 Home Oscillator  Dec 11 2018

# What Is An Oscillator Circuit ?

## Introduction

An oscillator is an electronic component used to generate a repeating electronic signal (usually a sine or square wave). The circuit that constitutes it is called an oscillating circuit. An electronic circuit or device capable of converting direct current into an output of an alternating current signal having a certain frequency. There are many types, according to the oscillation excitation mode, it can be divided into self-excited oscillator and other oscillator; according to the circuit structure, it can be divided into RC oscillator, inductor-capacitor oscillator, crystal oscillator, tuning fork oscillator, etc. It is an oscillator such as a sine wave, a square wave, or a sawtooth wave. Widely used in electronics industry, medical, scientific research and other aspects.

 Article Core Oscillator Circuit Purpose Introduce what the oscillator circuit is. Application Electronics industry, medical, scientific research and so on. Keywords Oscillator Circuit

## What is Oscillator Circuit?

An amplifying circuit that has an output signal at the output with an input signal at the input. If there is no external input signal at the input end, the output terminal still has a certain frequency and amplitude signal output. This phenomenon is called self-oscillation of the amplifying circuit. The oscillating circuit is a circuit that generates a sine wave output voltage by self-oscillation of the circuit without an external input signal. It is widely used in remote control, communication, automatic control, measurement and other equipment, and also as a test signal for analog electronic circuits.

What is an oscillator?

## How Does the Oscillator Circuit Works?

### 1. Conditions for Generating Sinusoidal Oscillation

The sinusoidal oscillation circuit shown in Figure 1 is a positive feedback closed-loop circuit without input signal. Figure1. Block Diagram of Sinusoidal Oscillation Circuit

### 2. Establishment and Stability of Sinusoidal Oscillation

The initial signal of an actual sine wave oscillating circuit is caused by disturbances in the internal noise of the circuit and transient processes. Usually the spectrum of these noises and disturbances is very wide and small. In order to finally obtain a stable sinusoidal signal, first, a frequency selective link must be used to select the component of the desired frequency from the noise or disturbance signal to satisfy the phase balance condition, and the other frequency components do not satisfy the phase balance condition. Secondly, in order to enable the oscillation to be established from small to large, it is required to meet.

### 3. Composition of Sinusoidal Oscillation Circuit

It can be seen from the above analysis that the sine wave oscillation circuit must have the following four basic steps in terms of composition.

(1) Amplification circuit: to ensure that the circuit can be from the start-up to the dynamic balance process, the circuit obtains a certain amplitude output and realizes energy control.

(2) Frequency selection network: Determine the oscillation frequency of the circuit, so that the circuit generates oscillation of a single frequency, that is, the circuit generates sinusoidal oscillation.

(3) Positive feedback network: Introduce positive feedback so that the input signal of the amplifying circuit is equal to the feedback signal.

(4) Stable link: that is, the nonlinear link, the role is to stabilize the output signal amplitude.

In many practical circuits, the frequency-selective network and the positive feedback network are often combined into one. Moreover, for the discrete component amplifying circuit, there is no additional stabilization link, and the nonlinearity of the transistor characteristics is stabilized. effect.

Sinusoidal oscillation circuit is usually named according to the components used in frequency selection network. It can be divided into three types: RC sinusoidal oscillation circuit, LC sinusoidal oscillation circuit and quartz crystal sinusoidal oscillation circuit. RC sinusoidal oscillation circuit oscillation frequency is low, generally below 1 MHz; LC sinusoidal oscillation circuit oscillation frequency is high, generally above 1 MHz; quartz crystal sinusoidal oscillation circuit can also be equivalent to LC sinusoidal oscillation circuit, its characteristics are very stable oscillation frequency.

## What Role Does the Oscillator Play in the Circuit?

One of the most common oscillators is the pendulum of the clock. If you push the pendulum to start oscillating, it will oscillate at a certain frequency - it will swing back and forth every second for a certain number of times. The main frequency of control is the length of the pendulum.

