Download Functions Generator

FUNCTION GENERATOR WITH OP-AMP
I. OBJECTIVES
a) To determine the domains for the amplitude and frequency of the
rectangular, triangular and sinusoidal generated signals.
II. COMPONENTS AND INSTRUMENTATION
We use the experimental assembly in Fig. 4. For the differential
supply we need a dc voltage source. We will visualize the voltages in the
circuit using a dual channel oscilloscope.
III. PREPARATION
P1. Rectangular and triangular signal generator with Op-amp
 For the circuit in Fig. 1., what is the function of the U1A operational
amplifier and the role of the Q1Q3 group, connected at the output?
 What are the amplitudes of the voltages in the OutD and Dreptunghi
points, if it is known that the Q1Q3 group acts like two DZ 7V5, connected
anode to anode, and J9 - J10 and J11 - J12 are not connected? Draw the two
waveforms.
 For the circuit in Fig. 1., what is the function of the U1B operational
amplifier together with the capacitors on the feedback (alternatively
connected in the circuit)?
 Draw the voltages in the Dreptunghi and Triunghi points, for the
capacitors alternatively connected in the circuit.
 What kind of adjustment does Pot1 do, together with one of the
capacitors C1, or C2?
 Compute the minimum and maximum frequency of the rectangular
voltage (Dreptunghi output) for each of the two capacitors (alternatively
connected in the circuit).
 Compute the value of the fraction k of the Pot1 potentiometer for C1
connected in the circuit for which the rectangular voltage has a frequency of
5KHz?
 Compute the value of the fraction k of the Pot2 potentiometer for C2
connected in the circuit for which the rectangular voltage has a frequency of
10KHz?
P2. Sine wave generator with Op – amp
 What is the function of the circuit in Fig. 2. and the role of the first Op
- amp (U2A)?
 What is the role of the Pot2 potentiometer?
 Draw the voltages from the Triunghi (from the previous exercise) and
Sinus points.
P3. Amplitude adjustment circuit
 For the circuit in Fig. 3. specify the function of the U3B Op - amp.
What kind of adjustment can be done using this circuit (pay attention to the
Pot3 potentiometer)?
 Compute the minimum and maximum values for the gain of the
circuit.
 Compute the minimum and maximum values of the amplitudes of the
rectangular, triangular and sinusoidal signals, from the Out terminal of the Op
- amp (U3B) and the amplitudes of the output signals if k=0.5 (for Pot3).
IV. EXPLORATIONS AND RESULTS
1. Rectangular and triangular signal generator with Op - amp
Exploration
 For the circuit in Fig.1. apply a differential voltage ±15V in the points
J1 and J2.
 Use the jumpers to connect J9 with J10 and visualize on the
oscilloscope the voltages in the OutD and Dreptunghi, Dreptunghi and
Triunghi points.
 Using the Pot1 potentiometer, determine the minimum and maximum
values of the frequency of the rectangular signal (Dreptunghi output).
 Adjust Pot1 in order to obtain a signal with a frequency of 5KHz at
the Dreptunghi output.
 Disconnect J9 from J10, connect J11 with J12 and determine once
again, using Pot1, the minimum and maximum values of the frequency of the
rectangular signal.
 Adjust Pot1 in order to obtain a signal with a frequency of 10KHz at
the Dreptunghi output.
 Disconnect J11 from J12, reconnect J9 with J10 and determine once
again, using Pot1, the minimum and maximum values of the frequency of the
rectangular signal.
R4
22k
R3 27k
Dreptunghi
J9 - J10
C1
2
1
+15
U1A
8
1n
+
V+
3
R5
1
OUT
2
J11 - J12
1
C3
-
470p
V-
2.2k
2
LF412
-15
POT1
4
R1
BC546
4
-15
R6
Q1
OutD
0
6
5k
-
V-
10k
15k
U1B
LF412
Q3
5
+
7
V+
OUT
R7
+15
8
BC546
1k
R2
10k
J1
+15
1
J2
2
1
-15
2
0
0
Triunghi
0
Fig. 1. Rectangular and triangular signal
generator
Results
 The voltages in OutD and Dreptunghi points.
 The voltages in Dreptunghi and Triunghi points.
 The minimum and maximum values of the frequency of the
rectangular signal, for the C1 capacitor (J9 with J10).
 The minimum and maximum values of the frequency of the
rectangular signal, for the C2 capacitor (J11 with J12).
 The value of the frequency of the rectangular signal, using the
capacitor C1 for Pot1 adjusted to obtain frequency of 10KHz using capacitor
C2.
