AB-45 Operational Amplifier (Schmitt Trigger & Comparators) ANALOG LAB EXPERIMENT BOARD Ver. 1.0

Transcription

1 Operational Amplifier (Schmitt Trigger & Comparators) ANALOG LAB EXPERIMENT BOARD Ver. 1.0 An ISO 9001: 2000 company

2 94-101, Electronic Complex, Pardesipura INDORE , India. Tel.: Fax: Web: Scientech Technologies Pvt. Ltd. 2

3 OPERATIONAL AMPLIFIER (SCHMITT TRIGGER & COMPARATORS) AB-45 TABLE OF CONTENTS 1.Introduction 3 2. Theory 5 3.Experiment 1 10 To study Operational Amplifier As Comparator and Zero Crossing Dectector. Experiment 2 12 To study Operational Amplifier As Schmitt Trigger. 4.Datasheet 14 5.Warranty 15 6.List of Service Centers 16 7.List of Accessories with AB Scientech Technologies Pvt. Ltd. 3

4 INTRODUCTION AB-45 is a compact, ready to use OPERATIONAL AMPLIFIER experimental Board. This is useful for students to study Op-amp as Comparator, Zero crossing Detector and Schmitt trigger. It can be used as stand alone unit with external DC power supply or can be used with SCIENTECH ANALOG LAB ST-2612 which has built in DC power supply, AC power supply, function generator, modulation generator, continuity tester, toggle switches, and potentiometer. List of Boards : Model AB-01 AB-02 AB-03 AB-04 AB-05 AB-06 AB-07 AB-08 AB-09 AB-15 AB-16 AB-17 AB-18 AB-19 AB-21 AB-22 AB-23 AB-25 AB-28 AB-29 AB-30 AB-31 AB-32 AB-33 AB-34 AB-38 AB-41 Name Diode characteristics (Si, Zener, LED) Transistor characteristics (CB NPN) Transistor characteristics (CB PNP) Transistor characteristics (CE NPN) Transistor characteristics (CE PNP) Transistor characteristics (CC NPN) Transistor characteristics (CC PNP) FET characteristics Rectifier Circuits Common Emitter Amplifier Common Collector Amplifier Common Base Amplifier R-C Coupled Amplifier Cascode Amplifier Class A Amplifier Class B Amplifier (Push-Pull emitter follower) Class C tuned Amplifier Phase Locked Loop (FM Demodulator & Frequency Multiplier/Divider) Multivibrators (Astable / Monostable) F-V and V-F Converter V-I and I-V Converter Zener Voltage Regulator Transistor Series Voltage Regulator Transistor Shunt Voltage Regulator DC Ammeter DC Voltmeter Differential Amplifier (Transistorized) Scientech Technologies Pvt. Ltd. 4

5 AB-42 Operational Amplifier (Inverting / Non-inverting / Differentiator) AB-43 Operational Amplifier (Adder / Scalar) AB-44 Operational Amplifier (Integrator / Differentiator) AB-51 Active Filters (Low Pass and High Pass) AB-52 Active B and Pass Filter AB-53 Notch Filter AB-56 Fiber Optic Analog Link AB-65 Phase Shift Oscillator AB-66 Wien Bridge Oscillator AB-67 Colpitt Oscillator AB-81 Kirchoff s Laws (Kirchoff s Current Law and Kirchoff s Voltage Law) AB-82 Thevenin s and Maximum Power transfer Theorem AB-83 Reciprocity and Superposition Theorem AB-84 Tellegen s Theorem AB-90 Two port network parameter AB-91 Optical Transducer (Photovoltaic cell) AB-92 Optical Transducer (Photoconductive cell/ldr) AB-93 Optical Transducer (PhotoTransistor) and many more Scientech Technologies Pvt. Ltd. 5

