1. Advantages and disadvantages of FETs
The advantages of FETs relative to BJTs are summarized as follows:
- FETs are voltage-sensitive devices with high input impedance (on the order of 107 to 1012 Ω). Since this input impedance is considerably higher than that of BJTs, FETs are preferred over BJTs for use as the input stage to a multistage amplifier.
- One class of FETs (JFETs) generates lower noise than BJTs.
- FETs are more temperature stable than BJTs.
- FETs are generally easier to fabricate than BJTs. Greater numbers of devices can be fabricated on a single chip (i.e., increased packing density is possible).
- FETs react like voltage-controlled variable resistors for small values of drain-to-source voltage.
- The high input impedance of FETs permit them to store charge long enough to allow them to be used as storage elements.
- Power FETs can dissipate high power and can switch large currents.
- FETs are not as sensitive to radiation as BJTs (an important consideration for space electronic applications).
There are several disadvantages that limit the use of FETs in some applications. These are:
- FETs amplifiers usually exhibit poor frequency response because of high input capacitance.
- Some types of FETs exhibit poor linearity.
- FETs can be damaged in handling due to static electricity.