2. Sine wave generator with Op – amp
Exploration
 Disconnect all the jumpers from the circuit.
 For the circuit in Fig. 2 supply the points J1 and J2 with differential
voltage ±15V.
+15
R17
2.2Meg
-15
R20
2.2Meg
R19
39k
R18
390k
R22
R21
390k
D6
39k
R16
12k
D1N4148
D5
R15
100k
D4
D1N4148
R14
270k
D3
R13
12k
D2
D1N4148
Triunghi
2
-
POT2
C2
R9
100n
10k
R10
100k
-15
0
+15
6
-
V-
8
4
+
270k
V+
3
R11
1
OUT
5K
100k
D1
TL062
V-
-15
4
U2A
R12
+15
1
J2
2
1
-15
5
2
+
V+
OUT
J1
R8
7
U2B
TL062
8
+15
10k
0
0
Sinus
Fig. 2. Sine wave generator
 Use the jumpers to connect J9 with J10 and visualize on the
oscilloscope the voltages in the Triunghi and Sinus points.
 Modify the value of the Pot2 potentiometer until the voltage at the
Sinus output is a sine wave and determine its amplitude, from the
oscilloscope.
 Using the Pot1 potentiometer, determine the minimum and maximum
values of the frequency of the sine wave (Sinus output).
 Disconnect J9 from J10, connect J11 with J12 and determine once
again, using Pot1, the minimum and maximum values of the frequency of the
sine wave.
Results
 The voltages in the Triunghi si Sinus points.
 The amplitude value of the sine wave (Sinus output).
 The minimum and maximum values of the frequency of the sine wave
for the capacitor C1 (J9 with J10).
 The minimum and maximum values of the frequency of the sine wave
for the capacitor C2 (J11 with J12).
3. Amplitude adjustment circuit
Exploration
 Disconnect all the jumpers from the circuit.
 For the circuit in Fig. 3. supply the points J1 and J2 with differential
voltage ±15V.
J1
+15
2
2.7k
R25
4k7
-15
OUT
POT3
+
0
R24
5k6
0
Fig. 3. Amplitude adjustment circuit

0
V-
R23
5K
1
Use the jumpers to connect J9 with J10.
V+
J7 - J8
1
1
J5-J6
1
J3-J4
J2
1
2
Sinus
2
Triunghi
2
Dreptunghi
+15
UA741
-15
2
 To modify the amplitude of the rectangular signal, connect J3 with J4.
Visualize the signal from the Dreptunghi and Out points.
 Modify Pot3 (from minimum to maximum) the minimum and
maximum values of the amplitude of the output voltage (Out).
 Check if for Pot3 set at half, you get a value of the amplitude of the
output voltage VOut inside the interval you determined.
 To modify the amplitude of the triangular signal, disconnect J3 from
J4 and connect J5 with J6. Visualize the signal from the Triunghi and Out
points.
 Modify Pot3 (from minimum to maximum) the minimum and
maximum values of the amplitude of the output voltage (Out).
 Check if for Pot3 set at half, you get a value of the amplitude of the
output voltage VOut inside the interval you determined.
 To modify the amplitude of the sinusoidal signal, disconnect J5 from
J6 and connect J7 with J8. Visualize the signal from the Sinus and Out points.
 Modify Pot3 (from minimum to maximum) the minimum and
maximum values of the amplitude of the output voltage (Out).
 Check if for Pot3 set at half, you get a value of the amplitude of the
output voltage VOut inside the interval you determined.
Results
 The voltages in the Dreptunghi and Out points.
 The minimum and maximum values of the amplitude of the output
voltage VOut.
 The value of the amplitude of VOut for Pot3 set at half.
 The voltages in the Triunghi and Out points.
 The minimum and maximum values of the amplitude of the output
voltage VOut.
 The value of the amplitude of VOut for Pot3 set at half.
 The voltages in the Triunghi and Out points.
 The minimum and maximum values of the amplitude of the output
voltage VOut.
 The value of the amplitude of VOut for Pot3 set at half.
REFERENCES
1. Oltean, G., Circuite Electronice, UT Pres, Cluj-Napoca, 2007, ISBN 978973-662-300-4
2. M. Ciugudean, T. Mureşan, H. Cârstea, M. E. Tănase, Electronica aplicată
cu circuite integrate analogice. Dimensionare, Editura de Vest, Timisoara,
1991, ISBN 973-36-0081-4
3. http://www.bel.utcluj.ro/dce/didactic/fec/fec.htm
Fig. 4. Experimental assembly