Amplifier and amplification | RC couple amplifier | Coupling


Amplifier and amplification

The process of rising of strength of input signal without changing its shape and frequency is called amplification and the device which do this work is called amplifier, the bipolar junction transistor (p-n-p  &n-p-n) in common emitter configuration with voltage divider biasing method is used as amplifier in electronic devices
Amplifier and amplification | RC couple amplifier | Coupling
Amplifier and amplification | RC couple amplifier | Coupling
 

Single stage RC couple amplifier

The common emitter configuration of n-p-n transistor is widely used in electronic devices for faithful amplification the simple circuit diagram for n-p-n transistor in common emitter configuration with voltage divider biasing is shown in figure as follow the single stage RC couple amplifier circuit may be explained input wise as follow

Biasing circuit

In n-p-n transistor use as in common emitter configuration in bias using voltage divider biasing method which consist the series combination of two resistor R1 and R2 as shown in figure the voltage across R2 is used as input voltage which makes base and emitter junction in forward bias condition

Capacitor

The single stage RC couple amplifier circuit consist three capacitor CIn  CE, Cc which are discuss as follow

Input capacitor CIn

Before amplification of AC input signal at base and emitter a capacitor CIn is used to avoid theloading effect of DC component (if any) of applied AC input signal if input capacitor is not use then the DC component of input signal if present will change the biasing condition of input terminal i.e. base emitter terminal hence no faithful amplification is achieve

Emitter capacitor (CE)

In presence of AC input signal and base emitter signal and the biasing batteries AC as well as DC current starts flowing through the transistor Ex-at the emitter of n-p-n transistor the emitter current is flowing out iE
                                                                                iE=ie+IE
here iE=is AC+DC emitter current
         ie=is the pure AC emitter current
         IE=is the pure DC emitter current
Since amplification is achieve in AC input signal only hence we need to separate AC output current from the DC current the capacitor offer zero resistivity for AC current and infinite resistance for DC current therefore at emitter terminal the AC emitter current will flow through capacitor and DC emitter current will flow across emitter resistance RE

Coupling capacitor

To obtain the AC component of collector current after faithful amplification and another capacitor Cc is used called coupling capacitor therefore the amplified AC output signal taken between Cc and CE the coupling capacitor is also used to couple the output of one stage of RC coupled amplifier to the input of next stage of RC coupled amplifier

Transistor biasing

In RC couple amplifier an n-p-n transistor is used in common emitter configuration due to its high current gain the n-p-n transistor is used in state of n-p-n transistor because in n-p-n transistor the majority carrier are electron hence there mobility will be higher than holes of n-p-n transistor
Input signal
In RC couple amplifier the amplification of AC signal takes place therefore the AC signal which have to be amplified is applied across R2 of bias transistor with the help of a capacitor CIn

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