CE (Common- Emitter) Amplifier amplifies the given small input voltage to large output voltage. The frequency response of an amplifier is the graph of its gain versus the frequency. In the middle range of frequencies, the voltage gain is maximum. The amplifier is normally operated in this range of frequencies. At low frequencies, the voltage gain decreases because the coupling and bypass capacitors no longer act like short circuits; instead some of the ac signal voltage is attenuated. The result is a decrease of voltage gain as we approach zero hertz. At high frequencies, voltage gain decreases because the internal capacitances across the transistor junctions provide bypass paths for ac signal. So as frequency increases, the capacitive reactance becomes low enough to prevent normal transistor action. The result is a loss of voltage gain.
