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Explain base biased C.E. amplifier using waveform
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A single stage RC coupled amplifier using transistor as an active device is:-

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$C_1,C_2→$ Coupling capacitors.

$R_L→$ Load resistors is coupled to the amp thru the coupling capacitor, this amp is called as $R_C$ coupled amplifier.

The BJT is connected in common emitter CE configuration, therefore the amp is called CE amp. I/p coupling capacitor $C_1 :$

I/p coupling cap $C_1$ is used for coupling the ac voltage $V_1$ to the base of BJT.

As the capacitor blocks dc, the cap helps to block any dc component present in $V_i$ and couples only ac component of the i/p sig. This cap also ensures that the dc biasing conditions of the transistor remain unchanged even after application of i/p signal.

For the coupling capacitor $C_1$ to work properly its value should be large enough so that its reactance is less than 10 % of the i/p resistance of the amp at the lowest operating frequency of the amp.

O/p coupling capC_2 :

The capacitor couples the amplifier o/p to load resistance or to the next stage of the amplifier.

It is used for blocking the dc and passing only the ac part of the amplified signal to the load.

Operation of the amplifier:

When ac i/p → absent, value of dc of base current of the transistor is $I_{BQ}$ which is called quiescent base current.

Corresponding to $I_{BQ}$ , a quiescent dc collector $I_{CQ}$, also flows through the BJT and collector emitter voltage is $V_{CEQ}$. All this happens because we have biased the transistor in its active region using the biasing components.

when small ac sinussoidal is applied at the i/p of the amp, an alternating base current starts flowing in the circuit.

This base current varies above and below the Q pt. value of the base current $(I_{BQ})$. Thus we can say that the ac signal is superimposed on the DC current $I_{BQ}$.

Due to these variations in the base current, proportional variation take place in the collector current, because $I_C=BI_B$. As $I_B↑ ,I_C$ also $↑$ $→I_B$ and $I_C$ In phase but $I_C$ is a magnified version of $I_B.I_C$ varies above and below its Q pt. value $I_{CQ}$. This varying $I_C$ passes through the collector resistor $R_C$ to produce a varying voltage drop $I_C R_C$ across it. This voltage drop $I_C R_C$ is in phase with the collector and base currents as shown. Collector voltage $= V_C=V_{CC}-I_C R_C$ ∴ With change in voltage drop $I_C R_C$ , the collector voltage also will vary. However, $V_C$ and $I_C R_C$ will vary in exactly opposite manner w.r.t to each other.

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