Voltage-controlled oscillator
The voltage controlled oscillator as a VCO ( Voltage- Controlled Oscillator English ) are known, there is an electrical oscillator, whose frequency can be the size of an applied voltage ( control or regulating voltage ) is changed.
Design and operation
The construction of a VCO depends largely on the operating frequency and the required parking area.
VCOs for high frequencies can be realized mainly by an oscillator circuit whose frequency determining elements can be electrically varied. This is achieved for example by use of a variable capacitance diode in the frequency-determining resonant circuit, whose resonant frequency can be changed by varying the diode bias voltage thereby. VCOs with diode vote a vote over a frequency range of up to about 3:1, and the quality of the output signal (noise, stability) decreases with increasing variation range. If instead of an LC resonant circuit uses a quartz crystal oscillator (VCXO, english voltage -controlled x - tal oscillator), the tuning is usually only a few thousand of the working frequency.
VCO for very high frequencies (microwave range) often use as a frequency determining element of a resonant circuit in place of a YIG resonator whose resonance frequency can be changed by variation of the ambient magnetic field (that is, by altering the coil current of an electromagnet ).
In the region of lower frequencies, there are a variety of circuit arrangements, which can generate variable frequencies. These are often based on an integrator, the input corresponds to the control voltage, and which is reset upon reaching a threshold voltage. Such circuits can be relatively large frequency ranges ( frequency variation by several orders of magnitude ) can be realized.
Application
Electronic Music
In the electronic music VCOs are used as an assembly of synthesizers. In modular synthesizers has since the late 1960s, the exponential control established itself as a de facto standard, which was developed by Robert Moog for his modular synthesizer. To this end, the circuit is designed so that an increase in the input voltage to a voltage having a frequency double of the output result, so an increase of one octave. Therefore, this control is specified in volts per octave.
As the technical design with analog electronics has some difficulties (in particular high temperature sensitivity ) was used by the Japanese company Korg and Yamaha for low-cost devices such as the Korg MS-20 is a linear control of Hz / Volt. These devices can then be used without further with devices with exponential activation in a musical context.
Usually VCOs are designed so that they can generate different waveforms ( square, triangle, sawtooth and various other ) and allow a pulse width modulation of the square wave. Moreover, there is in addition to the VCOs allow exponential characteristic of a linear drive. Thereby the generation of frequency modulation (FM synthesis) is also possible. Last is as musically important element of VCO nor the synchronization ( sync english hard, soft sync) mentioned.
Electronics
The VCO is an element of a PLL circuit ( Phase Locked Loop English ). It is here the actuator and generates a regulated with a feedback loop frequency. Applications include stereo decoder, motor control and PLL decoder.
Furthermore, using superheterodyne receiver voltage-controlled oscillators ( oscillating circuits with capacitance diode ) to set the receive frequency ( frequency tuning of the local oscillator ).
VCO, the output a square wave, are used for example in sensor circuits or sensors downstream to transmit the output signal with two voltage levels smoothly and be able to process, for example, in a microcontroller. The information do not put it in the signal level, but in a continuously variable frequency. This here not a digital signal; This occurs only when the frequency is measured by counting a fixed time.
An accurate voltage to frequency converter integrated circuit is for instance the LM331. It can also be used as a frequency -to-voltage converter. If no precision is required, there is also a ring oscillator can be used.