6 THEORY Operational amplifier is a direct-coupled high-gain amplifier usually consisting of one or more differential amplifiers and usually followed by a level translator and an output stage. The output stage is generally a pushpull or push-pull complementary-symmetry pair. An operational amplifier is available as a single integrated circuit package. The operational amplifier is a versatile device that can be used to amplify DC as well as AC input signals and was originally designed for performing mathematical operations such as addition, subtraction, multiplication, and integration. Thus the name operational amplifier seems from its original use for these mathematical operations and is abbreviated to op-amp. With the addition of suitable external feedback components, the modem day op-amp can be used for a variety of applications, such as AC and DC signal amplification, active filters, oscillators, comparators, Schmitt trigger, regulator, integrator, differentiator. Comparator (Voltage Level Detector) : An op-amp comparator is a circuit which compares an arbitrary input signal against a fixed reference voltage. The output of the comparator circuit switches between the two saturation voltages depending on the value of arbitrary input signal w.r.t the reference voltage (if the input amplitude is less than the reference voltage, output is at one saturation level and viceversa). As shown in fig. 1 a non-inverting comparator circuit. A fixed reference voltage V ref (say 1V or 2V ) is applied to the ( ) input (shown in fig. 2a for V ref = 1V and fig. 2b V ref = 1V), and the other time varying signal voltage V in is applied to the (+) input of op-amp. When V in is less than V ref, the output voltage V out is at V sat (approx. equal to V EE ) as the voltage at ( ) input terminal is higher than that of the (+) input terminal. On the other hand, when the (+) input terminal voltage V in is greater than V ref, the (+) input terminal becomes positive w.r.t. the ( ) input and the V out bring switches to +V sat (approx. equal to +V cc ). Scientech Technologies Pvt. Ltd. 6

7 Comparator (Voltage Level Detector) Fig. 1 Input-Output Waveform Comparator Fig.2 Thus, V out changes from one saturation level to another whenever V in = V ref as shown in fig. 2 (a). In short comparator is a type of analog-to-digital converter. At any given time the V out shows whether V in is greater or less than V ref. This is the reason why it is also called a voltage level detector. In the similar way if the reference voltage is negative w.r.t. ground, with the sinusoidal input applied to the noninverting terminal of op-amp the output will be as shown in fig. 2 (b). Scientech Technologies Pvt. Ltd. 7

8 Zero-crossing Detector (Sine wave-to-square Wave Converter) : The above shown circuit can also be used as a zero crossing detector provided that V ref is set to zero (V ref = 0). As shown in fig. 3 (a), which is an inverting comparator used as a zero - crossing detector. Schmitt Trigger : Fig. 3 A Schmitt Trigger is a circuit which converts an irregular shaped waveform to a square wave or pulse. This circuit is also called as a squaring circuit. A Schmitt trigger circuit is as shown in fig. 4 Schmitt Trigger (a) Circuit diagram (b) Input-output waveform Fig. 4 Scientech Technologies Pvt. Ltd. 8

9 The input voltage V in triggers (changes the state of) output V out every time exceeds certain voltage levels called upper threshold V ut and lower threshold voltage V lt as shown in fig.5. Vout vs. Vin plot of Hysteresis voltage Fig. 5 These threshold voltages can be obtained by using the voltage divider R 1 - R 2, where the voltage across R 1 is fed back to the (+) input. The voltage across R 1 is a variable reference threshold voltage that depends on the value and the polarity of the output voltage. When V out = +V sat, the voltage across R 1 is called the upper threshold voltage, V ut. The input voltage V in must be slightly more +ve than V ut in order to cause the output voltage V out to switch from +V sat to -V sat. As long as V in < V ut, V out is at +V sat. Using the voltage divider rule, V R1 = ( Vsat ).. (1) R + R ut On the other hand, when Vo = -V sat, the voltage across R 1 is referred to as lower threshold voltage, V lt. V in must be slightly more negative than V lt in order to cause V out to switch from -V sat to +V sat. In other words, for V in values greater than V lt, V out is at -V sat. V lt is given by the following equation. V lt R1 = ( Vsat ).. (2) R + R 1 2 Scientech Technologies Pvt. Ltd. 9

