Question

FET is a good signal chopper because
1. It exhibits no offset voltage at zero drain current
2. It occupies less space in integrated form 
3. It is less noisy
4. It has got high input impedance

Answer 1

Correct Answer - Option 1 : It exhibits no offset voltage at zero drain current

Offset Voltage:

• Offset voltage (V_os) is defined as the voltage that must be applied to the input to cause the output to be 0.
• Because of offset voltage, the output is not zero even when the input is zero. It is therefore considered as one of the problems when dealing with transistors.
• Offset voltage is the result of a mismatch in the base-emitter voltages of the differential input transistors (the gate-source voltage mismatch in FET-input amplifiers) and is different from a DC input signal.

 

Advantages of FET:

• FET gas high input impedance of several megaohms. This provides good isolation between the input and the output. 
• High input resistance (of the order of 100 MΩ or more)
• FET typically produces less noise than a BJT.
• Relatively immune to radiation.
• Exhibits no offset voltage at zero drain current .
• Better thermal stability.
• FETs are easier to manufacture than the BJT