When the junction
diode is reverse biased, the insulating barrier widens.
The higher the
reverse voltage the wider the barrier becomes.
The barrier forms
the dielectric, of variable width, of a capacitor.
The N and P
type cathode and anode are the two plates of the capacitor.
In the diagram,
the diode and coil form a resonant circuit.
The capacitance
of the diode, and thereby the resonant frequency, is varied by means of
the potentiometer controlling the reverse voltage across the varicap.
The capacitor
prevents the coil shorting out the voltage across the potentiometer. |
