Tuned Collector, Hartley and Colpitts Oscillators for SS 3

Class: SS 3
Term: First Term
Week: 6
Age: 14 years
Duration: 45 minutes
Subject: Basic Electronics
Previous Lesson: Oscillators and Feedback Principles
Topic: OSCILLATOR
Subject Matter: Types of oscillator e.g. tuned collector, Hartley oscillator and colpit oscillator etc

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Define an oscillator.
• Identify the key components of a Tuned Collector oscillator.
• Explain the working principle of a Hartley oscillator.
• Differentiate between Hartley and Colpitts oscillators based on their tank circuits.
• State one application for each type of oscillator discussed.

Affective Domain

• Appreciate the importance of oscillators in electronic circuits.
• Show interest in learning more about different oscillator designs.

Psychomotor Domain

• Sketch simple diagrams of the Tuned Collector, Hartley, and Colpitts oscillators.
• Identify the feedback network in each oscillator type.

Social Domain

• Collaborate with peers to discuss the characteristics of different oscillators.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Basic Electronics textbooks for Senior Secondary School 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Whiteboard and markers
• Prepared charts or diagrams of Tuned Collector, Hartley, and Colpitts oscillators
• Textbooks on Basic Electronics

Rationale for the Lesson

This lesson is important because oscillators are fundamental building blocks in almost all electronic communication systems, from radio transmitters to clock generators in computers. Understanding different types of oscillators helps students grasp how alternating current signals are generated and prepares them for advanced topics in electronics and communication engineering.

Prerequisite/Previous Knowledge

Students should have a basic understanding of transistors (BJTs), capacitors, inductors, resistors, and the concept of positive feedback in electronic circuits.

Lesson Content/Board Summary

OSCILLATOR

Types of Oscillators

An oscillator is an electronic circuit that produces a repetitive, oscillating electronic signal, often a sine wave or a square wave, without any input signal. Oscillators convert DC power from a power supply into an AC signal.

Tuned Collector Oscillator

The Tuned Collector oscillator uses a parallel LC (inductor-capacitor) tank circuit in the collector of a transistor to determine the oscillation frequency. Feedback is provided from the collector to the base via a mutual inductance between the collector coil and a feedback coil in the base circuit.

1. The tank circuit (L and C) in the collector determines the resonant frequency.
2. Positive feedback is achieved through inductive coupling from the collector tank circuit to the base.
3. The transistor amplifies the signal, making up for losses in the tank circuit.

Hartley Oscillator

The Hartley oscillator is an LC oscillator that uses a tapped inductor (or two inductors in series) in parallel with a capacitor to form its tank circuit. The feedback signal is taken from the junction of the two inductors and applied to the base of the transistor.

1. The tank circuit consists of two inductors (L1, L2) in series and a capacitor (C) in parallel.
2. The feedback is derived from the voltage across one of the inductors (L2) and applied to the base.
3. It is suitable for generating high-frequency oscillations.

Colpitts Oscillator

The Colpitts oscillator is another LC oscillator that uses a tapped capacitor (or two capacitors in series) in parallel with an inductor to form its tank circuit. The feedback signal is taken from the junction of the two capacitors and applied to the base of the transistor.

1. The tank circuit consists of two capacitors (C1, C2) in series and an inductor (L) in parallel.
2. The feedback is derived from the voltage across one of the capacitors (C2) and applied to the base.
3. It provides good frequency stability and is often used in radio frequency (RF) applications.

Teaching Methods/Instructional Techniques

Discussion, Explanation, Demonstration, Question and Answer, Guided Practice

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Eliciting prior knowledge

Teacher’s Activity: The teacher begins by asking students what an oscillator is and where they might have encountered oscillating signals in electronics. The teacher then introduces the topic of different types of oscillators.

Pupils’ Activity: Pupils respond to questions and listen attentively to the introduction.

Learning Point: Oscillator concept review

Step 2: Tuned Collector Oscillator

Time: 8 minutes

Teaching Skill: Explanation/Diagramming

Teacher’s Activity: The teacher explains the Tuned Collector oscillator, drawing its circuit diagram on the board or displaying a prepared chart. The teacher highlights the tank circuit in the collector and the inductive feedback mechanism.

Pupils’ Activity: Pupils observe the diagram, listen to the explanation, and ask questions for clarity.

