Refers to the oscillator circuit (VCO) whose output frequency has a corresponding relationship with the input control voltage. The frequency of the oscillator VCO is a function of the input signal voltage. The working state of the oscillator or the component parameters of the oscillation circuit is controlled by the input control voltage, which can constitute a voltage-controlled oscillator.
Its characteristics are represented by the relationship curve (Fig. 1) between the output angular frequency ω0 and the input control voltage UC. 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 to be transmitted or measured (modulated signal). People usually refer to the VCO as a frequency modulator, which is used to generate a frequency-modulated signal. In automatic frequency control loops and phase-locked loop loops, the input control voltage is the error signal voltage, and the voltage controlled oscillator is a controlled component in the loop.
The types of VCOs are LC VCO, RC VCO, and crystal VCO. The technical requirements for the VCO mainly include good frequency stability, high control sensitivity, wide frequency modulation range, linear relationship between frequency offset and control voltage, and suitability for integration. The frequency stability of the crystal VCO is high, but the frequency modulation range is narrow; the frequency stability of the RC VCO is low the frequency modulation range is wide, and the LC VCO is in the middle.
VCO has two functions
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?
Use a voltage controlled oscillator to control the frequency
The voltage-controlled 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. When the reverse bias voltage of the varactor diode is increased, the void area in the diode will increase, the distance between the two conductor surfaces will become longer, the capacitance will decrease, and the resonant frequency of the LC circuit will be increased. Conversely, when the reverse bias voltage is reduced, the capacitance in the diode becomes larger and the frequency decreases.
On the other hand, the low-frequency voltage-controlled oscillator selects different methods according to different frequencies, for example, a voltage-controlled current source is obtained by changing the charging rate of the capacitor. See Waveform Generator.
Voltage Controlled Crystal Oscillator
A “voltage-controlled crystal oscillator (VCXO)” is typically used when the frequency needs to be adjusted within a small range when the correct frequency or phase is important to the oscillator, Using different voltages as the oscillator of the control source, used to disperse the interference in a certain frequency range, so that the frequency band is not greatly affected.
The typical frequency variation of a VCO is in the tens of ppm because a quartz oscillator with a high-quality factor (or Q Factor) produces only a small amount of frequency range shift.
When the radio frequency circuit transmits (transmitter) radio waves, heat will be generated and frequency drift will occur, which makes “temperature-compensated VCXO (TCVCXO)” widely used because TCVCXO will not be affected by temperature. change its piezoelectric properties.
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