Tanssion > blog > oscillator > Oscillator Classification Introduction

# Oscillator Classification Introduction

Author: Tanssion Date: 2023-07-26 Hits: 0

An oscillator is an electronic device or circuit that produces a periodic oscillating signal or waveform. It oscillates or fluctuates repeatedly in forward and reverse directions at a fixed frequency.

An oscillator is an energy conversion device that converts DC power into AC power with a certain frequency, and the circuit it forms is called an oscillator circuit.

It usually consists of an amplifier circuit, a frequency selection network, a positive feedback network and an amplitude stabilization link. Oscillators convert the direct current (DC) supplied by the power supply into an alternating current signal. They are widely used in many electronic devices. Common examples of signals produced by oscillators are the signals broadcast by radio and television transmitters, the signals used to adjust the clocks of computers and quartz clocks, and the sounds produced by electronic pagers and video games.

Ⅰ. Basic Components of an Oscillator

1. Amplifier: Responsible for amplifying the signal to overcome the loss of the oscillator and provide the gain required by the feedback network. The amplifier is usually an amplifier tube or amplifier circuit that increases the strength of the oscillator's output signal, ensuring sufficient amplification of the feedback signal to sustain oscillation. Can play the role of energy control.

2. Feedback network: The most important part of the oscillator is the feedback network, which is a closed-loop system that re-inputs part of the output signal to the input of the oscillator, thereby maintaining the continuous oscillation of the oscillator. It is responsible for reintroducing part of the output signal to the input of the oscillator so that the system maintains self-sustained oscillation. The feedback network determines the frequency and stability of the oscillator. Common feedback networks include RC networks, LC networks, and resonant circuits in crystal oscillators.

3. Frequency stabilization components: Frequency stabilization components are key elements that determine the output frequency of the oscillator. Usually an inductor, capacitor, or crystal that determines the operating frequency of the oscillator. Crystals used in crystal oscillators have highly stable frequency characteristics.

Ⅱ. The working principle of the oscillator

An amplifier is needed in an oscillator to provide sufficient gain to ensure that the feedback signal is amplified and drives the system to continue oscillating. The amplifier is a key element in an oscillator, it amplifies the input signal to a sufficient level to compensate for losses in the oscillator and feedback loop.

The key to an oscillator is the feedback loop. The feedback loop feeds a portion of the oscillator's output signal back to the input, forming a closed-loop system. This feedback signal will be amplified by the amplifier, and then input to the oscillator again, prompting the system to continue to oscillate.

The signal in the feedback loop needs to have a positive phase characteristic, so that the output signal and the input signal of the system can be kept in phase, so as to achieve the effect of positive feedback. Positive feedback means that the output signal strengthens the input signal so that the system develops towards a specific oscillation state instead of decaying or decaying to zero.

Oscillators also require a frequency stabilizing element (such as capacitors, inductors, crystals, etc.), which determines the output frequency of the oscillator. In an oscillator, a frequency stabilizing element is coupled with an amplifier and a feedback network to create a resonant condition that causes the oscillator to oscillate at a specific frequency.

When the oscillator starts working, the system produces a tiny output signal due to tiny noise or interference. This output signal is re-input into the feedback loop of the oscillator after passing through the amplifier. The amplified signal again drives the oscillator and is superimposed on the input signal. The effect of the amplification results in an increase in the output signal. This process is repeated until the system reaches a stable oscillation state where the amplitude and phase of the output signal remain constant within each cycle. In this way, the oscillator can generate a stable periodic signal, that is, an oscillating signal.

Ⅲ. Relaxation oscillator

Is a special type of oscillator that is based on periodic switching between charging and discharging processes. Unlike other common resonant oscillators, the output signal of a relaxation oscillator is a non-sinusoidal waveform, usually a square or sawtooth wave. Oscillators that output sawtooth waves are commonly used to generate horizontal reflection signals in oscilloscopes or in cathode ray tubes in televisions, relative to time. In frequency generators, triangular waves are also commonly used for shaping to output signals close to sine waves.

The relaxation oscillator contains nonlinear devices such as transistors, which can periodically release the energy stored in the capacitor or inductor, causing the output signal waveform to change instantaneously.

How relaxation oscillators work:

1. Charging phase: In the charging phase of the oscillator, a capacitor is charged through a charging circuit. During charging, the voltage across the capacitor gradually increases until it reaches a threshold voltage.

2. Discharge phase: Once the voltage of the capacitor reaches the threshold voltage, it will switch to the discharge phase. During discharge, the capacitor is discharged through a discharge circuit. The voltage across the capacitor gradually decreases until it reaches another lower threshold voltage.

