VCO Voltage Controlled Oscillator Circuit Simulation
Voltage controlled oscillator is a type of oscillator where the frequency of the output oscillations can be varied by varying the amplitude of an input voltage signal. Voltage controlled oscillators are commonly used in frequency (FM), pulse (PM) modulators and phase locked loops (PLL).
Another application of the voltage controlled oscillator is the variable frequency signal generator itself.
Voltage controlled oscillators can be broadly classified into a linear voltage controlled oscillators and relaxation type voltage controlled oscillators. Linear voltage controlled oscillators are generally used to produce a sine wave.
Relaxation-type voltage controlled oscillators are used to produce a sawtooth or triangular waveform. This is achieved by the gradual charging and sudden discharge of a capacitor connected appropriately to an active element (UJT, PUT etc) or a monolithic IC (LM566 etc). Nowadays relaxation type VCOs are generally realized using monolithic ICs. The circuit diagram of a voltage controlled oscillator using LM566 is shown in the figure below.
Voltage controlled oscillator using LM566 IC
Typical applications of LM566 IC are signal generators, FM modulators, FSK modulators, tone generators etc. The LM566 IC can be operated from a single supply or dual supply. While using a single supply, the supply voltage range is from 10V to 24V. The IC has a very linear modulation characteristic and has excellent thermal stability.
1. Resistor – 4.7k ohm – 1 no
2. Resistor – 2.2k ohm – 1 no
3. Resistor – 10k ohm – 1 no
4. IC – LM566 – 1 no
5. Capacitor – 47nF – 1 no
6. Capacitor – 1nF – 1 no
Resistor R1 and capacitor C1 form the timing components. Capacitor C2 is used to prevent the parasitic oscillations during VCO switching. Resistor R3 is used to provide the control voltage Vc. Triangle and square wave outputs are obtained from pins 4 and 3 respectively. The output frequency of the VCO can be obtained using the following equation:
Fout = 2.4(V+-V5) /(R1C1V+) . Where Fout is the output frequency, R1 and C1 are the timing components and V+ is the supply voltage.