UNIVERSITI MALAYSIA PERLIS

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1 UNIVERSITI MALAYSIA PERLIS ANALOG ELECTRONICS II EKT 214 Semester II (2013/2014) EXPERIMENT # 4 OP-AMP (COMPARATOR BASICS)

2 EXPERIMENT 4 Op-Amp (Comparator Basics) 1. OBJECTIVE: 1.1 To demonstrate the op-amp zero reference inverting and non-inverting comparator 1.2 To understand the op-amp comparator + positive output bounding 2. INTRODUCTION: A comparator is a special type of op amp that is used to compare the voltages of the two inputs. A basic comparator circuit is operated without a feedback loop. When one input of the comparator is at a reference potential, the output will indicate whether the unknown voltage at the other input is higher or lower than the reference. Figure 2.1 : A Comparator 2.1 The Transfer Characteristic Curve A comparator also is a switching device that produces a high or low output, depending on which of the two inputs is larger. The comparator is run with the very high open-loop gain. When the non-inverting input is very slightly larger than the inverting input, the output goes to positive saturation; otherwise it goes to negative saturation. Although general-purpose op-amps can be used as comparators, specially designed op-amps can switch faster and have additional features not found on general-purpose op-amps. For noncritical applications, general-purpose op-amps are satisfactory and will be used in this experiment. A comparator circuit is characterized by its transfer characteristic. The transfer characterictic (curve) is a plot of the output voltage (plotted along y-axis) as a function of the input voltage (plotted along the x-axis). Consider the comparator shown in Figure 2.2 (a). The reference voltage is -6V. When the input is greater than +6.0 V, the output will go to positive saturation (approximately +13 V); when the input is less than +6.0 V, the output will be in negative saturation. A glance at the transfer curve will show the output for any given input voltage. 1

3 4 7 Analog Electronic II (EKT 214) 2013/2014 VCC +15V V out Vin Vref Vout Positive saturation V in VCC -15V Negative saturation -15 (a) Circuit (b) Transfer curve Figure 2.2: Transfer Characteristic Curve 3. COMPONENT AND EQUIPMENT: 3.1 Resistors: k 3.3 Zener diode N LM 741 OP-AMP 3.5 DC Power Supply 3.6 Function Generator 3.7 Oscilloscope 3.8 Breadboard 2

4 4. PROCEDURE: 4.1 Figure 4.1 shows the schematic of zero reference inverting comparator. Apply a 5 khz, 5V pk sinewave input signal to the circuit. Set both channels at the position, zero references using the vertical adjust. Record the V out waveforms on Graph 1. Record the output-input voltage transfer characteristic on Graph 2. Figure 4.1 The schematic of zero reference inverting comparator 4.2 From Figure 4.2 shows the schematic of zero reference non-inverting comparator. Apply a 5 khz, 5V pk sinewave input signal to the circuit. Set both channels at the position, zero references using the vertical adjust. Record the V out waveforms on Graph 3. Record the output-input voltage transfer characteristic on Graph 4. Figure 4.2 The schematic of zero reference non-nverting comparator 3

5 4.3 Figure 4.3 shows the schematic of op-amp comparator plus positive output bounding. Apply a 5k Hz, 5V pk sinewave input signal to the circuit. Set both channels at the position, zero references using the vertical adjust. Record the V out waveforms on Graph 5. Then, record the output voltage transfer characteristic on Graph 6. Figure 4.3 The schematic of op-amp comparator plus positive output bounding 4

6 UNIVERSITI MALAYSIA PERLIS ANALOG ELECTRONICS 2 EKT 214 EXPERIMENT # 4 OP-AMP (COMPARATOR BASICS) SEMESTER II (2013/2014) NAME PROGRAMME GROUP MATRIK # DATE MARKS G1 G2 G3 G4 G5 G6 Q C total %

7 5. RESULTS: 3 marks Graph 1 2 marks Graph 2 6

8 3 marks Graph 3 2 marks Graph 4 7

9 3 marks Graph 5 Graph 6 2 marks 8

10 6. QUESTIONS: (7 marks) 1) What is comparator? 2) State the function of a comparator. 3) Describe the operation of zero reference inverting and non-inverting comparator. 7. CONCLUSION ( 5 marks) Based on this experiment, state the purpose of a comparator. 9