10 Thus if the threshold voltages V ut and V lt are made larger than the input noise voltages, the positive feedback will eliminate the false output transitions. Also, the positive feedback, because of its regenerative action, will make V out to switch faster between +V sat and -V sat. The comparator with positive feedback is said to exhibit hysteresis, a dead zone. That is when the input of the comparator exceeds V ut, its output switches from +V sat to -V sat and revert back to its original state +V sat, when the input goes below V lt. The hysteresis voltage is, equal to the difference between V ut and V lt. Therefore, V hy = Vut Vlt R1 V hy = [ + Vsat ( Vsat )] R + R (3) Scientech Technologies Pvt. Ltd. 10

11 Object : EXPERIMENT 1 To study Operational Amplifier as a Comparator and Zero Crossing Detector. Apparatus Required : 1. Analog board of AB DC power supplies +12V, -12V and variable +5V and -5V from external source or ST-2612 Analog Lab. 3. Oscilloscope 4. Function Generator mm. patch cords. Circuit Diagram : Circuit used to study Op-amp as Comparator is as shown in Fig. 6. Scientech Technologies Pvt. Ltd. 11 Fig. 6

12 Procedure : Connect +12V and -12V DC power supplies at their indicated positions on AB-45 board from external source or ST-2612 Analog Lab. 1. Connect variable +5V DC signal between points a and g1 i.e. to the inverting input of the Op-amp through 300 Ohms resistance. This DC signal will act as a reference voltage against which the level of input signal will be compared. 2. Connect a 10Vp-p, 1KHz signal between points f and g2 i.e. to the non-inverting input of the Op-amp. (Select the inverting and noninverting input terminal resistance values to be equal). 3. Adjust the variable DC signal to 1V and observe the output waveform between points i and g3 on Ch I of oscilloscope and input signal on Ch II of oscilloscope. 4. Vary the DC signal gradually from 1V to 5V and observe the output voltage waveform with respect to input signal. 5. Disconnect the +5V variable supply and connect variable -5V DC signal between points a and g1 i.e. to the inverting input of the Op-amp through 300 Ohms resistance. This DC signal will act as a reference voltage against which the level of input signal will be compared. 6. Vary the DC signal gradually from -1V to -5V and observe the output voltage waveform with respect to input signal. 7. Plot the output waveforms on graph paper for both the above cases. (Refer fig.1 and fig.2). 8. Connect the point a to the point g1 of AB-45 board to analyze Op-amp as Zero Crossing Detector. This connection will make reference voltage to be equal to 0V (V ref = 0V). 9. Observe the output waveform between points i and g3 on Ch I of oscilloscope and input signal on Ch II. 10. To make sure that the output waveform is crossing zero level at the same instant to that of the input signal, adjust the offset pot. Scientech Technologies Pvt. Ltd. 12

13 11. Plot the output waveforms on graph paper for the V ref = 0V. (Refer fig. 3a and 3b). Scientech Technologies Pvt. Ltd. 13

14 Object : EXPERIMENT 2 To study Operational Amplifier as a Schmitt Trigger. Apparatus Required : 1. Analog board of AB DC power supplies +12V, -12V from external source or ST-2612 Analog Lab. 3. Oscilloscope. 4. Function Generator. 5. Digital Voltmeter mm. patch cords. Circuit Diagram : Circuit used to study Op-amp as Schmitt Trigger is as shown in Fig. 6. Fig. 6 Scientech Technologies Pvt. Ltd. 14

