What is the normal operating range of a varactor diode and its working principle

Variable capacitance diode, also known as variable capacitance diode or capacitive diode, is a diode that can change its capacitance value by changing voltage or current. It usually consists of two electrodes and a variable medium. The working principle of varactor diodes involves the characteristics of their structure and materials.

The structure of a varactor diode typically consists of two electrodes and a variable dielectric. One of the electrodes is a metal plate called a fixed plate, and the other electrode is a movable metal plate called a movable plate. The space between two electrodes is filled with a variable dielectric, typically a high dielectric constant material such as aluminum oxide or aluminum nitride.

When the varactor diode is in its normal working area, the distance between the movable plate and the fixed plate is fixed, and the capacitance value remains unchanged. When the applied voltage or current changes, the movable plate will be affected by the electric field force, thereby changing its position and distance from the fixed plate. This will cause a change in the capacitance value.

The working principle of a varactor diode can be explained through the following steps:

1. Unbiased state: In the absence of external voltage or current, the varactor diode is in an unbiased state. At this point, the movable board is located in the middle of the fixed board, and the capacitance value is in the middle.

2. Bias state: When an external voltage or current is applied to a varactor diode, an electric field is formed in the capacitor. This electric field will apply a force to the movable plate, causing it to move to a new position. The movement of the activity board will change the effective capacitance value of the capacitor.

3. Change in capacitance value: When the movable plate moves to a new position, the distance between the movable plate and the fixed plate changes. Due to the inverse proportionality between the capacitance value and the distance between the electrodes, the capacitance value will change accordingly. When the movable board approaches the fixed board, the capacitance value increases; When the movable board moves away from the fixed board, the capacitance value decreases.

4. Scope: The range of capacitance variation of a varactor diode depends on the electric field strength and the distance between the movable plate and the fixed plate. Usually, the capacitance value of a varactor diode can vary from a few picofarads (pF) to several hundred pF.

The working principle of varactor diode is based on the effect of electric field force on the movable plate. By changing the voltage or current, the magnitude and direction of the electric field force can be altered, thereby controlling the position of the movable plate and the distance between it and the fixed plate. This enables varactor diodes to be used as variable capacitors in capacitor circuits to meet different circuit requirements.