To oscillate an object, energy must be converted back and forth between the two forms. For example, in a pendulum, energy is converted between potential energy and kinetic energy. When the pendulum is at the end of the swing, its energy is all potential energy and is ready to fall. When the pendulum is in the middle of the loop, all potential energy is converted to kinetic energy and the pendulum moves at the fastest speed. When the pendulum moves to the other side, all the kinetic energy turns into potential energy. The conversion of energy between these two forms is the cause of the oscillation.

Finally, any physical oscillations will stop due to friction. To continue exercising, you must add a little energy to each cycle. In the pendulum clock, the energy that keeps the pendulum moving comes from the spring. The pendulum gets a little thrust every time it rings to compensate for the energy lost by friction. Figure2. Pendulum Movement

Oscillators are electronic components used to generate repetitive electronic signals (usually sinusoidal or square waves). Its circuit is called oscillating circuit.

Low frequency oscillator is an oscillator that generates AC signals between 0.1 Hz and 10 Hz. This word is usually used in audio synthesis to distinguish other audio oscillators.

The oscillator can be divided into two kinds: harmonic oscillator and relaxation oscillator.

According to the mode of oscillation excitation, it can be divided into self-excited oscillator and other-excited oscillator.

According to the circuit structure, it can be divided into resistance-capacitance oscillator, inductance-capacitance oscillator, crystal oscillator and tuning fork oscillator.

According to the output waveform, it can be divided into sine wave, square wave and sawtooth wave oscillators.

Self-excited multivibrator is also called unsteady circuit. Each collector of the two tubes has a capacitor connected to the base of the other tube, which acts as AC coupling and forms a positive feedback circuit. When the power supply is switched on, one tube opens first and the other tube cuts off. At this time, the collector of the conducting tube has an output, and the capacitance of the collector couples the pulse signal to the other tube. The base leads the other tube through. At this time, the original tube was cut off. In this way, the two tubes turn on and off, resulting in oscillating current. Figure3. Self-excited Multivibrator

Since the parameters of the device are not completely identical, the state of the two transistors changes at the moment of power-on. This change is caused by the positive feedback, which leads to a transient steady state. During the transient steady state, the other transistor is turned on or off after being gradually charged by the capacitor, and the state is turned over to reach another temporary steady state. This cycle begins to oscillate.

The oscillator is a frequency source and is typically used in phase-locked loops. It is a device that can convert DC power into AC energy without external signal excitation. It has many uses. Electromagnetic waves are generated in radio broadcast and communication equipment. A clock signal is generated in the microcomputer. High frequency alternating current is generated in the voltage stabilizing circuit.

## What Are the Basic Component of Oscillator?

1. Triode amplifier; (from the energy control role)

2. Positive feedback network; (feed back part of the output signal to the input)

3. Frequency selection network; (to select the required oscillation frequency, so that the oscillator can oscillate at a single frequency, thereby obtaining the required waveform self-excited multivibrator also called an unsteady circuit. Each of the collectors has a capacitor connected to the base of the other tube to form an AC coupling function, forming a positive feedback circuit. When the power is turned on, one of the tubes is turned on first, and the other tube is turned off. At this time, the oscillation is performed. The collector of the conduction tube has an output, and the capacitance of the collector is coupled to the base of the other tube to turn on the other tube. At this time, the originally turned-off tube is turned off, so that the two tubes are turned on and At the cutoff, an oscillating current is generated.

Since the parameters of the device are not completely identical, the state at the moment of power-on has changed. The change of the oscillator is more and more intense due to the positive feedback, resulting in a transient steady state. During the transient steady state, the other transistor is turned on or off after being gradually charged by the capacitor, and the state is turned over to reach another temporary steady state. This cycle begins to oscillate.