3. Repeat cycle: Once the voltage of the capacitor drops to the lower threshold, the charging phase starts again and the whole process repeats periodically. Therefore, the output signal of the oscillator is a periodic square wave or sawtooth waveform.

What the relaxation oscillator does:

1. For audio generator: The output of the relaxation oscillator can be used to generate an audio signal. It is widely used in some audio applications, such as sound synthesis and music synthesis.

2. For pulse generator: The square wave output of the relaxation oscillator can be used as a pulse generator to control the work of other electronic components or circuits. Pulse generators are found in digital circuits, communication systems, and control systems.

3. For timer and clock circuits: Relaxation oscillators can be used as simple timer and clock circuits. They produce a periodic square or sawtooth waveform output that can be used to measure time, generate clock pulses, and provide a reference clock signal for other electronic systems.

4. For frequency dividers: The output frequency of the relaxation oscillator is usually higher. Dividing high frequency signals into lower frequency signals can be achieved by connecting its output to an appropriate frequency divider circuit.

5. For signal modulation: In some communication applications, the output of the relaxation oscillator can be used to modulate the signal. Amplitude modulation or frequency modulation can be achieved by multiplying the oscillator output with the signal to be transmitted.

Ⅳ. Harmonic Oscillator

A harmonic oscillator is a special type of oscillator that generates harmonic signals through a resonant circuit. The main feature of a harmonic oscillator is that the output signal contains harmonic components that are integer multiples of the fundamental frequency, usually the second harmonic, third harmonic, fourth harmonic, etc. These harmonic components are multiples of the fundamental frequency with progressively decreasing amplitudes and increasing frequencies.

The role of the harmonic oscillator:

1. Used in radio frequency equipment: Harmonic oscillators are widely used in radio frequency equipment to generate high frequency oscillation signals, such as in radio frequency communication, radar and satellite communication systems.

2. Used in signal generators: Harmonic oscillators can be used as signal generators to generate periodic signals of different frequencies for laboratory testing, signal debugging, etc.

3. Used in measuring instruments: In various measuring instruments, harmonic oscillators are often used as reference clocks or frequency standards to ensure the accuracy and reliability of measurements.

4. Used in frequency synthesizers: Harmonic oscillators can be used in frequency synthesizers. By generating harmonic signals, an output signal of a desired frequency can be generated. By adjusting the resonance circuit parameters of the harmonic oscillator, different output frequencies can be achieved.

Harmonic oscillators are mainly divided into feedback oscillators and negative resistance oscillators.

Feedback oscillator

The most common form of a linear oscillator is an electronic amplifier (such as a transistor or operational amplifier), the output of which is fed back through a feedback network to the input of a frequency selective filter. The moment the amplifier's power is applied, there is only noise at the output of the amplifier. These noises are passed to a narrow-band filter, so that a specific part of the frequency in the noise is filtered out and appears at the output of the filter.

A feedback oscillator is a type of oscillator whose operation is based on a positive feedback loop. The key to feedback oscillators is positive feedback. Positive feedback means that the signal returned from the output to the input is amplified and strengthened in the feedback loop. Such feedback causes the system to self-sustain, rather than decay or decay to zero.

Feedback oscillators are classified according to the type of frequency selective filter used in the feedback circuit:

1. In the LC oscillator circuit, the filter is a tuned circuit, and the charge flows back and forth between the plates of the capacitor, so that the tuned circuit can store electric energy oscillating at its resonant frequency. There will be small losses in the tank, but the amplifier compensates for these losses and provides power to the output signal. LC oscillators are commonly used at radio frequencies when a tunable frequency source is required, such as in local oscillators in signal generators, tunable radio transmitters, and radio receivers. Typical LC oscillator circuits are Hartley oscillator, Colpitts oscillator and Clapp oscillator.

2. In an RC oscillator circuit, the filter is a network of resistors and capacitors. RC oscillators are mainly used to generate lower frequencies, such as in the audio range. Common types of RC oscillator circuits are phase shift oscillators and Wien bridges.

3. In a crystal oscillator circuit, the filter is a piezoelectric crystal. The crystal resonator vibrates mechanically, and its vibration frequency determines the oscillation frequency. The crystal has a high Q value, and its temperature stability is better than that of a tuned circuit, so the frequency stability of a crystal oscillator is much more stable than that of an LC or RC oscillator.

