Which diode is used for frequency tuning?
The varicap diode or varactor diode provides a way or having a voltage controlled variable capacitance in a circuit. Varactor or varicap diodes are used mainly in radio frequency or RF circuits to provide voltage controlled variable capacitance.
What is tuning in resonance?
When a coil and capacitor are said to. be tuned to resonance, the inductive and. capacitive reactances are equal but opposite. in action.
How do you use a varactor diode?
In forward bias, the diode allows the current to flow through it. During reverse bias, it blocks the flow of current. This reverse biasing is used in the case of the varactor diode. Based on the characteristics of voltage and current and the requirement the diodes are classified as Tunnel diode, Zener diode, and so on.
How is a varactor diode used in a tuning circuit?
Varactor diodes are rated to run up for dozens of V in reverse bias; exceeding this value can cause the varactor diode to run highly nonlinearly, breakdown, or both. For applications requiring tuning of RF circuits, circuits with varactor diodes will use an input AC signal that has some DC offset (Vdc).
What is the capacitance equation for a varactor diode?
The image below shows the schematic symbol and capacitance equation for a varactor diode. Schematic symbol for a varactor diode and capacitance equation. The exponent in the denominator γ is akin to an ideality factor in a standard diode, ɸ is the diode’s built-in voltage, and C0 is the diode’s capacitance at zero applied voltage.
How does reverse bias voltage affect the capacitance?
When the reverse bias voltage is increased, the width of the depletion region also increases, which decreases the capacitance. The image below shows the schematic symbol and capacitance equation for a varactor diode. Schematic symbol for a varactor diode and capacitance equation.
How does a tuning circuit in a TV work?
Nowadays, everything in a TV is digital, but the tuning circuit in an old TV has many applications outside of finding cartoons to watch on Saturday morning. The important circuit element that makes this work is a varactor diode.