Variable-capacitance diodes, also known as varactor diodes or varicap diodes, are semiconductor devices with a varying capacitance depending on the applied voltage. They are designed to function as voltage-controlled capacitors, where the capacitance changes inversely with the applied voltage. Variable-capacitance diodes find extensive use in tuning circuits, frequency modulators, voltage-controlled oscillators (VCOs), and phase-locked loops (PLLs) in communication systems and electronic circuits requiring frequency tuning or voltage-controlled parameters. Diodes with wider capacitance ranges, higher voltage ratings, and superior tuning performance may command higher price points. When purchasing these diodes, consider the specific tuning requirements of your circuit. Determine the capacitance range, voltage tuning range, and tuning linearity needed for your application. Pay attention to the diode's voltage sensitivity (capacitance-voltage characteristics), reverse breakdown voltage, and temperature stability. Choose the appropriate package type and mounting style for your circuit board.