Final answer:
A VCO circuit can be designed in Proteus using an OPAMP, diodes, a potentiometer, a transistor, and capacitors to create a circuit whose frequency output varies with the input voltage.
Step-by-step explanation:
Designing a Voltage-Controlled Oscillator (VCO) in Proteus involves creating a circuit that varies its frequency output based on the input voltage. The components required for this circuit include an operational amplifier (OPAMP), diodes, a potentiometer, a transistor, and capacitors. The OPAMP can be used in a configuration that allows the frequency of oscillation to be adjusted through the potentiometer. Diodes may be used for frequency shaping and stabilization, while capacitors establish the time constant for oscillation. The transistor will act as a switch in the feedback loop to maintain oscillation. By using these components in a systematic layout, the VCO can be constructed and simulated in Proteus for various applications.