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AB18 RC-COUPLED AMPLIFIER Analog Lab Experiment Board Ver. 1.0 QUALITY POLICY To be a Global Provider of Innovative and Affordable Electronic Equipments for Technology Training by enhancing Customer Satisfaction based on Research, Modern manufacturing techniques and continuous improvement in Quality of the products and Services with active participation of employees. An ISO 9001: 2000 company 94-101, Electronic Complex, Pardesipura INDORE-452010, India. Tel.: 91-731-2570301 Fax: 91-731-2555643 AB18 Email: [email protected] Web: www.scientech.bz Scientech Technologies Pvt. Ltd. 2 AB18 Scientech Technologies Pvt. Ltd. 3 AB18 RC-COUPLED AMPLIFIER AB18 TABLE OF CONTENTS 1. Introduction 4 2. Theory 6 3. Experiments a. Experiment 1 10 To study the operation of RC – coupled Amplifier b. Experiment 2 12 To study the frequency response of RC – coupled Amplifier. Datasheet 14 4. Warranty 16 5. List of service Centers 17 6. List of Accessories with AB18 18 7. Notes 19 Scientech Technologies Pvt. Ltd. 4 AB18 INTRODUCTION AB18 is a compact, ready to use RC – COUPLED AMPLIFIER experiment board. This board is useful for students to understand the working and operation of coupling used to cascade various amplifier stages. 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 AB01 AB02 AB03 AB04 AB05 AB06 AB07 AB08 AB09 AB10 AB15 AB16 AB17 AB19 AB21 AB22 AB23 AB25 AB28 AB29 AB30 AB31 AB32 AB33 AB40 AB41 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 Wheatstone Bridge Common Emitter Amplifier Common Collector Amplifier Common Base Amplifier Cascode Amplifier Class A Amplifier Class B Amplifier (push pull emitter follower) Class C Tuned Amplifier Phase Locked Loop (FM Demodulator & Frequency Multiplier) 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 Op-amp Characteristics Differential Amplifier (Transistorized) Scientech Technologies Pvt. Ltd. 5 AB18 AB42 AB43 AB44 AB45 AB51 AB52 AB53 AB56 AB65 AB66 AB67 AB81 AB82 AB83 AB84 AB90 AB91 AB92 AB93 Operational Amplifier (Inverting / Noninverting / Differentiator) Operational Amplifier (Adder/Scalar) Operational Amplifier (Integrator/ Differentiator) Schmitt Trigger and Comparator Active filters (Low Pass and High Pass) Active Band Pass Filter Notch Filter Fiber Optic Analog Link Phase Shift Oscillator Wien Bridge Oscillators Colpitt Oscillator Kirchoff’s Laws (Kirchoff’s Current Law & Kirchoff’s Voltage Law) Thevenin’s and Maximum power Transfer Theorem Reciprocity and Superposition Theorem Tellegen’s Theorem Two port network parameter Optical Transducer (Photovoltaic cell) Optical Transducer (Photoconductive cell/LDR) Optical Transducer (PhotoTransistor) …. and many more Scientech Technologies Pvt. Ltd. 6 AB18 THEORY Single amplifier circuits, such as a common emitter, common base and common collector amplifiers are seldom found alone, as a single stage amplifier, in any system. Generally, at least two or more than two stages are connected in cascade combination. If the output of one amplifier is connected (coupled) to the input of another amplifier the stages are said to be connected in "cascade". The benefit of cascaded amplifiers is to develop an output voltage larger than either stage alone can develop. In fact, the overall gain of the cascaded amplifiers (called system gain) is the product of each individual stage gain, or AV = AVl X AV2 X AVn ………….(1) Total Voltage = gain of X gain of X gain of any Gain first stage second stage number of stages Fig. 1 Because of this the gain of a single stage is not as important as the system gain. Designers usually set individual stage gains relatively low to reduce signal distortion. One of the very important requirements to cascade one stage of amplifier to another is the impedance matching. When the output impedance of pervious stage matches with the input impedance of its next stage, maximum power is transferred. One of the coupling methods to couple the two stages is RC-coupling. RC Coupling has the advantages of wide frequency response and relatively small cost and size. Scientech Technologies Pvt. Ltd. 7 AB18 RC Coupled Amplifier Stages Fig. 2 An RC-Coupled network is shown in fig.2. The network of R2 and Cl enclosed in the dashed lines is the coupling network. C1 is the coupling capacitor which connects the output of Ql to the input of Q2. R2 will develop the signal to be applied to the base of Q2. Cl acts as a limiting Figure 3a Scientech Technologies Pvt. Ltd. Fig. 3 Figure 3b 8 AB18 factor at low frequencies because its reactance increases with a decrease in frequency and some point will be reached when a voltage drop will appear across it. This