Learning Point: Tuned Collector characteristics

Step 3: Hartley Oscillator

Time: 8 minutes

Teaching Skill: Explanation/Comparison

Teacher’s Activity: The teacher proceeds to explain the Hartley oscillator, drawing its circuit diagram and pointing out the tapped inductor in the tank circuit. The teacher compares its feedback mechanism with the Tuned Collector type.

Pupils’ Activity: Pupils observe the diagram, follow the explanation, and note the distinguishing features of the Hartley oscillator.

Learning Point: Hartley oscillator features

Step 4: Colpitts Oscillator

Time: 8 minutes

Teaching Skill: Explanation/Differentiation

Teacher’s Activity: The teacher introduces the Colpitts oscillator, drawing its circuit diagram and emphasizing the tapped capacitors in its tank circuit. The teacher guides students to differentiate it from the Hartley oscillator.

Pupils’ Activity: Pupils observe the diagram, understand the explanation, and identify the unique aspects of the Colpitts oscillator.

Learning Point: Colpitts oscillator features

Step 5: Comparison and Applications

Time: 5 minutes

Teaching Skill: Summarisation/Application

Teacher’s Activity: The teacher briefly summarises the key differences between the three types of oscillators discussed, focusing on their tank circuits and feedback. The teacher also mentions common applications for each.

Pupils’ Activity: Pupils participate in the summary and identify the differences and applications.

Learning Point: Oscillator type comparison

Step 6: Reinforcement

Time: 2 minutes

Teaching Skill: Questioning

Teacher’s Activity: The teacher asks quick questions to ensure students grasp the main concepts of each oscillator type.

Pupils’ Activity: Pupils answer the questions, reinforcing their understanding.

Learning Point: Oscillator principles reinforced

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is the primary function of an oscillator?
2. How does a Tuned Collector oscillator obtain feedback?
3. What is the main difference in the tank circuit between a Hartley and a Colpitts oscillator?
4. Sketch a simple diagram of a Hartley oscillator.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Oscillator types identified

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on the types of oscillators into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Oscillator notes copied

Step 9: Conclusion

Time: 0 minutes

Teaching Skill: Summarisation

Teacher’s Activity: The teacher briefly reiterates that oscillators are crucial for generating repetitive signals and that the Tuned Collector, Hartley, and Colpitts are common examples, each with distinct tank circuits and feedback mechanisms.

Pupils’ Activity: Pupils listen to the concluding remarks.

Learning Point: Main oscillator types

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook:

1. Describe the main components of a Tuned Collector oscillator.
2. Explain how positive feedback is achieved in a Colpitts oscillator.
3. Draw and label the circuit diagram of a Hartley oscillator.
4. Research and write down one practical application for each of the three oscillator types discussed today.

Lesson Keywords

• Oscillator – An electronic circuit that produces a repetitive, oscillating electronic signal without an input signal.
• Tuned Collector Oscillator – An oscillator using an LC tank circuit in the collector and inductive feedback.
• Hartley Oscillator – An LC oscillator characterized by a tapped inductor in its tank circuit.
• Colpitts Oscillator – An LC oscillator characterized by a tapped capacitor in its tank circuit.
• Tank Circuit – A parallel LC circuit that determines the resonant frequency of an oscillator.
• Feedback – The process of returning a portion of the output signal to the input.

Differentiation

For weaker learners, the teacher can provide simplified diagrams with key components clearly labelled and focus on identifying the tank circuit and feedback path for each oscillator. Faster learners can be challenged to research the Barkhausen criterion for oscillation and apply it to one of the discussed oscillator types, or investigate other types of oscillators like RC phase-shift oscillators.

Suggested Lesson Videos

For further understanding, students can search YouTube for: tuned collector hartley colpitts oscillators SS3

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have clear, large diagrams of the Tuned Collector, Hartley, and Colpitts oscillators ready to display or draw. A good understanding of how the tank circuit and feedback mechanism work for each type is essential for effective explanation. Begin by reviewing the basic concept of an oscillator and positive feedback. When explaining each oscillator type, clearly point out the components forming the tank circuit (LC components) and how feedback is achieved. Encourage students to ask questions and clarify any misconceptions immediately. During Step 8 (Note-Taking), ensure students copy the Board Summary accurately. For weaker learners, provide extra guidance in identifying the key parts of the diagrams. For faster learners, encourage them to think about the advantages and disadvantages of each oscillator type. Conclude the lesson by summarising the main points and assigning the homework.