whereas the voltage gain for the range of frequencies between 50Hz and 20 KHz is constant. The frequency response of a RC coupled amplifier is as shown in the following graph.įrom the above graph, it is understood that the frequency rolls off or decreases for the frequencies below 50Hz and for the frequencies above 20 KHz. Frequency Response of RC Coupled Amplifierįrequency response curve is a graph that indicates the relationship between voltage gain and function of frequency. Because the phase reversal is done two times by the two stage CE configured amplifier circuit. Hence, in a multistage amplifier, only the gain of the last stage remains unchanged.Īs we consider a two stage amplifier here, the output phase is same as input. This is because when a second stage is made to follow the first stage, the effective load resistance of the first stage is reduced due to the shunting effect of the input resistance of the second stage. The important point that has to be noted here is that the total gain is less than the product of the gains of individual stages. Thus the signal is amplified in stage by stage action. This becomes the input of the next stage, whose amplified output again appears across its collector load. When an AC input signal is applied to the base of first transistor, it gets amplified and appears at the collector load R L which is then passed through the coupling capacitor C C to the next stage. The figure below shows the circuit diagram of RC coupled amplifier. The capacitor C C is the coupling capacitor that connects two stages and prevents DC interference between the stages and controls the shift of operating point. The input capacitor C in present at the initial stage of the amplifier couples AC signal to the base of the transistor. The resistor R L is used as a load impedance. The emitter by-pass capacitor C e offers a low reactance path to the signal. The potential divider network R 1 and R 2 and the resistor R e form the biasing and stabilization network. The two stage amplifier circuit has two transistors, connected in CE configuration and a common power supply V CC is used. The constructional details of a two-stage RC coupled transistor amplifier circuit are as follows. Construction of a Two-stage RC Coupled Amplifier This is the mostly used coupling technique in amplifiers. The resistance-capacitance coupling is, in short termed as RC coupling.
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