Oscillators and Feedback Principles for SS 3

Class: SS 3
Term: First Term
Week: 5
Age: 16 years
Duration: 45 minutes
Subject: Basic Electronics
Previous Lesson: Feedback Principles and Types of Feedback Amplifiers
Topic: OSCILLATOR
Subject Matter: Concept of oscillator and feedback

Specific Objectives

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

Cognitive Domain

• Define an oscillator.
• Explain the principle by which an oscillator generates continuous signals.
• Describe the role of feedback in oscillator circuits.
• Differentiate between positive and negative feedback.

Affective Domain

• Appreciate the importance of feedback in maintaining stable oscillations.
• Develop interest in the design and application of oscillator circuits.

Psychomotor Domain

• Draw a simple block diagram illustrating the feedback principle in an oscillator.

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 for Senior Secondary Schools, Book 3
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Chart of an oscillator circuit diagram
• Whiteboard and markers
• Textbooks on Basic Electronics

Rationale for the Lesson

This lesson is important as oscillators are fundamental building blocks in almost all electronic communication and timing systems. Understanding their concept and the role of feedback is essential for students to grasp how various electronic devices generate signals and maintain stability, forming a basis for advanced electronics studies.

Prerequisite/Previous Knowledge

Students should have basic knowledge of electronic components like resistors, capacitors, and transistors, as well as an understanding of amplification and AC/DC signals.

Lesson Content/Board Summary

OSCILLATOR

Concept of an Oscillator

An oscillator is an electronic circuit that produces a repetitive, oscillating electronic signal, typically a sine wave or a square wave, without an external input signal. It converts direct current (DC) from a power supply into an alternating current (AC) signal of a desired frequency.

Oscillators are essential in many electronic devices, including radios, televisions, computers, and medical equipment, where they provide timing signals or generate carrier waves for communication.

Principle of Oscillation

The fundamental principle of oscillation involves an amplifier and a frequency-selective feedback network. For an oscillator to sustain oscillations, two conditions, known as the Barkhausen criteria, must be met:

1. The loop gain (the product of the amplifier gain and the feedback network gain) must be equal to or slightly greater than unity (1).
2. The total phase shift around the loop (amplifier phase shift plus feedback network phase shift) must be 0 degrees or an integer multiple of 360 degrees.

A small noise signal or transient is amplified and fed back in phase, causing the signal to grow until limited by the circuit’s non-linearities, resulting in a stable output waveform.

Feedback in Oscillators

Feedback is the process of returning a portion of the output signal of an electronic circuit back to its input. In oscillators, feedback plays a critical role in initiating and sustaining oscillations.

Types of Feedback

1. Positive Feedback (Regenerative Feedback): This occurs when the feedback signal is in phase with the input signal, thereby reinforcing it. Positive feedback is essential for oscillators because it causes the signal to grow and sustain itself.
2. Negative Feedback (Degenerative Feedback): This occurs when the feedback signal is out of phase with the input signal, thereby reducing it. Negative feedback is generally used in amplifiers to improve stability, reduce distortion, and control gain, but it prevents oscillation.

For an oscillator to work, it must employ positive feedback to ensure that the amplified signal is continuously fed back to the input in a way that supports the generation of a continuous output waveform.

Teaching Methods/Instructional Techniques

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

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Engaging/Recalling

Teacher’s Activity: The teacher greets the students and asks them what they understand by “oscillation” in everyday terms (e.g., a swinging pendulum). The teacher then introduces the topic of oscillators in electronics.

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

Learning Point: Introduction to oscillation concept

Step 2: Explanation of Oscillator Concept

Time: 8 minutes

Teaching Skill: Explaining/Defining

Teacher’s Activity: The teacher defines an oscillator as an electronic circuit that generates repetitive AC signals from a DC power source without an external input. The teacher uses the chart of an oscillator to show a basic circuit.

Pupils’ Activity: Pupils listen, observe the chart, and ask questions for clarification.

