Q. Explain the significance of the Coupling capacitor and the RE - CE circuit.
The function of the coupling capacitor is to isolate the amplifier input circuit from the source. Since capacitor blocks dc it does not allow the dc components from the input circuit to get to the base of transistor and to change the Q point.
Additional requirement of Cin is that it must pass the input ac signal unattenuated. Hence the lower cut-off frequency (LCF) of the amplifier is determined by the coupling capacitor.
The RE - CE combination is connected in series with the cathode to obtain temperature stability stability and proper functioning of the amplifier.