Electronic Oscillators

Introduction

• Discussion about electronic oscillators.
• Used in various applications:
  • Laptop and smartphone processors for clock signals.
  • Radio and mobile receivers for local carrier frequency.
  • Signal generators in labs for circuit testing.

Basic Working Principle

• Oscillator converts DC voltage to periodic AC signal.
• Frequency range: Few Hz to GHz.
• Output can be:
  • Sinusoidal signals.
  • Non-sinusoidal signals (square wave, triangular wave).

Oscillator Components

• Basic oscillator circuit: Amplifier with positive feedback.
• Input sinusoidal signal is amplified:
  • Output = A × Input Signal.
• Feedback circuit: Typically a frequency selective or resonant circuit.
  • Feedback voltage (Vf) = β × Output Voltage.
  • β represents feedback fraction.

Loop Gain and Sustained Oscillations

• Loop gain (Aβ) determines oscillation stability:
  • If Aβ < 1: Oscillations die out over time.
  • If Aβ > 1: Oscillations build up.
  • If Aβ = 1: Sustained oscillations occur.

Barkhausen's Criteria

• For sustained oscillations:
  1. Aβ must equal 1.
  2. Phase shift should be zero.

Noise and Oscillation Generation

• Oscillations can occur without an applied input signal due to:
  • Thermal noise in the circuit.
• Thermal noise contains all frequency components:
  • Amplified by the oscillator.
  • Feedback circuit selects one frequency for oscillation.
• Non-linear behavior of amplifier or feedback circuit helps achieve Aβ = 1.

Mathematical Proof of Criteria

• Output of feedback circuit (Vf) added to input (Vin):
  • Input to amplifier = Vin + Vf.
  • Output = A × (Vin + Vf).
• Simplifies to:
  • Vout/Vin = A / (1 - Aβ).
• Sustained oscillations require Aβ = 1.

Types of Feedback Circuits

• Feedback circuit materials:
  • RL, RC, or RLC components.
  • Quartz crystals for frequency selection.
• Classifications of oscillators:
  • Sinusoidal oscillators (harmonic): Output as sine wave.
  • Relaxation oscillators: Output as square or triangular wave.
    • Can be built using op-amp or timer ICs (e.g., 555 timer).

Conclusion

• Summary of the basic working principle of oscillators.
• Invitation for questions and video engagement.