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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