What is a Oscillator / Oscillation circuit?

An oscillator is an electronic circuit that generates a repetitive electrical signal at a specific frequency. The output signal of an oscillator is typically in the form of a sine wave, square wave, or triangle wave, and it is commonly used in clocks, communications, and measuring devices as a reference for timing or frequency.

Basic Principle of an Oscillator
An oscillator is able to start oscillating (generating a signal) without any external input. Its basic structure consists of an amplifier circuit and a feedback circuit.
１．Amplifier Circuit: This circuit amplifies a small signal to a larger one. Transistors or operational amplifiers are commonly used.
２．Feedback Circuit: This circuit feeds part of the output signal back to the input, enabling the oscillator to continuously generate a signal. For oscillation to persist, the feedback signal must be correctly timed and have the right amplitude when returned to the input.

Types of Oscillators
There are various types of oscillators, each with characteristics suitable for specific applications:
１．RC Oscillator: Uses resistors (R) and capacitors (C) to generate a signal. It is often used for low-frequency signals, such as in audio devices.
２．LC Oscillator: Uses inductors (L) and capacitors (C) to generate higher-frequency signals. It is commonly found in radio communication devices and radar systems.
３．Crystal Oscillator: Utilizes the vibration of a crystal to generate highly stable frequencies. It is used in clocks, computers, and other devices where precise timing is required.
４．VCO (Voltage-Controlled Oscillator): The frequency of this oscillator can be adjusted by an external control voltage. It is used in communication devices and PLL (Phase-Locked Loop) circuits.

Operating Conditions for Oscillator Circuits
For an oscillator circuit to operate stably, it must satisfy the Barkhausen criteria, which are:
１．The loop gain must be equal to 1: The feedback signal must be strong enough to maintain the input signal without attenuation.
２．The phase of the feedback signal must match the input signal: This ensures the signals resonate and the oscillation continues.

Oscillators are essential in many fields, including communication, measurement, and signal generation.

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