The circuit diagram shows the two stage RC Coupled transistor amplifier using voltage divider bias in CE configuration. The connection to second stage from the first stage is done through the coupling capacitor Cc.C1 couples input signal to first stage and C2 couples the signal from first stage to the second stage.
R1,R2 provide the required biasing and RE provides the stabilization. CE bypasses ac across the resistor Rc.
When the ac input signal is applied to the input of the first stage, it gets amplified and appears at its output with a phase difference of 180° This amplified signal is fed to the input of the second stage through the coupling capacitor C2. The second stage further amplifies the signal and produces a phase reversal of 180° with respect to its input signal. The signal is inverted twice and the input and output of two stage CE amplifier are in phase.
Frequency response:
At low frequencies, the coupling capacitor Cc offers high reactance Xc. Hence it allows only a small part of the signal to pass from one stage to the next stage. Thus gain is less at low frequencies.
At high frequencies, the coupling capacitor Cc offers a low reactance and acts like a switch. Hence , due to loading effect of the next stage increases and the gain decreases.
In mid-frequency range, the effect of coupling capacitor is such that it maintains a constant voltage gain. When the frequency increases, the capacitive reactance Cc decreases which tries to increases the gain. As the capacitive reactance decreases, the loading effect of next stage reduces the gain. The voltage gain remains a constant as the two factors cancel each other.
