the amplifier · During the positive half cycle Input signal ( V S ) increases the forward voltage across the emitter-base. As a result, the base current ( I B in μA) increases. Consequently, the collector current ( I C in mA) increases β times. This increases the voltage drop across R c ( I c R c ) which in turn decreases the collector-emitter voltage ( V CE ).
Therefore, the input signal during the positive half cycle produces negative half cycle of the amplified signal at the output. Hence, the output signal is reversed by ° as shown in Figure . (b). · During the negative half cycle Input signal ( V S ) decreases the forward voltage across the emitter-base.
As a result, base current ( I B in μA) decreases and in turn decreases the collector current ( I C in mA). The decrease in collector current ( I C ) decreases the potential drop across R C which in turn increases the collector-emitter voltage ( V CE ). Thus, the input signal during the negative half cycle produces positive half cycle of the amplified signal at the output.Therefore, phase reversal is observed during the negative half cycle of the input signal also as shown in Figure . (b).
. . Transistor as an oscillator An electronic oscillator basically converts DC energy into AC energy of frequency ranging from a few Hz to several MHz. Hence, it is a source of alternating current or voltage.
Unlike an amplifier, oscillator does not require any external signal source. Basically, there are two types of oscillators: Sinusoidal and non-sinusoidal . Sinusoidal oscillators generate oscillations in the form of sine waves at constant amplitude and + V CC V R E R R C R I C V S C C C C E 0V O E C I B I E Input AC signal +ve –ve +ve –ve Output AC signal Figure . (a) Transistor as an amplifier (b) Input and output waveforms showing phase reversal.
To start with, the Q point or the operating