The following are the applications of RC coupled amplifier. The voltage and power gain are low because of the effective load resistance.ĭue to poor impedance matching, power transfer will be low. The following are the disadvantages of RC coupled amplifier. It becomes more compact with the upgrading technology. The circuit is simple and has lower cost because it employs resistors and capacitors which are cheap. The frequency response of RC amplifier provides constant gain over a wide frequency range, hence most suitable for audio applications. The following are the advantages of RC coupled amplifier. But this lower capacitance reactive increases the loading effect of the next stage by which there is a reduction in gain.ĭue to these two factors, the gain is maintained constant. If the frequency increases, the reactance of the capacitor C C decreases which tends to increase the gain. The voltage gain of the capacitors is maintained constant in this range of frequencies, as shown in figure. Hence the voltage gain rolls off at high frequencies. Along with this, as the capacitance of emitter diode decreases, it increases the base current of the transistor due to which the current gain (β) reduces. As a result of this, the loading effect of the next stage increases, which reduces the voltage gain. So, a capacitor behaves as a short circuit, at high frequencies. above 20 KHz)Īgain considering the same point, we know that the capacitive reactance is low at high frequencies. With all these factors, the voltage gain rolls off at low frequencies. Hence it cannot shunt the emitter resistance effectively. The reactance of the emitter by pass capacitor C E is also very high during low frequencies. The reactance of input capacitor C in and the coupling capacitor C C are so high that only small part of the input signal is allowed. At low frequencies, the reactance is quite high. The capacitive reactance is inversely proportional to the frequency. It means that the capacitive reactance is inversely proportional to the frequency. 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. Emitter Follower & Darlington Amplifier. Transformer Coupled Class A Power Amplifier.
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