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AB-67

AB-67

COLPITT OSCILLATOR

ANALOG LAB EXPERIMENTAL BOARD

Operation & ExperimentManual

SCIENTECH TECHNOLOGIES PVT. LTD. 1

AB-67

CONTENTS

Page No.

• Introduction 3

• Theory 5

• Experiment 7To study the operation of Colpitt Oscillator.

Data sheet 9

• Notes 11

SCIENTECH TECHNOLOGIES PVT. LTD.2

AB-67

IntroductionAB-67 is a compact, ready to use Colpitt Oscillator experiment board. This is useful for students to understand functionality of Colpitt oscillator. 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:

AB-01 Diode characteristics (Si, Zener, LED)AB-02 Transistor characteristics (CB NPN)AB-03 Transistor characteristics (CB PNP)AB-04 Transistor characteristics (CE NPN)AB-05 Transistor characteristics (CE PNP)AB-06 Transistor characteristics (CC NPN)AB-07 Transistor characteristics (CC PNP)AB-08 FET characteristicsAB-15 Common Emitter AmplifierAB-16 Common Collector AmplifierAB-17 Common Base AmplifierAB-21 Class A AmplifierAB-22 Class B push pull emitter follower AmplifierAB-23 Class C RF tuned AmplifierAB-26 VCO (Frequency Modulator) using IC LM565AB-27 Phase Locked LoopAB-28 Multivibrators (Astable/Monostable)AB-29 F-V and V-F ConverterAB-30 V-I and I-V ConverterAB-31 Zener Voltage Regulator AB-32 Transistor Series Voltage Regulator AB-33 Transistor Shunt Voltage Regulator AB-41 Differential Amplifier (Transistorized)


AB-67AB-42 Operational Amplifier (Inverting/Non inverting/Differential)AB-43 Operational Amplifier (Adder/Scalar)AB-44 Operational Amplifier (Integretor/Differentiator)AB-45 Schmitt Trigger and ComparatorAB-51 Active filters (Low Pass and High Pass)AB-52 Active Band Pass Filter AB-53 Notch Filter (active + passive)AB-56 Fiber Optic Analog LinkAB-65 Phase Shift OscillatorAB-66 Wien Bridge OscillatorAB-67 Colpitt OscillatorAB-71 UJT characteristics AB-72 MOSFET characteristics AB-73 SCR characteristics AB-74 TRIAC characteristics AB-75 DIAC characteristics AB-81 Kirchoff’s LawsAB-82 Thevenin’s and Maximum power transfer TheoremAB-83 Reciprocity and Superposition TheoremAB-84 Tellegen’s TheoremAB-90 Two port network parameterAB-91 Optical Transducer (Photovoltaic cell)AB-92 Optical Transducer (Photoconductive cell/LDR)AB-93 Optical Transducer (PhotoTransistor)


AB-67Theory

Oscillators are circuits that produce specific, periodic waveforms such as square, triangular, sawtooth, and sinusoidal. They can be made from some form of active or passive device like transistor, FETs and op-amp in association with devices such as resistors, capacitors, and inductors, to generate the output.

There are two main classes of oscillator: relaxation and sinusoidal. Relaxation oscillators generate the triangular, sawtooth and other nonsinuoidal waveforms. Sinusoidal oscillators consist of amplifiers with external components used to generate oscillation, or crystals that internally generate the oscillation. The focus here is on sine wave oscillators. Sine wave oscillators are used as references or test waveforms by many circuits.

An oscillator is a type of feedback amplifier in which part of the output is fed back to the input via a feedback circuit. If the signal fed back is of proper magnitude and phase, the circuit produces alternating currents or voltages. Two requirements for oscillation are 1.The magnitude of the loop gain AvB must be at least 1, and2.The total phase shift of the loop gain AvB must be equal to 0o or 360o.If the amplifier causes a phase shift of 180o, the feedback circuit must provide an additional phase shift of 180o so that the total phase shift around the loop is 360o.

Colpitt OscillatorThe Colpitt oscillator is one of the simplest and best known oscillators and is used extensively in circuits, which work at radio frequencies. Fig.1 shows the basic Colpitt oscillator circuit configuration. The transistor is in voltage divider bias which sets up Q-point of the circuit.In the circuit note that Vout is actually the ac voltage across C2. This voltage is fed back to the base and sustains oscillations developed across the tank circuit, provided there is enough voltage gain at the oscillation frequency.


AB-67

The resonant frequency of the Colpitt oscillator can be calculated from the tank circuit used. We can calculate the approx. resonant frequency as Resonant Frequency (Fr) = ……………(1) Here, the capacitance used is the equivalent capacitance the circulating current passes through. In Colpitt oscillator the circulating current passes through the series combination of C1 and C2. therefore equivalent capacitance is,

Cequ =


12π√ (LC )

C1 * C2 C1 + C2

AB-67Experiment

Object: To study the operation of Colpitt Oscillator.

Apparatus required: 1.Analog board AB-67.2.DC power supplies +12V from external source or ST-2612 Analog Lab.3.Oscilloscope. 4.2mm Patch cords.

Circuit diagram: Circuit used to study the operation of Colpitt Oscillator is as shown in Fig.2.

Fig 2


AB-67Procedure: • To study Colpitt oscillator proceed as follows :-

1. Connect +12V dc power supplies at their indicated position from external source or ST-2612 Analog Lab.2. Connect a patch cord between points a and b and another patch chord between points d and g1.3. Switch ON the power supply.4. Connect oscilloscope between points f and g2 on AB–67 board.

5. Record the value of output frequency on oscilloscope.6. Calculate the resonant frequency using equation 1.7. Compare measured frequency with the theoretically calculated

value.8. Switch off the supply.9. Remove the patch chord connected between points a and b and

connect it between points a and c.10. Remove the patch chord connected between points d and g1 and

connect it between points e and g2.11. Follow the procedure from point 4 to 8.12. Connect +5V supply instead of +12V supply and follow the

procedure from point 2 to point 11.

Result:When patch chord connected across C1 and C2Practically calculated Output frequency(on CRO): …………………….Theoretically calculated valuesCequ : ……………………………………... ( use eq.2 )Resonant frequency (fr) : ………………….. ( use eq.1 )Output voltage amplitude : …………………… Vp-pWhen patch chord connected across C3 and C4Practically calculated Output frequency(on CRO): …………………….Theoretically calculated valuesCequ : ……………………………………... ( use eq.2 )Resonant frequency (fr) : ………………….. ( use eq.1 )Output voltage amplitude : …………………… Vp-p


AB-67Record above results separately for +12V input voltage and +5V input voltage and note down the .

DatasheetDatasheet


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AB-67

NOTES:


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Operation & Experiment Manual · Operation & Experiment Manual ... AB-30 V-I and I-V Converter AB-31 Zener Voltage Regulator ... AB-73 SCR characteristics