will reduce the size of the signal being applied to Q2. At medium frequencies the reactance of Cl is so small that it can be considered a short to the signal. C1 will also isolate any DC voltage developed at the collector of Q1 from the DC bias developed at the base of Q2. Consider fig.3a, assume that Ql and Q2 are in a static slate, (no signal applied). Let current flow through Ql develops 6VDC at the collector (Vc) and current flow through the base biasing network of Q2 (R21 and R22) develops 2VDC at the base of Q2 (Vb). Cc charges through R22 to the difference in the potentials on either side of it and will assume a charge of 4VDC (6V-2V = 4V). When a signal is applied to the base of Ql, the current changes through the collector resistor (Rcl) will cause the Ql collector voltage to vary. In this instance assume the collector rises to 7V. See figure 3b. As collector voltage rises, the tendency of Cc is to charge to the higher potential. However, a capacitor cannot change its charge instantly. As Cc starts to change its charge, charge current will be felt through R22. Cc will now start to change to lV. As Cc increases its charge, additional current will be drawn through R22 causing R22 to increase its voltage drop. The voltage at Q2's base, which is the voltage drop across R22, will now rise from 2V to 3V. As the collector voltage at Ql starts to decrease. Cc will attempt to discharge. Electrons being forced off the right plate of Cc, as it attempts to discharge, will now flow through R21 increasing its voltage drop which results in a decrease in the voltage drop across R22. As Ql's collector voltage decrease further it will result in Cc decreasing its charge further. As Ql collector voltage drops to 5V, Cc will continue to attempt to discharge. As Cc continues to discharge, the voltage drop of R22 decreases to 1V. As Q1 collector voltage starts to go positive, Cc will start to increase its charge. This causes the current through R22 to increase which results in the voltage drop across R22 increasing. When the collector voltage of Q1 returns to its original 6V the voltage at Q2's base will have returned to 2V. Notice that the signal developed at the collector of Ql has caused Cc to vary its charge resulting in varying current level through R22 and R21. The signal developed by these currents resulted in a signal being developed at the base of Q2 which is identical to Ql's collector signal. Although the signals on both sides of the capacitor are identical, the base signal of Q2 did Scientech Technologies Pvt. Ltd. 9 AB18 not pass through Cc, it just appears to. Normally we would say "the signal developed by Ql will be coupled by Cc to Q2's base". Bandwidth of an RC - Coupled Amplifier : Bandwidth is a term used to describe the band of frequencies a particular amplifier will effectively amplify. Fig. 4 The f1 and f2 points are also known as half power points. The half power points are the points at which the signal amplitude has dropped to .707 percent of the maximum signal amplitude. Any frequency below the f1 or above the f2 point is not considered a usable output from the amplifier. The bandwidth of the amplifier is the difference between the f1 and f2 points. It is generally accepted that in an RC -Coupled amplifier the fl point is established by the coupling capacitor and by-pass capacitor and the f2 point is set by the "shunt" or "stray wire" capacitance. The bandwidth of RC-Coupled Amplifier is given by, Bandwidth (B) = f2 – f1 Scientech Technologies Pvt. Ltd. …………….(2) 10 AB18 EXPERIMENT 1 Object : To study the operation of RC – Coupled amplifier. Apparatus required : 1. 2. Analog board AB18. 3. Function Generator. 4. Oscilloscope. 5. 2mm patch chords. DC power supply +12V from external source or ST-2612 Analog Lab. Circuit diagram : Circuit used to study the operation of RC-Coupled amplifier is shown below : Scientech Technologies Pvt. Ltd. 11 AB18 Fig. 5 Scientech Technologies Pvt. Ltd. 12 AB18 Procedure : • Connect +12V variable dc power supplies at their indicated position from external source or ST2612 Analog Lab. 1. Connect 2Vp-p, 1 KHz Sine wave signal at the input (between points Vin and g1) of amplifier named Stage1 of AB18 board and observe the same on oscilloscope CH I. 2. Connect point b and c using a 2mm patch cord (this will connect a load RL at the output of Stage1. 3. Observe the output waveform of Stage 1 between points a and g2.on oscilloscope CH II. 4. 5. Calculate the Voltage Gain (AV1). 6. Observe the output waveform of Stage 2 between points Vout and g4 on oscilloscope CH II. 7. 8. 9. Calculate the Voltage Gain (AV2). 