The complementary output circuit signal can pass through the diode: the sine signal has positive and negative two and a half periods in one cycle, indicating that the current has two directions, while the diode only allows one-way conduction, and the positive half period of conduction will be displayed, and the negative half period of non-conduction is equivalent to an open circuit.

Prevent the amplifier circuit from being overloaded due to excessive signal input. Generally, they are connected in parallel to the signal input terminals of small signal amplifiers. If there is only one diode, it absorbs the part of the signal that can turn on the diode to prevent the reverse signal from being input at the signal end.

Principle of PN junction formation:

Because boron atom has only three valence electrons, it forms valence bonds with surrounding silicon atoms. Due to the lack of an electron, a vacancy is generated in the crystal, and when the electrons on the adjacent valence bonds gain energy, it is possible to fill this vacancy.

Boron atoms become immobile negative ions, and the valence bond of silicon atoms originally forms holes due to the lack of an electron, but the whole semiconductor is still neutral. In this p-type semiconductor, holes are the majority carriers and free electrons are the minority carriers.