A low frequency oscillator is an oscillator that generates an alternating current signal between 0.1 Hz and 10 Hz. This term is often used in audio synthesis to distinguish other audio oscillators. Figure4. A Low Frequency Oscillator

## What Are the Classic Design of Oscillating Circuit?

### RC Oscillator

A circuit composed of RC components is used as a sine wave oscillating circuit of a frequency selective network, which is called an RC oscillator. According to the structural characteristics of the feedback network, the RC oscillator circuit can be divided into an oscillating circuit of RC phase shifting type, RC bridge type and double T type frequency selective network. The RC bridge type oscillation circuit uses the RC series-parallel circuit as the frequency selection network, so it is also called the RC series-parallel oscillation circuit, as shown in Fig. 4. Figure5. RC Oscillator

This circuit consists of two parts, the amplifier Au and the frequency selective network Fuo Au is a voltage series negative feedback amplifier composed of integrated operational amplifiers, while the Fu is composed of Zl and Z2, and also serves as a positive feedback network. Zl, Z2 and Rl, R2 form a four-arm bridge. The input and output of the amplifier circuit are respectively connected to the two diagonals of the bridge. Therefore, this RC oscillator circuit is also called RC bridge oscillator.

### RC Phase-shifted Sinusoidal Oscillation Circuit

The RC phase shift sine wave oscillating circuit uses the RC phase shifting network as a feedback link of the sine wave oscillating circuit, as shown in FIG. The RC phase shifting network of the oscillating circuit provides a phase shift of 180° solution, and the amplifier uses an inverting input proportional amplifying circuit, so φa=-180. , φa + φf = 0 ° to meet the phase condition of the oscillation, as long as the thermistor Rf is adjusted so that the amplification factor is sufficient to compensate for the signal amplitude attenuation caused by the feedback network, a sinusoidal oscillation signal can be generated. Figure6. RC Phase-shifted Sinusoidal Oscillation Circuit

### Transformer Feedback LC Oscillator

The feedback network uses a transformer, and the primary winding of the transformer is connected in parallel with the capacitor to form an oscillating circuit as a frequency selective network, instead of the transistor collector resistor Rc, the feedback voltage is drawn back from the secondary winding of the transformer and applied to the input end of the amplifying circuit, the circuit As shown in Figure 6. Figure7. Transformer Feedback LC Oscillator

The characteristics of the transformer feedback LC oscillating circuit are that the oscillating frequency is easy to adjust, and it is easy to achieve impedance matching and achieve the requirements for starting vibration. The output waveform is generally low, and the frequency stability is not high. The frequency of generating a sine wave signal is several kilohertz to several tens of megahertz. Suitable for less demanding equipment.

### Inductive Three-point Oscillator

A typical circuit for an inductive three-point oscillator is shown in Figure 8. In the LC tank circuit, the inductor has a tap to divide the coil into two parts, namely coil L1 and coil L2, the 3 terminal of coil L1 is connected to the base B of the transistor, and the 1 terminal of coil L2 is connected to the collector C of the transistor, and the center tap 2 Connect the emitter E. That is to say, the three ends of the inductor are respectively connected to the three poles of the transistor, so it is called an inductor three-point oscillator, also known as a Hartley oscillator. Figure8. Inductive Three-point Oscillator

In this circuit, L1 doubles as a feedback network, and the L1 feedback voltage is applied to the input terminal of the transistor through the coupling capacitor C1. After amplification, the high-frequency oscillation signal is obtained in the LC oscillation circuit, as long as the position of the inductor coil is properly selected. By making the feedback signal larger than the input signal, an un-attenuated equal-amplitude oscillation can be obtained in the LC loop.

The oscillation frequency can be obtained by the following formula: In the formula, L1 and L2 are the self-inductance coefficients on both sides of the coil tap; M is the tile inductance of the two-stage inductor; C is the oscillation capacitor; and o is the oscillation frequency.

### Capacitive Three-point Oscillator

Fig. 9 is a typical circuit diagram of a capacitive three-point oscillator. Its structure is similar to that of an inductive three-point oscillator, except that L and C are interchanged. In the LC oscillation circuit, two capacitors are connected in series to form a capacitor branch. There is a lead-out end between the two capacitors. A part of the voltage is fed from the capacitor branch of the LC tank to the input end of the amplifier circuit through the lead-out terminal. They are connected to the three poles of the transistor, so this circuit is called a three-point LC oscillator, also known as a Colpitts oscillator. Figure9. Capacitive Three-point Oscillator

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