Common-emitter amplifier questions

[Resistanceisfutile]

Hi, I read an article on Circuitstoday about the "common-emitter amplifier".
I had a bunch of questions to ask, just to check I understood if it:


1. Does no biasing mean lower (than nessecary) voltage? And does heavy biasing mean higher (than nessecary) voltage?
2. If a transistor operates in the cutoff region/fully off (as an amplifier), will the output lose parts of the wave form because it has been used to power the transistor?
3. If a transistor operates in the saturation region/fully on (again, as an amplifier) will the transistor not respond to the changes in the input current at the base because it is saturated?
4. Although the article mentions this circuit is for preamplification, if I modified the circuit so that it had bandwidth capable of responding to RF, could I use this as a radio pre-amplifier?

 

[Audioguru]

1) Biasing of a transistor is its amount of base current. No biasing is no base current so the transistor conducts no current without an input signal and rectifies an AC input signal.
Heavy biasing is when it has a high base current which is when a transistor is used as a switch so that it completely turns on as much as it can.

2) When a transistor is "cutoff" then it has no base current and does not conduct any current. Then those parts of a waveform at its output are not produced (clipped) and are lost. The transistor is not powered when it is cutoff.

3) A saturated transistor is turned on as hard as it can. Then those parts of a waveform that require it to turn on more are not produced (clipped) at its output.

4) An audio preamp circuit has a very low input signal level and does not have high input levels. It has high voltage gain and its high frequency response is limited.
A radio preamp circuit is designed for the frequency it operates at and is usually tuned to it. It has weak input signals and might also have very strong local signals so it must have AGC to reduce its gain when receiving strong local signals to prevent overload.

 

[LvW]

1) Biasing of a transistor is its amount of base current. No biasing is no base current

Before a base current can exist a proper base-to-emitter voltage is required - as a first biasing condition.

 

[Audioguru]

Before a base current can exist a proper base-to-emitter voltage is required - as a first biasing condition.

Of course. It is assumed that there is enough voltage to create the base current.

I do not want to argue whether a current causes a voltage or whether a voltage causes a current.

 

[LvW]

I do not want to argue whether a current causes a voltage or whether a voltage causes a current.

Right - because there is nothing to argue.