UNIVERSITI MALAYSIA PERLIS
ANALOG ELECTRONICS II
EMT 212
EXPERIMENT # 4
OP-AMP (COMPARATOR BASICS)
MARKS
G1
G2
G3
G4
G5
4
2
4
2
4
G6
G7
G8
Q
C
2
4
2
10
10
NAME
signature
MATRIK #
Total
100%
44
PROGRAMME
GROUP
DATE
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
EXPERIMENT 4
Op-Amp (Comparator Basics)
1.
OBJECTIVE:
1.1
To demonstrate the op-amp zero reference inverting comparator
1.2
To demonstrate the op-amp negative reference inverting comparator
1.3
To understand the op-amp negative reference non-inverting
comparator
1.4
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 noninverting 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.
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Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Vout
VCC
+15V
+15
Positive
saturation
7
+10
Vin
2
-
3
+5
6
Vout
Vin
+
-15 -10
-5
+5 +10 +15
-10
4
Vref
-5
Negative
saturation
VCC
-15
-15V
(a) Circuit
(b) Transfer curve
Figure 2.2: Transfer Characteristic Curve
3.
COMPONENT AND EQUIPMENT:
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
Resistors:
3.1.1 100 k
3.1.2 10 k
Variable resistor
3.2.1 1 k
Zener diode
3.3.1 5.6 V
LM 741 OP-AMP
DC Power Supply
Function Generator
Oscilloscope
Breadboard
Voltmeter
4.
PROCEDURE:
4.1
Figure 4.1 shows the schematic of zero reference inverting comparator.
Apply a 500 Hz, 3V pk sinewave input signal to the circuit. Set both channels
to gnd and position the zero references using the vertical adjust. Record the
Vout waveforms on Graph 1. Set the oscilloscope to the X-Y mode and record
the output-input voltage transfer characteristic on Graph 2.
CH1
+15V
CH2
Vin
~
741
+
-15V
CH1 gnd
CH2 gnd
Figure 4.1 The schematic of zero reference inverting comparator
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Analog Electronics II (EMT212) 2007/2008
Laboratory Module
4.2 Figure 4.2 shows the schematic of negative reference inverting comparator.
Apply a 500 Hz, 3V pk sinewave input signal to the circuit. Set Vref , the DC
reference, at -2 V by adjusting RV. Then set both channels to gnd and position
the zero references using the vertical adjust. Record the Vout waveforms on
Graph 3. Set the oscilloscope to the X-Y mode and record the output-input
voltage transfer characteristic on Graph 4.
-15V
10kΩ
+15V
CH1
CH2
-
741
+
(to +ve terminal
RV , 1kΩ
Vref
Vin
~
Vout
-15V
Vref
CH2 gnd
CH1 gnd
Figure 4.2 The schematic of zero reference inverting comparator
4.3
Figure 4.3 shows the schematic of negative reference non-inverting
comparator. Apply a 500Hz, 3V pk sinewave input signal to the circuit. Set
Vref , the DC reference, at -2 V by adjusting RV. Then set both channels to
gnd and position the zero references using the vertical adjust. Record the
Vout waveforms on Graph 5. Set the oscilloscope to the X-Y mode and record
the output-input voltage transfer characteristic on Graph 6.
10kΩ
-15V
+15V
CH1
+
741
Vin
~
(to –ve terminal)
RV,1kΩ
Vref
CH1 gnd
-
Vref
-15V
CH2
Vout
CH2 gnd
Figure 4.3 The schematic of negative reference non-inverting comparator
4.4
Figure 4.4 shows the schematic of op-amp comparator plus positive output
bounding. Apply a 500Hz, 3V pk sinewave input signal to the circuit. Set
both channels to gnd and position the zero references using the vertical
adjust. Record the Vout waveforms on Graph 7. Then set the oscilloscope to
dc and the X-Y mode and record the output-input voltage transfer
characteristic on Graph 8.
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Analog Electronics II (EMT212) 2007/2008
Laboratory Module
DZ = 5.6V
5.6 V
+15V
100kΩ
CH1
- 741
R2
Vin
~
CH2
+
-15V
Vout
CH2 gnd
CH1 gnd
Figure 4.4 The schematic of op-amp comparator plus positive output bounding
5
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Matric No.
: _______________________________
RESULTS:
output
voltage
input
ZERO REFERENCE INVERTING COMPARATOR
time
4 marks
Graph 1
ZERO REF COMPARATOR CHARACTERISTIC
16
12
output voltage
5.
Date : _______________
8
4
0
4
8
12
16
5
4
3
2
1
0
1
inputGraph
voltage 2
6
2
3
4
5
2 marks
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Matric No.
: _______________________________
Date : _______________
output
voltage
input
NEGATIVE REF INVERTING COMPARATOR
time
Graph 3
4 marks
16
NEGATIVE REF COMPARATOR CHARACTERISTIC
output voltage
12
8
4
0
4
8
12
16
5
4
3
2
1
0
1
2
3
4
5
input voltage
Graph 4
2 marks
7
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Date : _______________
Matric No.
: _______________________________
output
voltage
input
NEGATIVE REF NON-INVERTING COMPARATOR
time
4 marks
Graph 5
-VE REF NI COMPARATOR CHARACTERISTIC
16
output voltage
12
8
4
0
4
8
12
16
5
4
3
2
1
0
1
2
3
4
5
input voltage
2 marks
Graph 6
8
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Date : _______________
Matric No.
: _______________________________
output
voltage
input
ZERO REF +VE BOUND INV COMPARATOR
4 marks
time
Graph 7
ZERO REF +VE BOUND INV COMP TF
8
output voltage
7
6
5
4
3
2
1
0
1
5
4
3
2
1
0
1
input voltage
Graph 8
9
2
3
4
5
2 marks
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Matric No.
: _______________________________
6.
Date : _______________
QUESTIONS:
mark
Q1
What is comparator?
A1
Q2
(2)
State the function of a comparator
A2
Q3
(2)
How does the comparator (no) hysteresis perform as a waveform generator (sine input)?
A3
(2)
Q4
A4
How to determine the reference voltage of a comparator?
(2)
Q5
What does the voltage gain of comparator equal?
A5
(2)
10
Analog Electronics II (EMT212) 2007/2008
Laboratory Module
Name
:_____________________________
Matric No.
: _______________________________
7.
Date : _______________
CONCLUSION (10 marks)
Based on this experiment, state the purpose served by a comparator.
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