10. Connect 2Vp-p, 1 KHz Sine wave signal at the input (between points Vin and g1) of amplifier named Stage1 of AB18 board and observe the same on oscilloscope CH I. 11. Observe the output waveform at Stage 2 between points Vout and g4 on oscilloscope CH II. Apply the same signal (i.e. 2Vp-p, 1KHz Sine wave signal) to the input of Stage2 (between points d and g3) of AB18 board and observe the same on oscilloscope CH I. Calculate Total Voltage Gain (Av) using Eq. (1). Remove the pervious connections and connect point b with point d of AB18 board. This will cascade the two stages through R C coupling. Where Cc is the coupling capacitor and the combination of R21 and R22 will act as coupling resistance. 12. Calculate the Voltage Gain (AV’). 13. Compare the two results obtained from step no.8 and 12. Result : Voltage Gain of Stage 1 [AV1 = Vout1/ Vin1] = …………………….. Voltage Gain of Stage 2 [ AV2 = Vout2/Vin2 ] = …………………… Av (from eq.1) =…………………….. Scientech Technologies Pvt. Ltd. 13 AB18 Av’ = …………………. EXPERIMENT 2 Object : To study the Frequency Response of RC – Coupled amplifier. Apparatus required : 1. 2. Analog board AB18. 3. Function Generator. 4. Oscilloscope. 5. 2mm patch chords. DC power supply +12V from external source or ST2612 Analog Lab. Circuit diagram : Circuit used to study the Frequency Response of RC-Coupled amplifier is shown below: Scientech Technologies Pvt. Ltd. 14 AB18 Fig. 5 Procedure : • Connect +12V variable dc power supplies at their indicated position from external source or ST-2612 Analog Lab. 1. Connect point b with d of AB18 board. This will cascade the two stages through RC coupling. Where Cc is the coupling capacitor and the combination of R21 and R22 will act as coupling resistance. 2. Connect 1Vp-p, 100Hz Sine wave signal at the input (between points Vin and g1) of amplifier named Stage1 of AB18 board and observe the same on oscilloscope CH I. 3. Observe the output waveform at Stage 2 between points Vout and g4 on oscilloscope CH II. 4. Increase the amplitude of input signal to the value before the output sine wave just gets distorted. 5. Increase the input frequency value and observe the output waveform amplitude on oscilloscope. 6. Measure the maximum amplitude of the output sine wave and the frequency range for which the output wave amplitude is 3dB down the maximum amplitude.(this will give two valves of frequency fL and fH, the lower 3dB frequency and higher 3dB frequency respectively) as shown in fig.5. 7. Calculate Bandwidth of RC-Coupled amplifier using Eq.2 Result : f1 (lower 3dB frequency) = ………………………. f2 (higher 3dB frequency) = ………………………. Bandwidth (f2 – f1) = ……………………. Scientech Technologies Pvt. Ltd. 15 AB18 DATASHEET Scientech Technologies Pvt. Ltd. 16 AB18 Scientech Technologies Pvt. Ltd. 17 AB18 Scientech Technologies Pvt. Ltd. 18 AB18 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. 19 AB18 LIST OF SERVICE CENTERS 1. Scientech Technologies Pvt. Ltd. 90, Electronic Complex Pardesipura, INDORE – 452010 2. Scientech Technologies Pvt. Ltd. First Floor, 14, Uday Park, NEW DELHI – 110049 3. Scientech Technologies Pvt. Ltd. New no.2, Old no.10, 4th street Venkateswara nagar, Adyar CHENNAI – 600025 4. Scientech Technologies Pvt. Ltd. 202/19, 4th main street Ganganagar, BANGALORE- 560032 5. Scientech Technologies Pvt. Ltd. 8,1st floor, 123-Hariram Mansion, Dada Saheb Phalke road, Dadar (East), MUMBAI –400014 6. Scientech Technologies Pvt. Ltd. 988, Sadashiv Peth, Gyan Prabodhini Lane, PUNE – 411030 7. Scientech Technologies Pvt. Ltd SPS Apartment, 1st Floor 2, Ahmed Mamoji Street, Behind Jaiswal Hospital, Liluah, HOWRAH-711204 W.B. 8. Scientech Technologies Pvt. Ltd Flat No. 205, 2nd Floor, Lakshminarayana Apartments ‘C’ wing, Street No. 17, Himaytnagar, HYDERABAD- 500029 Scientech Technologies Pvt. Ltd. Ph: (0731) 5202959 Email: [email protected] Ph.: (011) 26513912, 26864943 Fax: (011) 26864943. Email: [email protected] Ph.: (044) 42187548, 42187549 Fax: (044) 42187549 Email: [email protected] Ph.: (080) 51285011 Fax: (080) 51285022 Email: [email protected] Ph.: (022) 56299457 Fax: (022) 24168767 Email: [email protected] Ph.: (020) 24461673 Fax: (020) 24482403 Email: [email protected] Ph.: +913355266800 Email: [email protected] Ph.: (040) 55465643 Email: [email protected] 20 AB18 LIST OF ACCESSORIES 1. 2mm patch cord (red)..............................................................1 No. 2. 2mm patch cord (blue)...........................................................4 Nos. 3. 2mm patch cord (black).........................................................4 Nos. Scientech Technologies Pvt. Ltd. 21 AB18 NOTES Scientech Technologies Pvt. Ltd. 22 AB18 NOTES Scientech Technologies Pvt. Ltd. 23