A Voltage-Controlled Oscillator (VCO) is an electronic circuit that generates a periodic waveform, typically a sine or square wave, whose frequency can be adjusted by changing the input voltage. VCOs are widely used in various applications, including phase-locked loops and frequency modulation, where precise frequency control is essential. The output frequency of a VCO is directly proportional to the input voltage, allowing for smooth and continuous frequency tuning. This characteristic makes VCOs valuable in communication systems, signal processing, and synthesizers, where they help create stable and adjustable signals for transmitting and processing information.