Hello everybody! How are you? I'm a fresher here and i'll begin with a silly question: what in this symbol in the red circuit. Any help ? thank you>

 

A bi-directional gate.
Max.

 

A bi-directional gate.
Max.

CMOS chips like the 4016/4066 spring readily to mind - there's wider signal applications types with "DG" prefix - but I don't remember the manufacturer.

The OP's schematic looks sort of similar - ish to a crosspoint switch used in telephone systems.

 

To be more specific, it's a transmission gate...

 

CMOS chips like the 4016/4066 spring readily to mind - there's wider signal applications types with "DG" prefix - but I don't remember the manufacturer.

The OP's schematic looks sort of similar - ish to a crosspoint switch used in telephone systems.

You might be thinking of DG406, DG407, DG408 etc. made by many companies, Intersil, Maxim, Analog Devices.