An Introdcution to the Voltage-Controlled Oscillator

Cecelia Qiu Cecelia Qiu 04 January
An Introdcution to the Voltage-Controlled Oscillator

Refers to an oscillator circuit (VCO) whose output frequency and input control voltage have a corresponding relationship. The frequency is an oscillator VCO whose frequency is a function of the input signal voltage. The operating state of the oscillator or the component parameters of the oscillation circuit are controlled by the input control voltage to form A voltage controlled oscillator.

Its characteristics are represented by the relationship curve between the output angular frequency ω0 and the input control voltage uc (Figure 1). In the figure, the angular frequency ω0,0 when uc is zero is called the free oscillation angular frequency; the slope K0 of the curve at ω0,0 is called the control sensitivity. In communication or measuring instruments, the input control voltage is the signal (modulated signal) to be transmitted or measured. People usually call voltage controlled oscillators as frequency modulators to generate frequency modulated signals. In the automatic frequency control loop and the phase-locked loop loop, the input control voltage is the error signal voltage, and the voltage-controlled oscillator is a controlled component in the loop.

The types of voltage-controlled oscillators include LC voltage-controlled oscillators, RC voltage-controlled oscillators and crystal voltage-controlled oscillators. The technical requirements for voltage-controlled oscillators mainly include: good frequency stability, high control sensitivity, wide frequency modulation range, linear relationship between frequency deviation and control voltage and suitable for integration. The frequency stability of the crystal voltage-controlled oscillator is high, but the frequency range is narrow; the frequency stability of the RC voltage-controlled oscillator is low and the frequency range is wide, and the LC voltage-controlled oscillator is between the two.

An Introdcution to the Voltage-Controlled Oscillator

Two major functions of voltage controlled oscillator

Voltage-controlled oscillators have their own small categories, and each category plays a very important role in production and life, so have friends summed up the basic role of voltage-controlled oscillators in the daily application process?

Use voltage controlled oscillator to control frequency

The voltage control frequency part of the high-frequency voltage-controlled oscillator is usually an LC resonant circuit formed by a varactor diode C and an inductor L. Increasing the reverse bias voltage of the varactor diode will increase the empty area in the diode. As the distance between the two conductor surfaces becomes longer, the capacitance will decrease, and the resonance frequency of the LC circuit will be increased. Conversely, when the reverse bias voltage is lowered, the capacitance in the diode becomes larger, and the frequency will be lowered.

The low-frequency voltage-controlled oscillator selects different methods according to different frequencies, such as changing the charging rate of the capacitor as a means to obtain a voltage-controlled current source. See also wave generator.

Voltage controlled crystal oscillator

A "voltage-controlled crystal oscillator (VCXO)" is usually used in the following situations: when the frequency needs to be adjusted in a small range, when the correct frequency or phase is very important for the oscillator , The use of different voltages as the control source of the oscillator, used to disperse the interference in a certain frequency range so that the frequency band is not too much affected.

The typical frequency change of a voltage-controlled quartz oscillator is between tens of ppm. This is because a high-quality factor (Quality Factor, or Q Factor) quartz oscillator will only produce a small frequency range shift.

When the radio frequency circuit transmits (transmitter) radio waves, heat is generated and the frequency drift occurs, which makes "temperature-compensated VCXO (TCVCXO)" widely used, because TCVCXO is not affected by temperature. Change its piezoelectric characteristics.

Principle of Voltage Controlled Oscillator

1. Voltage Controlled Oscillator-Introduction

Voltage-controlled oscillator, whose English name is voltage-controlled oscillator, or VCO for short, is an electronic oscillator circuit design that uses voltage input to control the oscillation frequency. The frequency or repetition ratio of its oscillation will change with the DC voltage. This feature can be used to use the modulation signal as the input of the voltage-controlled oscillator to generate different modulation signals, such as FM modulation and PM modulation. Change, PWM modulation.

2. Voltage Controlled Oscillator-Advantages

The types of voltage-controlled oscillators include LC voltage-controlled oscillators, RC voltage-controlled oscillators and crystal voltage-controlled oscillators. The technical requirements for voltage-controlled oscillators mainly include: good frequency stability, high control sensitivity, wide frequency modulation range, linear relationship between frequency deviation and control voltage and suitable for integration. The frequency stability of the crystal voltage-controlled oscillator is high, but the frequency range is narrow; the frequency stability of the RC voltage-controlled oscillator is low and the frequency range is wide, and the LC voltage-controlled oscillator is between the two.

3. Principle of Voltage Controlled Oscillator

The voltage control frequency part of the high-frequency voltage-controlled oscillator is usually an LC resonant circuit formed by a varactor diode C and an inductor L. Increasing the reverse bias voltage of the varactor diode will increase the empty area in the diode. As the distance between the two conductor surfaces becomes longer, the capacitance decreases, and the resonance frequency of the LC circuit will be increased. On the contrary, when the reverse bias voltage is reduced, the capacitance in the diode becomes larger, and the frequency will be lowered. The low-frequency voltage-controlled oscillator selects different methods according to different frequencies, such as changing the charging rate of the capacitor as a means to obtain a voltage-controlled current source.

Summarized by Easybom.

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