:If the external emitter resistance is small or zero, then you really can't use a constant base voltage as a bias as it makes things way too sensitive to variations in R E and ?.
32.
The feedback amplifier maintains the emitter voltage equal to the input voltage, so the base voltage is one V BE drop above that and the emitter current I E is always proportional to the input voltage.
33.
The problem is that because of the high gain ( presuming a silicon device ), only a minute rise and fall in base voltage is sufficient to turn the transistor on and off ( respectively ).
34.
One advance let a relatively small base voltage excite a full flow of electrons that had no fluctuations, allowing transistors to act as on-off switches, or, in mathematical terms, " 0 " and " 1 ."
35.
If you hold the base at a constant voltage ( relative to the circuit's overall V CC ), then the emitter "'must "'be about one diode drop ( so, usually, about 0.6v ) below the base voltage.
36.
There is no negative feedback since the emitter voltage does not change at all when the input base voltages change . " he common quiescent current vigorously steers between the two transistors and the output collector voltages vigorously change.
37.
Intuitively, this behavior can be also understood by realizing that the base-emitter voltage in the bipolar transistor is very insensitive to bias changes, so any change in base voltage is transmitted ( to good approximation ) directly to the emitter.
38.
:IMO this is not really a good switch circuit ( unless the base voltage is slightly greater than the positive supply voltage ) because the voltage applied to the load can only be about 0.6 v below the base voltage and the transistor cannot saturate.
39.
:IMO this is not really a good switch circuit ( unless the base voltage is slightly greater than the positive supply voltage ) because the voltage applied to the load can only be about 0.6 v below the base voltage and the transistor cannot saturate.
40.
The Miller effect negatively affects the performance of the common source amplifier in the same way ( and has similar solutions ) . When an AC signal is applied to the transistor amplifier it causes the base voltage VB to fluctuate in value at the AC signal.
