MOSFET is the field effect tube:  
1. The field effect tube can be applied to zoom. Due to the high input impedance of the venue effect, the coupling capacitance can be smaller without having to use electrolytic capacitors.  
2. The input impedance with high field effect tube is very suitable for impedance transformation. Commonly used in the input level of multi -level amplifiers.  
3. The field effect tube can be used as a variable resistor.  
4. Field effect tube can be easily used as constant stream.  
5. The field effect tube can be used as an electronic switch.