Relationship between the operating frequency of the PN junction of the diode junction area - "self-learning electronic technology Slag Notes"
Book Original : by the structure, point contact type diode, and a planar surface contact type categories. Point-contact diodes (typically germanium tube) is very small junction area of the PN junction (small junction capacitance), a large current can not pass, but the good high-frequency performance, it is generally applicable to high and low power work , also used as switching elements in a digital circuit. Surface contact type diode (typically silicon tube) of a large junction area of the PN junction (junction capacitance large), so that a large current through, but the low frequency operation , commonly used as the rectifier. Planar type diode rectifier and the power switch can be used as a digital circuit.
Question and answer
Q: the PN junction has a capacitance effect, capacitance is calculated according to the formula
\[X_c= {1\over2{\pi}fC}\]
The larger the capacitor capacitance should be smaller, high frequency, the better it?
A: capacitance will produce a high frequency signal PN junction is formed "via", larger junction area larger capacitance. At the same capacitance value, the frequency \ (F \) high to a certain extent will cause the capacitance \ (X_c \) is too small to affect the rectifier or detector function . The small junction capacitance when the high operating frequency will not lead to \ (X_c \) is too small.