Among these which one is correct about the characteristics of the transistor?
Right Answer is:
It has the high input impedance
The input and output impedance of transistors depends on quite a lot on the technology of the transistor and on the way it is used in a circuit.
A bipolar transistor used as a common collector amplifier will have a high input impedance and a low output impedance.
The same transistor used as a common base amplifier will have a low input impedance and a high output impedance.
We typically don’t like low input impedance because we would like to control things using very little current. A low input impedance draws current. Also, we typically like low output impedance when the transistor is on and a high output resistance when it is off.
Advantages of bipolar junction transistor (BJT) are as given below,
- The bipolar junction transistor (BJT) has a large gain bandwidth.
- The BJT shows better performance at high frequency.
- The large value of current gain, β
- The large value of transfer conductance gm
- The BJT has a better voltage gain.
- The BJT can be operated in low or high-power applications.
- The BJT has a high current density.
- There is a low forward voltage drop.
- BJTs have a very predictable turn-on voltage, i.e. typically 0.7V Vbe
- A BJT needs a small amount of current to switch on the transistor.
- BJT amplifier stages are much more linear than MOSFET amplifier stages, as the gain doesn’t depend on the bias voltage. This gives better fidelity.
- BJT’s are capable of handling higher output currents for signal outputs and can have a lower output impedance. In amplifiers intended to drive a low input impedance load or deliver significant amounts of power, this is a huge advantage. Many of the highest quality op-amps are made with a BiCMOS process using a BJT pair for the output buffer stage.
There are some disadvantages of bipolar junction transistor (BJT) are as given below,
- The bipolar junction transistor (BJT) more noise produced.
- Special isolation regions are required between individual devices in an
- More number of diffusion steps are required for its manufacturing
- Larger turn-off time
- Operation of the BJT relies on the transport of minority carriers and that is significantly affected by incident electromagnetic radiation. (Hence, the existence of photo-diodes and photo-transistors, etc.)
- BJT has low thermal stability.
- BJT’s are current-operated devices rather than voltage-operated. Most of the time this means higher power consumption.
- BJT has a positive temperature coefficient at a high current level. It means in BJT collector current increases with the increase in temperature. This characteristic leads the BJT to thermal breakdown.
- The switching frequency of BJT is low.
- It has a very complex base control. So it may lead to confusion and requires skillful handling.