vout(-sat), T and tW. [Vout(+sat) is the Vout positive saturation voltage. Let tW is the width when Vout = Vout(+sat)].
(e) Calculate tW/T based on the output obtained. Sketch the waveforms of Vin and Vout.
(f) Observe the Vout changes by varying Vref between 0V (at the Y side) and 0.5V (no data recording is required for this observation). Interpret the observation of the displayed waveform to the instructor.
Report Submission
You are to submit your report immediately upon completion of the laboratory session.
End of Lab Sheet
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