Q.Draw the circuit diagram and explain with graph the frequency response of CE amplifier.

The frequency response is the graph of a CE amplifier's voltage gain against frequency, which stays constant only over a middle band and falls at both low and high frequencies because of circuit capacitances. …

[!TLDR]

A CE amplifier's voltage gain is flat only in a mid-frequency band, falling at low frequencies (coupling/bypass capacitor reactance) and at high frequencies (junction/stray capacitance); the bandwidth is $f_H-f_L$ at the 0.707$A_m$ (3 dB) points.

Circuit: a single-stage voltage-divider-biased CE amplifier — $R_1,R_2$ set the base bias, $R_C$ is the collector load, $R_E$ with bypass capacitor $C_E$ stabilises the bias; the input signal is coupled through $C_1$ and the output through $C_2$.

Frequency-response graph: voltage gain $A_v$ is plotted against frequency $f$ (log scale). The curve rises at low frequencies, becomes flat at a maximum value $A_m$ over the mid band, and rolls off at high frequencies. Three regions:

1. Low-frequency region: the coupling capacitors $C_1,C_2$ and the emitter bypass capacitor $C_E$ have high reactance $(X_C=1/2\pi f C)$. $C_1$ and $C_2$ then drop part of the signal and pass only a fraction to the next stage/load, while an unbypassed $R_E$ introduces negative feedback; both reduce the gain. So the gain is small at low frequencies.

2. Mid-frequency region: here the reactances of $C_1,C_2,C_E$ are so small that these capacitors act as shorts, while the transistor junction and stray capacitances are still large enough in reactance to be treated as open. The gain is therefore constant at its maximum value $A_m$. …