Learning Point: Definition of an oscillator

Step 3: Explanation of Oscillation Principle

Time: 10 minutes

Teaching Skill: Explaining/Illustrating

Teacher’s Activity: The teacher explains the principle of how an oscillator works, focusing on the need for amplification and a frequency-selective network. The teacher introduces the Barkhausen criteria (loop gain and phase shift) in simple terms.

Pupils’ Activity: Pupils listen, take notes, and try to grasp the conditions for sustained oscillation.

Learning Point: Principle of oscillation

Step 4: Introduction to Feedback

Time: 5 minutes

Teaching Skill: Defining/Concept Introduction

Teacher’s Activity: The teacher introduces the concept of feedback in general terms, explaining it as returning a portion of the output to the input. The teacher then explains its significance in electronic circuits.

Pupils’ Activity: Pupils listen and contribute ideas about what feedback means.

Learning Point: Concept of feedback

Step 5: Explanation of Positive Feedback

Time: 7 minutes

Teaching Skill: Detailing/Comparing

Teacher’s Activity: The teacher explains positive feedback as the type of feedback crucial for oscillators, where the output signal is returned in phase to reinforce the input. The teacher also briefly contrasts it with negative feedback.

Pupils’ Activity: Pupils listen, compare positive and negative feedback, and understand why positive feedback is needed for oscillators.

Learning Point: Role of positive feedback

Step 6: Discussion on Oscillator Components

Time: 3 minutes

Teaching Skill: Facilitating/Reinforcing

Teacher’s Activity: The teacher guides a brief discussion on the essential components of an oscillator (amplifier, feedback network) and how they work together to achieve oscillation.

Pupils’ Activity: Pupils identify and discuss the roles of key components in an oscillator circuit.

Learning Point: Oscillator circuit components

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 an oscillator?
2. State the two main conditions for an oscillator to work.
3. Explain the role of positive feedback in an oscillator.
4. Briefly differentiate between positive and negative feedback.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding oscillator principles

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 concept of oscillators and feedback into their notebooks.

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

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 3 minutes

Teaching Skill: Summarizing/Consolidating

Teacher’s Activity: The teacher briefly summarizes the key points of the lesson, reiterating that oscillators convert DC to AC and rely on positive feedback to generate continuous signals. The teacher encourages students to review their notes.

Pupils’ Activity: Pupils listen and ask any final questions.

Learning Point: Consolidation of oscillator concepts

Continuous Assessment/Further Study

Type: Homework

Instruction: Answer the following questions in your notebook.

1. In your own words, explain why an oscillator does not require an external input signal to produce an output.
2. Draw a simple block diagram showing an amplifier and a feedback network, indicating the path of positive feedback for an oscillator.
3. List two common applications where oscillators are used.

Lesson Keywords

• Oscillator – An electronic circuit that produces a repetitive, oscillating electronic signal without an input signal.
• Feedback – The process of returning a portion of the output signal of an electronic circuit back to its input.
• Positive Feedback – Feedback where the output signal is returned in phase with the input, reinforcing it and causing signal growth.
• Negative Feedback – Feedback where the output signal is returned out of phase with the input, reducing it and stabilizing the circuit.
• Barkhausen Criteria – Conditions (loop gain and phase shift) required for an oscillator to sustain oscillations.

Differentiation

For weaker learners, provide simplified diagrams and focus on the basic definition of an oscillator and the concept of positive feedback. For faster learners, encourage them to research different types of oscillators (e.g., RC phase shift, Wien bridge) and their specific applications.

Suggested Lesson Videos

Search on YouTube for: “Basic Electronics Oscillators and Feedback SS3”

Teacher Guide for Using This Lesson Plan

Before the lesson, ensure you have a clear chart or diagram of a basic oscillator circuit ready. Begin by linking the concept of oscillation to everyday examples to make it relatable. When explaining the principle of oscillation, emphasize the role of amplification and the feedback loop. Clearly differentiate between positive and negative feedback, highlighting why positive feedback is essential for oscillators. Encourage students to ask questions and participate in discussions. Guide them through the note-taking process, ensuring they copy the Board Summary accurately. Pay attention to students who might confuse positive and negative feedback and provide additional examples if needed. Check for understanding throughout the lesson by asking direct questions.