15 Procedure : Connect +12V & -12V DC power supplies at their indicated positions on AB-45 board from external source or ST-2612 Analog Lab. 1. Connect the point g and h using a 2mm patch cord. This will activate the positive feedback to the op-amp circuit. 2. Connect point d with g2 using a 2mm patch cord. 3. Connect a 10V p-p, 1 KHz sine wave signal between points a and g1 i.e. to the inverting input of the Op-amp (R 1 = R 4 R F ). You can also connect points e and g2 or points f and g2 and signal will be applied between point b and g1 or c and g1 respectively. (Refer to fig. 4a) 4. Observe the output waveform between points i and g3 on Ch I of oscilloscope and input signal on Ch II of oscilloscope. 5. Calculate the amplitude of the square wave (The square wave amplitude will vary between +Vsat = +12V and -Vsat = -12V). You can check this by applying some other value of DC signals, say +5V and -5V or + 15V and -15V, and check the amplitude. 6. You can also check the above point by varying the input signal amplitude and observing whether the output signal amplitude varies with the input signal amplitude variations or not. 7. Connect a 10V p-p, 1KHz triangular wave signal between points a and g1 i.e. to the inverting input of the Op-amp (R 1 = R 4 R F ). 8. Calculate V ut and V lt using Eq. (1) and (2) respectively for the following three cases: a. Signal applied between points a and g1 and points d and g2 are connected using a 2mm patch cord. b. Signal applied between points b and gl and points e and g2 are connected using a 2mm patch cord. c. Signal applied between points c and g1 and points f and g2 are connected using a 2mm patch cord. 9. Check the voltage drop across R 4, R 5 and R 6 respectively for the above three cases using DMM and check the results against the theoretically calculated values in step 8. Scientech Technologies Pvt. Ltd. 15

16 10. Calculate the Hysteresis voltage for the above three cases using Eq.3 and plot the Hysteresis voltage on graph paper (Refer to fig. 5). Scientech Technologies Pvt. Ltd. 16

17 DATASHEET Scientech Technologies Pvt. Ltd. 17

18 WARRANTY 1) We guarantee the instrument against all manufacturing defects during 24 months from the date of sale by us or through our dealers. 2) The guarantee covers manufacturing defects in respect of indigenous components and material limited to the warranty extended to us by the original manufacturer, and defect will be rectified as far as lies within our control. 3) The guarantee will become INVALID. a) If the instrument is not operated as per instruction given in the instruction manual. b) If the agreed payment terms and other conditions of sale are not followed. c) If the customer resells the instrument to another party. d) Provided no attempt have been made to service and modify the instrument. 4) The non-working of the instrument is to be communicated to us immediately giving full details of the complaints and defects noticed specifically mentioning the type and sr. no. of the instrument, date of purchase etc. 5) The repair work will be carried out, provided the instrument is dispatched securely packed and insured with the railways. To and fro charges will be to the account of the customer. DESPATCH PROCEDURE FOR SERVICE Should it become necessary to send back the instrument to factory please observe the following procedure: 1) Before dispatching the instrument please write to us giving full details of the fault noticed. 2) After receipt of your letter our repairs dept. will advise you whether it is necessary to send the instrument back to us for repairs or the adjustment is possible in your premises. Dispatch the instrument (only on the receipt of our advice) securely packed in original packing duly insured and freight paid along with accessories and a copy of the details noticed to us at our factory address. Scientech Technologies Pvt. Ltd. 18

19 LIST OF SERVICE CENTERS 1. Scientech Technologies P. Ltd. 90, Electronic Complex Ph: (0731) Pardesipura, INDORE Scientech Technologies P. Ltd. First Floor, Ph.: (011) , , Uday Park, Fax: (011) NEW DELHI Scientech Technologies P. Ltd. New no.2, Old no.10, 4 th street Ph.: (044) , Venkateswara nagar, Adyar Fax: (044) CHENNAI chennai@scientech.bz 4. Scientech Technologies P. Ltd. 202/19, 4 th main street Ph.: (080) Ganganagar, Fax: (080) BANGALORE bangalore@scientech.bz 5. Scientech Technologies P. Ltd. 8,1st floor, 123-Hariram Mansion, Ph.: (022) Dada Saheb Phalke Road Fax: (022) Dadar (East) stplmum@vsnl.net MUMBAI Scientech Technologies P. Ltd. 988, Sadashiv Peth, Ph.: (020) Gyan Prabodhini Lane, Fax: (020) PUNE pune@scientech.bz 7. Scientech Technologies P. Ltd SPS Apartment, 1 st Floor Ph , Ahmed Maooji Street, E mail: kolkata@scientech.bz Behind Jaiswal Hospital, Liluah, Howrah W.B. LIST OF ACCESSORIES 1. 2mm Patch cord (red)...2 Nos. 2. 2mm Patch cord (black)...3 Nos. 3. 2mm Patch cord (blue)...4 Nos. Scientech Technologies Pvt. Ltd. 19