Simple Voltage Controlled Oscillator Circuit

Visualize a gadget that makes sounds like a whistle, but you can control how high or low the pitch is with a knob.

That is kind of what a voltage controlled oscillator VCO circuit does.

It is an electronic device that creates a continuous signal often a square wave and uses a voltage to change how fast that signal vibrates, making the sound higher or lower.

These VCO circuits are used in many things, like radios to adjust the station or even in some musical instruments to create different tones.

Circuit Working:

Parts List:

This circuit is famous for astable multivibrator which produces a square wave and whose frequency is determined by the voltage at V1.

Higher voltages result in higher frequencies where as lower voltages lead to lower frequencies.

Many other oscillators are also responsive to voltage variations.

Voltage Controlled Oscillator VCO circuits serve various purposes.

They can audibly indicate changes in circuit or power source voltage provide warnings for excessive voltage levels and are commonly utilized in electronic musical instruments and devices.

Formulas:

The primary distinction between an astable multivibrator and a VCO is the addition of a control voltage to modify the oscillation frequency, even if the fundamental idea is the same.

Basic Formula for Astable Multivibrator:

The frequency of oscillation (f) for a conventional astable multivibrator with two identical RC sections is provided by:

f = 1 / (1.4 * R * C)

where,

• In hertz, f stands for frequency.
• R is the ohms of resistance.
• C represents capacitance in farads.

VCO Formula in General:

Although the exact formula for a VCO varies depending on the implementation, the overall connection may be stated as follows:

f = K * (V_control – V_offset)

where,

• f is the frequency of oscillation
• K is a proportionality constant that circuit elements determine.
• The control voltage is denoted by Vcontrol.
• A voltage offset called Voffset is used to determine the intended frequency range.

Note:

Dedicated VCO ICs or oscillator circuits with greater performance characteristics are frequently selected for high precision VCO applications.

How to Build:

To build a Simple Voltage Controlled Oscillator Circuit follow the below mentioned steps:

Construction Steps:

• Connect R1 and R2 in series between the supply voltage Vcc.
• Connect C1 between the junction of R2 and R3.
• Connect Q1 and Q2 in a cross coupled configuration, with their emitters connected to ground through D1 and D2 diodes.
• Connect the collectors of Q1 and Q2 to Vcc.
• Connect base of Q1 through capacitor C1.
• Connect base of Q2 through capacitor C2.

Adjustment and Testing:

• Use an oscilloscope to measure the output frequency at the collector of Q1 or Q2.
• Verify that the circuit operates within the desired frequency range and responds to changes in the control voltage.

Notes:

• This is a basic VCO design and can be further refined for specific applications.
• The choice of component values will determine the frequency range and stability of the oscillator.
• Careful attention to component selection and layout is crucial for reliable performance.

Conclusion:

A Voltage Controlled Oscillator VCO circuit is an electronic oscillator that produces an output signal with a frequency that can be controlled by a voltage input.

It is used in various applications where precise frequency control is required, such as in communication systems, test equipment and electronic musical instruments

References:

Voltage-controlled oscillator

The Basics of Voltage Controlled Oscillators (VCOs) and How to Select and Use Them