Negative resistance oscillator

Is a special type of oscillator whose operating principle involves negative resistance effects. Normally, the current and voltage across the resistor are in phase, which means the resistance of the resistor is positive. However, certain electronic components (such as certain diodes, transistors, laser diodes, etc.) can exhibit a negative resistance effect under certain conditions. The negative resistance effect means that there is a 180 degree phase difference between the current and voltage, resulting in a negative resistance. Negative resistance oscillators use the negative resistance effect as part of a feedback loop. The feedback loop of the negative resistance oscillator feeds back a part of the output signal to the input terminal, and this feedback signal passes through the negative resistance effect under certain conditions, causing the output signal to be amplified instead of attenuated.

Ⅴ. Classification of Oscillators

1. According to the vibration excitation points:

Externally excited oscillator

Self-excited oscillator: is a feedback control system. The characteristic is that oscillation can be generated without an external excitation signal. It is a self-sustaining oscillator that generates a continuous periodic oscillation signal through an internal positive feedback loop. A self-oscillating oscillator contains a positive feedback loop that feeds a portion of the oscillator's output signal back to the input. This feedback signal is amplified by the amplifier and re-input into the oscillator to produce a positive feedback effect. Due to the existence of positive feedback, the output signal generates self-sustained oscillation in the process of being continuously fed back and amplified. The oscillator will continuously output a periodic signal without the need for an external excitation signal.

2. According to the output waveform:

Sine wave oscillator: is an oscillator that produces a sine wave output signal. The sine wave oscillator is a special type of oscillator whose main feature is that the waveform of the output signal is a pure sine wave. Sine wave oscillators are used in communication systems as reference clocks and frequency synthesizers; they are also used in test and measurement instruments to provide accurate test signals.

Sawtooth oscillator: It is an oscillator that produces a sawtooth waveform output signal. A sawtooth oscillator is a special type of oscillator whose output waveform exhibits a waveform that resembles a sawtooth. In a sawtooth oscillator, with proper circuit design, the oscillator is charged and discharged periodically. In each cycle, the oscillator ramps up linearly from the initial value at a certain rate, and then quickly returns to the initial value. Sawtooth oscillators are used in oscilloscopes to generate test signals for measuring and observing the response of circuits.

Square wave oscillator: It is an oscillator that produces a square wave output signal, which jumps quickly from low level to high level, and then quickly jumps back to low level. In digital circuits and computer systems, square wave oscillators can be used as a clock source to provide a stable square wave clock signal for synchronizing the operation of various components; in communication systems and modems, square wave oscillators are used to generate modulation signals , for example for Frequency Shift Keying (FSK) modulation.

Pulse oscillator: It is an oscillator that generates a pulse waveform output signal. A pulse oscillator is a special type of oscillator whose output waveform is pulse-like. The waveform characteristics of a pulse oscillator contain rich harmonic components, and its spectrum contains harmonics of various frequencies.

3. According to the circuit structure:

Inductance-capacitance oscillator: It is a common type of oscillator. It uses an inductor and a capacitor to form a resonant circuit to generate a periodic oscillation signal. It is also called an LC oscillator.

Common LC oscillators include: Hartley oscillator, Colpitts oscillator, LC sine wave oscillator, RC phase shift oscillator. LC oscillators are widely used in various electronic devices and communication systems, especially in the low frequency, medium frequency and radio frequency ranges.

Tuning fork oscillator: It is an oscillator that uses the mechanical vibration of a tuning fork to generate a periodic signal. A tuning fork is a resonant structure with a specific frequency, usually made of metal, and shaped like a small fork. When a tuning fork is excited or disturbed by an external force, it vibrates at a specific frequency and produces sound during the vibration. A tuning fork can be actuated by tapping or by other means, such as tapping it with a finger or touching it with a string. A tuning fork produces sound during vibration, which is determined by its vibration frequency. At the same time, the tuning fork oscillator can also convert the mechanical vibration into an electrical signal through a suitable sensor, thereby outputting a periodic electrical signal waveform.

Resistance-capacitance oscillator: It is a common type of electronic oscillator, which uses a resonant circuit composed of resistance and capacitance to generate an oscillation signal. The resonant circuit of the RC oscillator consists of resistors and capacitors, which together determine the frequency of the oscillator. During the operation of the oscillator, the capacitor is charged and discharged periodically, and the resistor controls the rate of charge and discharge. Common types of RC oscillators include: RC pulse oscillator, RC sine wave oscillator, and RC square wave oscillator.

Crystal Oscillator: It is a highly stable and precise oscillator that uses the resonant properties of a crystal to generate a precise periodic oscillating signal. Crystal oscillators contain a resonating crystal, usually a quartz crystal, inside. Crystals have a specific resonant frequency, that is, they have resonant properties at a specific frequency. When a voltage is applied to the crystal, it creates mechanical vibrations that cause the crystal to oscillate around its resonant frequency.

