what are the 5 important parameters of BJT amplifier?

Answer 1

I would say these are the 5 important parameters:

1. Gain
2. Frequency response
3. Input impedance
4. Output impedance
5. Bias point (Class A, AB, B, C)

Actually those are the 5 main parameters of any type of amplifier, BJT or otherwise.

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Answer 2

I would say the following (not necessarily in order of importance):

- bias voltage
basically an offset voltage that's used to ensure that the transistor is operating in its linear region.

- cutoff voltage
the voltage below which the transistor does not operate

- active region
the linear region. A linear increase in the input will produce a linear increase in the output.

- current gain
or beta. Your ratio of output current to input current.

- saturation point
the point at which the BJT is no longer in the operating region. It occurs when you pass the high end of the operating region, and your output capacity tails off here. A linear increase in the input will not produce a corresponding linear increase in the output.