Radio Theory Handbook. Beginner to Advanced. by Ronald Bertrand

Author:Ronald Bertrand [Bertrand, Ronald]
Language: eng
Format: epub
Published: 2016-07-07T14:00:00+00:00

POINT CONTACT DIODE

Figure 19-24.

A point-contact germanium or silicon diode is a semiconductor pellet (or germanium of silicon) with fine gold-plated tungsten wire with a diameter of about 80 to 400 microns (millionths of a metre) and a sharp point, makes contact with the polished top of the semiconductor pellet and is pressed down on it slightly from a spring contact. This cat’s whisker, as it is known, is connected on the right-hand side to a brass plate which is the cathode. The semiconductor injects electrons into the metal. The energy level between the valence electrons in the semiconductor pallet and the tip of the wire produces a diode action. The contact area exhibits extremely low capacitance.

Because of the low capacitance, point contact diodes can be used for applications at extremely high frequencies. Ordinary PN-junction diodes have too much junction capacitance for use at these high frequencies.

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