LC oscillator: The LC oscillator is a resonant oscillator that uses an inductor and capacitor to form a resonant circuit to generate a periodic oscillating signal. The frequency of the LC oscillator depends on the values of the inductor and capacitor, which are key parameters in the design. Adjusting the values of the inductance and capacitance can realize oscillation signals of different frequencies. LC oscillators are very useful in some specific applications, especially in the low and mid frequency range.

RC Oscillator: RC oscillators are usually used for low-frequency oscillation, and the frequency is generally in the range of a few hertz (Hz) to hundreds of kilohertz (kHz). They are widely used in various electronic equipment and communication systems, especially in applications that need to generate low-frequency clock signals, frequency synthesizers, and sound wave generators.

4. By frequency range:

Low-frequency oscillator: It is a type of oscillator that generates low-frequency oscillation signals. Low-frequency oscillators generally refer to oscillators whose oscillation frequency ranges from Hertz to several hundred kilohertz.

Intermediate frequency oscillator: It is an oscillator that generates intermediate frequency oscillation signals. Usually between tens of kilohertz to hundreds of megahertz. The IF oscillator generates a stable IF oscillation signal in this frequency range for applications such as modulation and demodulation, frequency conversion, and signal processing.

High-frequency oscillator: It is an oscillator that generates high-frequency oscillating signals. High-frequency oscillators generally refer to oscillators with oscillation frequencies in the megahertz to hundreds of gigahertz range. Common types of high-frequency oscillators include: feedback oscillators, crystal oscillators, voltage-controlled oscillators, microwave oscillators, etc.

Microwave Oscillators: Microwave oscillators need to have a highly stable frequency in the high frequency range to ensure reliable transmission and communication of signals. Microwave oscillators play an important role in applications such as high-frequency microwave communications, radar systems, satellite communications, and radio frequency equipment.

Variable Frequency Oscillator (VCO): It is a special type of oscillator whose output frequency can be adjusted and controlled in real time by adjusting an external voltage. The VCO contains a voltage control element inside, usually a diode, a field effect transistor or a voltage-controlled oscillator circuit. The characteristic of this component is that when the external voltage is adjusted, its resonant frequency also changes accordingly. When the external voltage changes, the characteristics of the voltage control element will cause the resonant frequency to change accordingly, so that the output frequency of the VCO will change accordingly.

Fixed Frequency Oscillator: An oscillator whose output frequency is fixed and cannot be changed by external adjustment or control. The output frequency of a fixed-frequency oscillator is preset and fixed at a specific value, and the output frequency cannot be changed by external means (such as adjusting the voltage). Fixed frequency oscillators are usually designed with high frequency stability to ensure that their output frequency remains constant during use regardless of factors such as temperature and supply voltage.

6. Programmable oscillator

Programmable oscillators can adjust the output frequency within a certain range, which is flexible and adaptable for applications that require frequency variability. The output frequency of the programmable oscillator can be adjusted in real time by programming. By changing the control parameters of the oscillator, such as programming registers or configuration registers, the output frequency can be changed. Programmable oscillators are widely used in applications such as communication systems, frequency synthesizers, clock sources, software defined radios, test equipment, etc.

Programmable Oscillator, Conventional Oscillator of Any Frequency Generates any frequency via programmable phase-locked loop (PLL), frequency division, output accumulation, and output buffering. Programmable oscillators can be used as a reference frequency for other systems to synchronize or calibrate other oscillators or clock sources.

1、Is the frequency of the oscillator adjustable?
The frequency of the oscillator can be adjustable. Some oscillators are designed as fixed frequency oscillators, whose output frequency is preset and fixed at a specific value and cannot be changed by external adjustment or control. However, there is also a special type of oscillator designed as a variable frequency oscillator (VCO), whose output frequency can be adjusted in real time by adjusting an external voltage.
2、How does the stability of oscillators compare?
Comparisons can be made by frequency offset, temperature stability, frequency drift, phase noise, and supply voltage stability.
3、What are the frequency ranges of oscillators?
The frequency range of an oscillator can cover a wide range from low frequencies to high frequencies. The frequency ranges of common oscillators include optical oscillators, millimeter wave oscillators, low frequency oscillators, intermediate frequency oscillators, high frequency oscillators, etc.

## Related Articles

• #### Oscillator Classification Introduction

An oscillator is an electronic device or circuit that produces a periodic oscillating signal or wave